Ice Climatology of the Beaufort Sea W.E. MARKHAM Technical Report No. 26

I C E CL IMATOLOGY I N THE BEAUFORT S EA

�� . E . �1arkham

I ce C l imatol ogy Dept . of the Envi ronment

Treb 1 a Bu i l d i ng Ottawa , Ontar i o

K1 A OH3

Beaufort Sea Tech n i ca l Report #26

Bea ufort Sea Proj ect Dept . of the Env i ronment

51 2 Federa l Bu i l d i ng 1 230 Government St .

Vi ctori a , B.C. V8W l Y4

December 1 97 5

TABLE OF CONTENTS Page

1 . S UMMARY 1 2 . I NTRODUCTION 1 3 . STUDY AREA 2 4 . SOURCES OF DATA 2

4 . 1 Ice Cl imatol ogy 2 4 . 2 Fl oe Mot i ons 2 4 . 3 Pred i ct ion of the Retreat of the Summer Pack I ce 3 4 . 4 Ice Fl oe S i zes i n the Southern Beaufort Sea 3

5 . R ESULTS 3 5 . 1 Cl imatol ogi cal Study of Ice Cond i t i ons 3

5 . 1 . 1 Med i a n Ice Cond i t ions 3 5 . 1 . 2 Frequency of Occurrence of Vari ou s I ce

Concentrat i ons 5 5 . 1 . 3 Best Ice Year i n F i ve 5 5 . 1 . 4 Worst Ice Year i n F i ve 5 5 . 1 . 5 Number and Timi ng of I n terrupt i ons 5 5 . 1 . 6 I ce Zones 8 5 . 1 . 7 Autumn Ice Bu i l d-up 20

5 . 2 A Study of t he Mot i on of I nd i v i dual I ce Fl oes i n t he Beaufort Sea 2 1 5 . 2 . 1 I ntroducti on 5 . 2 . 2 Satel l i te Imagery

5 . 2 . 2 . 1 Ava i l abl e Data 5 . 2 . 2 . 2 Ana lys i s

5 . 2 . 3 Dri ft Buoys and Beacons

5 . 2 . 3 . 1 Data Ava i l abl e 5 . 2 . 3 . 2 Ana lys i s

5 . 3 Pred i ct i on of the Gross Features of the Summer Retreat

2 1 2 1

2 1 2 2

2 9

2 9 29

of the Pol ar Pack i n the Beaufort Sea 35 5 . 3 . 1 I ntroducti on 3 5 5 . 3 . 2 Method 3 5 5 . 3 . 3 Res ul ts 44

5 . 4 A Study of Fl oe S i ze i n the Beaufort Sea 46 5 . 4 . 1 I ntroduct i on 5 . 4 . 2 Ava i l abl e Data 5 . 4 . 3 Ana l ys i s

6 . D I SCUSS ION 6 . 1 I ce Cl imato l ogy 6 . 2 I nd i v i dual I c e Fl oes 6 . 3 Gross Features of the Summer Retreat of the Pac k 6 . 4 Fl oe Si zes

7 . I MP L I CATI ONS AND RECOMMEN DATI ONS

46 46 49

50

50 57 58 58

59

TABLE OF CONTENTS ( Cont ' d } P age

8 . NEEDS FOR FURTHER STUDY 59 9. REFERENCES 60

APPEND I X I 6 1

APPEND I X I I 6 5

1

1 . SUMMARY

Th i s report cons i sts of four separate stud i es concerned ma i n ly wi th i ce c l imatol ogy i n the southern Beaufort Sea. The fi rst , ba sed on a study of twenty years · of h i s torica l i ce c harts , descri bes the vari ati on of i ce concentrati on wi th the t ime of year for s i x reg i ons wi th d i fferent i c e reg imes . The second descr i bes the mot ion o f i nd i v i dua l i ce fl oes rel a­ti ve to the wi nd . The t h i rd descri bes a reasonabl y accurate method for pred i cti ng t he gross features of the northward retreat of the pol ar pack i ce i n the Beaufort Sea a nd the fourth i s an exami nat i on of the s i ze of i ce fl oes wi th i n vari ou s i ce concentrat i on ranges near the edge of the pol ar pac k.

2. I NTRODUCTION

The Atmospher i c Env i ronment Serv i ce of the . Department of the Env i ronment has fl own i ce reconna i s sance s urveys i n s upport of s h i pp i ng i n the Beaufort Sea s i nce 1 958 . vJeekl y s ummary i ce charts were produced from these surveys . Other i ce reconna i s sance data (wh i ch was col l ected pr ior to and duri ng the construct i on of the DEW L i ne ) i s a va i l ab l e from U . S . Navy observers . I n order to make th i s data more useful i n p l anni ng off­s hore acti v i ti es , an a na l ys i s has reduced these observati ons i nto graphs of the frequency of occurrence of vari ous i ce concentrati ons vs t ime of year for s i x representati ve offs hore reg i ons i n the southern Beaufort Sea . The res u l ti ng graphs shoul d be u sefu l for determ i n i ng expected d urat ion of the operat i ng season for dri l l s h i p s at spec i fi c offs hore s i tes . Res u l ts are descri bed i n Sect ion 5.1 .

Offs hore i ndustr i a l act i v i ty woul d u sua l l y have to be pro tected by an i ce reconna i s sance and weather forecasting serv i ce w i th a n ab i l i ty to pred i ct the movement of i ce fl oes . I t i s therefore i mportant to know the actual moti ons of i nd i v i dua l fl oes and how these mot ions rel a te to wi nds . The ana l ys i s des cri bed i n Sect ion 5.2 i s based on the movement of fl oes wh i ch were tracked i n satel l i te imagery and on observati ons made by Garrett and MacNe i l l (1 976 ) , of the dr i ft of i ce fl oes tagged wi th radi o beacons .

I t wou l d be u seful to have a means of pred i cti ng whether the i ce cond i ­t i o ns wou l d be good , fa i r o r bad i n the ensu i ng s ummer . Al tho ugh weather pred i cti on on a sea sona l bas i s i s not yet po s s i b l e , some useful res u l ts were obta i ned ba sed on the conservati ve nature of the i ce i n the Arct i c Bas i n . The pred i ct i on method i s descri bed i n Sec t i on 5.3.

Exi st i ng c l ima to l og i ca l records for t h e southern Beaufort Sea do not con­ta i n much i nformati on concern i ng fl oe s i zes wh i c h wou l d be useful i n d es i g n i ng offs hore vesse l s or s tructures . The mas s a nd s trength of i ce fl oes i n the area are i mportant for the safety of mar i ne systems . A 50% cover of 1 0 cm thi c k i ce i s of sma l l i mportance to i ce-strengthened off­s hore structures regard l es s of the l ateral d i men s i ons of the fl oes . On the other hand , a s i ng l e fl oe 1 50 cm thi c k and 1 00 m i n d i ameter wou l d wei g h 1 2 , 000 tonnes and cou l d present a probl em i f i t approached a p l at­form . I n the s ummer , fl oes are genera l l y th i c k and hence thei r s i ze i s importa n t . A s peci a l pho togra p h i c mi s s i on wa s fl own i n August 1 974 to obta i n more data and the ana l ys i s of the res u l ts are descri bed i n sect i on 5.4.

2

3 . STUDY AREA

The i ce c l ima te study area i s s hown i n F i gure 1 and i nc l udes not onl y the area off the Macken z i e Del ta but a l s o c overs t he conti nental s hel f wes t of Banks I s l and. Th i s area i s rough l y i ns h ore of t he 400 m i s obath bounded by the coord i nates 70° 30l N 1 41 0W , 7 1 ° 30lN 1 31 0W and 74° 1 51N 1 28°W and extend ea stward to 1 25 °W.

The s tudy on the pred i ct i on of the s ummer i ce retreat of neces s i ty i nc l uded the Arcti c Ba s i n , wh i l e the fl oe s i ze and mot i on stud i es were confi ned wi th i n the i ce c l ima te study area.

4 . SOURCES OF DATA

4.1 I ce C l imatol ogy

The i ce c l i mate of the s ou thern Beaufort Sea has not been documented i n deta i l . An Ice Atl a s of Arcti c Canada (1 960 ) u sed onl y 20 obser­vati on p oi nts i n th i s area and a l though the peri od c overed i n the ana l ys i s was from 1 900 unti l 1 958 there were onl y 2 to 5 years of offshore reports i n any one ana l ys i s per i od but up to 25 at one or two c oa sta l s i tes . S i nce 1 958 Canadi an i ce reconna i s sance fl i g hts over the s outheastern Beaufort Sea have been fl own i n s upport of s h i pp i ng. Us i ng observati ons from t hese fl i g hts a n d meteorol og i ca l data s uc h a s wi nds a nd temperatures , week ly charts i nd i cat i ng the l ocati on , concentrat i on a nd age c l a s si fi cati on of sea i ce have been produced for the i nterval from mi d-May u nt i l l ate October of each year . I n l ater years observat i ons from a i rcraft have been augmented by the use of satel l i te i magery i n the product i on of these c harts. S i nce the i ce observati ons from a i rcraft and sate l l i tes d i d n ot neces sari l y occur on the f i xed dates for wh i c h the week l y charts were prepared , adj u s tments based on wi nd , temperatures and currents were sometimes made. These week ly h i s tori ca l c harts c onst i tute the source of data for the i ce c l ima te s tudy.

4.2 Fl oe Mot i ons

Dur i ng the s ummer of 1 974 , a d i ffi c u l t year for navi gati on i n the s outhern Beaufort Sea , the Arct i c pack rema i ned c l ose i ns hore throu g h­out the sea son. Surface current measurements p l anned by Garrett a nd MacNei l l (1 976 ) u s i ng fl oa t i ng rad i o beacon dr i fters trac ked by a i r­craft , were mod i fi ed by u s i ng the beacons to track i ce fl oe moti ons i nstead. The deta i l ed mot i on s obta i ned i n 1 974 were anal yzed i n rel ati on to the wi nd vel oc i t i es obta i ned from the mean da i l y atmos ­pher i c pres s ure c harts . S im i l ar ly , an exam i nati on was made of fl oe moti ons dep i cted i n satel l i te imagery . ERTS (Earth Res ources Tech ­nol og i ca l Satel l i te or renamed LANDSAT ) i s i n a sun-synchron ous orbi t c i rc l i ng the earth once eac h 1 03 mi nutes . Each orb i t c overs a 300 km w i de path parti a l ly overl app i ng the path fol l owed on t he previ ou s day. The resu l t i s that t he earth i s scanned once each e i g h teen days but at h i g h l at i tudes t hese paths c onverge permi tti ng up to four c onsecuti ve days c overage at l ati tude 800N eac h 1 8 days. Si nce the sen s ors have a 1 00 m resol ut i on , i ce f l oe mot i ons can be tracked q u i te c l osel y as l ong as the d i s tance from s hore where a geograph i ca l fi x i s prov i ded i s n ot too great.

3

4 . 3 Pred i c t i on of the Retreat of the Summer Pac k I ce

For th i s s tudy the two sets of data used were mean month ly atmos ­pher i c press ure charts , ava i l a bl e bac k to the early 1 9501s , and h i stori ca l i ce c harts . These sets were eva l uated to determi ne the extent to wh i c h wi nter or spri ng meteorol ogi ca l cond i ti ons i n the Arc t i c Ba s i n i nfl uenced the i ce regime of the so uthern Beaufort Sea i n the fol l owi n g s ummer .

4 . 4 I ce F l oe S i zes i n the Southern Beaufort Sea

Two sources of data were avai l ab l e . The week ly h i s tor i ca l i ce c harts referred to earl i er formed one source . These not on l y por­trayed t he concentrat i on , type and l ocat ion of sea i ce but to some extent i nc l uded est imates of the d i ameters of i ce fl oes encountered. The second data source was 5 , 200 photographs of t he s urface of the southern Beaufort Sea from a photo-reconna i s sance fl i ght for th i s purpose d uri ng August , 1 974.

5. R ESULTS

5.1 C l ima tol ogi ca l Study of Ice Cond i t i ons

The mai n work of ana l yz i n g h i s tori ca l i ce c harts was conducted by Foundati on of Canada Engi neeri ng Corporati on L im i ted ( FENCO ) under contract to the Department of Envi ronment. Thei r two-vol ume report conta i ns a week-by-week ana lys i s of the i ce cond i ti on s at a ser i es of 1 70 data po i nts on a 1 5 X 20 naut i c a l mi l e gri d wi th i n the s tudy area ( F i gure 1 ) . Computer-drawn week ly maps of med i an i ce cond i tions , best i ce year i n fi ve , worst i ce year i n fi ve , frequency of occur­rence of open water and of concentrati ons of two tenths i ce or l ess , i nformat ion on the proporti on of o l d fl oes wh i ch shou l d be expected , the extent of r i d gi ng , an ana l ys i s of fl oe s i ze and of autumn i ce bu i l d-up are a l l avai l a bl e i n map and tabl e form . These reports can be purchased separatel y from the FENCO offi ce i n Cal gary . *

The fo l l owi ng ana l ys i s i s paraphrased from thei r reports and i s ba sed on a breakdown of the southern Beaufort Sea i nto s i x s eparate areas i n whi c h i ce cond i ti ons are fa i rl y un i form. These areas are numbered and separated by das hed l i nes i n F i gure 1 .

5 . 1 . 1 Med i an I ce Cond i ti ons

The i ce begi n s to c l ear north of Cape Bathurst i n t he second ha l f of May and i n the southern part of Mac kenz i e Bay i n m id­June . The l andfast i ce has u s ua l l y d i sappeared by J u ly 9 and by the end of the month the i ce concentrat i on i s l es s t han one tenth i n t he ent i re area from Herschel I s l and to Cape Kel l ett on Banks I s l and. M i n i mum i ce cover exi s ts on 1 7 September , then concentrat i ons r i s e to four tenths over the ma i n area by 1 5 October and to seven tenths by 2 2 October ( See Append i x I I ) . The vari at i on of the med i a n c l eari ng date and of the med i an freeze-up date through t he area anal yzed are s hown i n F i gures 8 and 1 1 .

* 301 Petro Chemi ca l Bu i l d i ng - 805 , 8th Avenue S . W., Cal gary , Al berta.

':A '20(,'2..-- go � \

74,· �-------r\-------tI-------tI-------t-------4I-------l-------1\05 I • .17.1 'JaN

I

t� .'lL- !�I;J9 15&

I I

."7 o �n � ? . � '

1

I ... • 'SO '...: �5. 1

• J14 � I .. , I - ::.. I K �� :-t "'. --.. .'tOO

.... 1 ". .. 2� �t.42 1 .'�l'� ,." -i 'I � ..

73°

12-

.93�� �111 � 7·�� .b-�" I

til " 94 _ �' -' � 2� . 1'4� . �. "'2 - "" t �4i2 J

. .128 US

" . 9'5 I , " '�I�. � .113 129 I

• tl3 96 I ., .\46

" • . :...J, lIoi � ,." I <S:I . - O'� �I

� 2' 134 <

< <

� )- � �' In, � rr

" :�" !�:7i>,:rl5'::::,;,\::::: �5\..>"\ '�64';';:.:I 1" l' �i .. - ' (:"" . 16�

'- ' I �)O 117 5 " ,G ." r � - ll! '- 4 � . ," ,,-.. -I. ' 1, " "e -', , , .. " ' ....

",,' " . 5 0" " ,0 �6" "!,,, 'r- -.� I ... 4 ._.6"" ��'I}� � ,,"'-e}11 3 .I�� !ISO\ ",-e16�

2 "'-- i , ". , "ii' �77 r 'h,>.! . • 06' I .. .;S� 1m " � �. "-

,.. ':::,.r"_':t :-..'J ,,y-; �T� - 'lI) ' i o" !" !,,:}'"",,-1"X�" ,, � � .,101 ' i,w''-<.-o "- f" .' '''' '7,

._ o r- - IT " • 0'" & -:;,,,,-,,,tl6 -I. ' ,,'. J" " !i9 � . ' .'35 " .'52 "

0 0 I, . _ .� .l!..-�,. �.;f'r�� ':eO) , "l'or )& . 0"'... " ,; ",,, 1, �.167 "-

_� • J6 1 " ..:: - ;, 1 .�. or'- 't7 "" . • 10' .� , ,,.53 .J"' ''

I .. . ".>0 . .. I I 2 .. --- 0 ' . " 137"'--'1 '" "-

AlA •• A , " � �...... II ..., ..!,. .,. .5 ,.,! '04 " >- 'i'� .:::-- .'''? .

, '- I " / 0 " .ar � .

.'" 17

11°

." :':.2 '"

I

r--t---t--=--�� �

.15'

YUKON .l3

L, NORTHWEST

&:l � TERRITORIES

Loca ti on s of the r-I)" ""

, . '

1420 140·

F i gure 1 .

1330 130· 1'28. 1126" I U data poi nts used i n the ana lys i s of week ly h i s tor i ca l i c e c harts .

..j:::.

5 . 1 . 2 Frequency of Occurrence of Various I ce Concentrat ions

The frequency of occurrence of var ious i ce concentrat ions i n percent for eac h of the s i x s ub-areas , s hown i n F i gure 1 , i s i l l u s trated i n F i gures 2 to 7 . Us i ng these frequenc i es i t i s pos s i bl e to est imate the expected operati ng s eason i n each of the s i x s ub-areas . U s i ng the bas i c data contai ned i n Vol ume I I of the FENCO report i s i s pos s i bl e to refi ne these fre­quenc i es for a s pec i fi c s i te . The vari at i on i n the med i a n l ength o f the operati ng s ea son (when i ce concentrati on i s under two tenths ) i s s hown i n F i gure 1 2 . �1i d - season i nter­rupti ons due to i ce i ntru s i on s are not i nc l uded on t h i s chart .

5 . 1 . 3 Best Ice Year i n F i ve

I n "good " i ce years rather extens i ve open water i s a l ready present i n Amundsen Gu l f by 2 1 May and a l though the fa st i ce i s s t i l l i n po s i t i on at the t ime , cl eari ng i s rapi d . I n Mackenz i e Bay the concentrat ion fa l l s to l es s than one tenth by 1 8 June . Th i s cond i t i on s preads over the enti re area by ear ly J u l y and open water rema i ns unti l mi d-October . Freeze­up i s then fa i r l y rap i d d ur i ng l ate October a l t hough the i ce i s t h i n . The var i at ion of the c l eari ng date i s s hown i n F i gure 9. Freeze-up dates are s imi l ar to tho se s hown i n F i gure 1 1 .

5 . 1 . 4 Worst Ice Year i n F i ve

I n Ilbad " years the i ce concentrat i on rema i ns at seven tenths or more unti l mi d-Augu st except i n s ha l l ow water areas wi th i n th i rty na ut i ca l mi l es o f s hore from Herschel I s l and to Cape Parry. t�i n imum i ce cond i t i ons by m id-September extend thi s c l eari ng to s i xty m i l es offshore but refreezi ng beg i ns by 1 October and exten s i ve i ce i s present by mi d-month . The var i at i on of the cl ear i ng date i s s hown i n F i gure 1 0 .

5 . 1 . 5 Number and Timi ng of I nterrupt i o n s

Other factors important to s h i ps , bes i des t h e tota l l ength of the operati ng s ea son , are those i n terva l s duri ng the s ummer when i ce i ntru s i ons occur . Al though these cannot be pred i cted more than a few days i n advance , i t i s i nteresti ng to know what has happened i n the pas t . The F ENCO report provi de s a deta i l ed ana l ys i s of i ce i ntru s i ons at a se l ecti on of the 1 70 data po i nts s hown i n F i gure 1 , but there are a few broad con­c l us i ons wh i c h can be reac hed regard i ng the durati on , t ime of year and numbers of i ntrus i ons wh i c h have occurred i n the past . These wi l l be touc hed on l ater .

Typi ca l res u l ts of a F ENCO geograph i ca l data poi nts ana l ys i s are a s fol l ows for po i nt #31 a t 696 30l N 1 37 °W .

Seas on Durati on

6

TABLE 1

#31 at 69° 301N , 1 37 °W BEG I NN I NG OF THE OPERATI NG SEASON - Ice Concentrati on two

tenth s or l ess

May J une J u l y 2 1 28 4 1 1 1 8 25 2 9 1 6 23 30

Number of Occurrences 0 0 0 0 6 3 2 4 3 2 1

% on or Earl i er 0 0 0 0 28 42 52 7 1 85 95 1 00

The fi rst row l i s ts dates i n one-week i nterva l s when the i ce concentrat i on decreased to two "tenths or l es s at the beg i n ­n i ng of t he season . The second row s hows how often t he sea son has opened on t he date immed i ately above and t he t h i rd row l i s ts the probab i l i ty i n percent of havi ng the sea son open earl i er . For examp l e there have been three years when the operat i ng sea son opened on 25 J u ne and t here i s a 42% proba­b i l i ty that the sea s on wou l d open on or earl i er than th i s date at the parti c u l ar data poi nt . The med i a n i n th i s and the fol l owi ng tabl es i s underl i ned .

TABLE I I

#31 at 69° 301N , 1 37 °W LENGTH OF THE OPERAT I NG S EASON

In Weeks 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 19 20

Number of Occur-rences 2 0 0 1 1

% S horter

2 1 3 1 1 2 2 2 2 0

Sea son 0 4 1 4 1 4 1 4 1 9 23 33 38 52 59 6 1 7 1 80 90 1 00 I n th i s tabl e the f i rst row i s mere ly a numeri cal l i st of the pos s i b l e durat i ons i n weeks between the beg i nn i ng of the sea­s on when t he i ce c oncentrat i on becomes two tenths or l es s and the end of the sea son when i t i ncreases above two tenth s . Ice i ntru s i ons duri ng th i s i nterva l are s ubtracted . The second row i nd i cates the number of years when a g i ven dura­t i on has been observed ; i . e . a sea son of 1 1 weeks durati on ha s occurred twi ce . The th i rd row i s the probabi l i ty i n per­cent of havi ng a s horter sea son; i . e . there i s a 23% chance of havi ng a sea s on s horter than 1 1 weeks .

7

TABLE I I I

#31 at 6 9° 301N , l 37 °W I NTERRUPT I ONS DUR I NG THE OPERAT I NG SEASON

Number of I nterrup-t i ons a 2 3 4 5 6 7 8 9 1 0

Occurrences 7 8 3 2 a a a a a a

% Occur­rences 33 71 85 95 1 00 1 00 1 00 1 00 1 00 1 00 1 00

Th i s tabl e focusses on those per iods when the concentrat i o n ri ses above two tenths i n the i nterva l s i n the fi rst tab l e , whi ch were su btracted from the tota l l ength of the season. The fi rs t row l i sts the pos s i b l e number of i nterrupti ons , the second presents the number of t imes that a fu l l summer season ha s had a spec i fi c number of i nterrupti ons and the thi rd row i s the probabi l i ty of havi ng a season wi th fewer i nterrupt ions . For exampl e there have been seven s ummers wi th no i nterrupti ons , 8 seasons wi th one and there i s thus a 3 3% c hance of havi ng no i nterrupti ons and a 7 1 % chance of hav i ng l es s than two .

TABLE I V

#31 at 6 9 ° 301N , l 37 °W DURATION OF I NTERRUPTIONS DUR I NG THE OP ERATI NG SEASON

Total Durat ion of I n terrupt i on I n Weeks a 2 3 4 5 6 7 8 9 1 0

Number of Occurrences 7 4 4 4 0 0 0 a a

% Shorter 33 5 2 7 1 9 0 90 95 1 00 1 00 1 00 1 00

I n th i s tabl e the tota l t ime l o st duri ng the operati ng season i s treated , i n effect a s ummation of the number of t imes that i ce i ntruded and i ts effect on the operati ng program . The fi rs t row l i sts the poss i b l e total durati ons , the second the number of t imes they have occurred and the t h i rd i s a cumu l a­t i ve percentage probabi l i ty of havi ng a sea son wi t h bri efer peri ods of i ce i ntrus i on .

r�umber of Occur-rences

% Later

8

TABLE V

#31 at 69° 3 1 IN , 1 37 °W END OF OPERAT I NG S EASON

August 6 1 3 20

0 0

95 95 95

27

0

95

September

3 1 0 1 7 24

o 1 2 0

95 90 80 80

October

1 8 1 5 22 29 Later

2 1 2 2 2

7 1 66 57 47 38

8

The fi na l tabl e presents the �ates on wh i c h the i ce concentra­t i on rose above two tenths and rema i ned so , the number of t imes i t has happened on a parti cu l ar date a nd the percentage proba­b i l i ty of hav i ng a l ater end to t he season . For exampl e , i n one year the season ended o n September 1 0 , the s econd earl i es t on record and there i s thus a 90% proba bi l i ty that t h e e n d wi l l occur l ater than th i s date .

The FENCO report l i s ts e l even d i fferent l ocat ions i n the above format but genera l i zat i ons are rather d i ffi c u l t to make. At fi rst one wou l d expect that the number a nd durati o n of these i nterrupt i ons wou l d i ncrease wi t h the d i s tance from s hore but thi s i s on ly part i a l l y true. In some cases , the open i ng of a pol ynya outs i de the fas t i ce creates an earl y s tart to the operati n g season but l ater , break-up of the fas t i ce resu l ts i n i ntrus i ons at a t ime when outer s i tes wi l l reta i n p l ent i ­ful i ce cover . If th i s pecu l i ari ty i s ta ken i nto account a l onger un i nterrupted season i n coastal waters becomes apparent . I ntrus i on s are mos t common i n the mi ddl e d i s tance from shore where the pack may advance and retreat a num-ber of t imes duri ng the s ummer . I n even deeper water , the greater decrease i n the l ength of the operat i ng s ea son i tse l f means that i nterrupt ions are fewer and wi l l l ast l onger s i nce average i ce concentrat i ons are h i g her .

5 . 1 . 6 I ce Zones

In the southern Beaufort Sea there are three i ce zones whi c h vary i n s i ze from season to season and from year to year . The f i rs t of t hese i s the fas t i ce zone a l ong the cont i nen ta l c oast and on the west coa s t of Ban ks I s l and. I ts s eaward l imi t i s c l ose to t he 20 metre i sobath and can norma l l y be i dent i f i ed by the a bu ndance of r i dges , the c hange to seaward of i ce concentrat i ons from ten tenths to l es ser amounts and the presence of open water l ead s , depend i ng on wi nd condi t i o n s . There i s usua l l y a r i dged i ce zone a l ong the edge of t he fas t i ce where h i g h ly deformed i ce i s created by pressure from mov­i ng pack further offs hore and the g round i ng of fl oes .

9

-yt=t-=f::-=="±:--t----·-··---j--------i-.+

--�.2 ----�------- .-I

80� L.U U Z L.U a.:: 0::: 60 ::::> U U o u.. o

40 >­U Z L.U ::J o ill ---+-------li---..-:�-_\t_� 20 e:

o

FI GURE 2 . TOTAL I CE CONCENTRATI ON - AREA 1

The coas tal area of Mackenz i e Bay i ncl udi n g data poi nts

1 5 , 2 2- 2 3 , 30- 33 , 4 1 - 4 3 and 51 ( F i g ure 1 ) . Cl eari n g i s ea rly and i n mos t s eas ons nearl y comp l ete. There i s onl y a s l i gh t vari ation i n condi ti ons from N orth to S outh i n t he area .

J

14 21 ;<1 4 il �3 tl/ .. ,' JUf'lt

1 0

80 oe L.LJ U Z L.LJ 0<: 0<: '-t-;--+-t-----+-i 60 :::>

, , I I I I 1 .; I ! : I

40

U u o LL o >­U Z w ::J C w

+---\\-+----l'� 20 �

r.; ;0 :�'j �.J o · iJ '�.j 2"7 �� �\J 1/ /.1 I JUL'( /\uc;usr ':,If'l tM:3c:K

DATE

FI GURE 3. TOTAL I CE CONCENTRAT I ON - j\REA 2

The coas tal area from Ri chards I s l and to Cape B ath urs t and the enti re area of Frank l i n B ay - data poi nts 57 58 , 6 4 6 5, 7 1 7 2 ,

80 , 89 90 , 1 0 2- 1 0 4 , 1 20 , 1 55 1 56 &1 70 ( F i g ure 1 ) .

Th i s i s es sent i a l ly the fas t- i ce a rea where cl ea ri n g i s i n i ti a l ly s omewhat de l ayed b ut then progresses rapi dly i n J u ly . C l eari ng i s

j us t as cons i s tent as i n Area 1 b u t i s s l i gh tly l ate r i n deve l opi ng.

1 1

w U Z w Or:: Or:: �--�--�----+-----���--��--�-------+r-�.-�� 60� U U o u... o

�--�------�+------.f-�--------r--------+--1-�--�40� WATER u z w :::>

o w --+---------�------_4----4_�_+� 20�

14 21 28 4 MAY

FI GURE 4 . TOTAL I C E CONC ENTRAT ION

o

AREA 3 The ne ar offshore area from Ri ch ards I s l and to C ape Bath urs t

and C ape Ke l l ett i nc l udi ng the appro aches to Amun ds en Gul f . D at a

poi nts i ncl uded are 48 , 56 , 6 2 6 3 , 69 70 , 78 79 , 87 88 , 99 to 1 0 1 ,

1 1 6 to 1 1 9 , 1 32 to 1 3 7 , 1 48 to 1 54 and 1 6 3 to 1 6 9 ( Figure 1 ) .

The format i on of offshore polyny as res u l ts i n an e arly decre as e i n i ce cover b ut cl e ari ng p rogres s es s l owly from early J une

unti l e arly September. The frequen cy of comp l ete cl e ari ng is l ower t h an i n e i ther Are as 1 or 2 .

� . ..... �; f : . '- < .

12

w U Z w '"

�L-�--------+-��===-+-------��'-------4--+---�-+�60�

���----��+---�----+-------�r--------����--4+-i40

u u o u.. o >­u Z UJ :::) C w

�---+-+------�--------��-------�-------4-+��--�rl 20�

14 21 2B 4 II le MAY JUNE:

FIGURE 5 . TOTAL I CE CON C ENTRAT ION

o

AREA 4

The offs h ore are a from Hers ch e l I s l and to t he west co ast

of Banks I s l and. D at a p oi n ts i ncl uded are 3 , 4 , 7 , 8 , 1 3 , 1 4 , 19 to 21, 2 8 , 29 , 37 to 40 , 46 , 47 , 49 , 50 , 5 3 to 55 , 60 , 6 1 , 6 7 , 68 ,

76 , 7 7 , 85 , 86 , 9 7 , 98 , 112 to 1 1 5 , 1 28 to 131 and 1 44 to 1 47 . C l e ari ng i s much l es s common th an i n i ns hore areas b ut the re i s a

l engthy p eri od when the i ce i s wel l di spers ed .

1 3

-------+---------4----�----��80� r,.

; ,

\ ---+t-----l \

. 1��·5 __

�--+-----+----� .,r .. - _ . . -_... . . , . \\ ,

LlJ U Z LlJ Q:: Q:: 60 :::> u u o LL o

40 >-­U Z LU :::> o LlJ

��--4_--------1_--------���--�� 20�

FIGURE 6 . TOTAL ICE CO NC ENT RATION - AREA 5 The deep w ater are a where the fri nges of the Arcti c P ack

are us u al ly pres ent. Data poi n ts i nc l uded are 1 , 2 , 5 , 6 , 9 to 1 2 ,

34 to 36 , 44 , 45 , 52 , 59 , 66 , 7 3 to 75 , 8 2 to 84 , 94 to 96 , 1 09 to 1 1 1 , 1 25 to 1 27 , 1 40 to 1 43 , 1 58 and 1 59 ( Fi gure 1 ) .

C l e ari ng or even di s pers ed i ce i s uncommon i n th i s are a but the

trend for s l owly i mprovi n g i ce condi ti ons from May to mi d September

i s evi dent .

1 4

------r--------1---------+--------� 80� o �_..J_. .. �-...... -- ... - _ .

. ,' '" w �-++-I----i' --_-+------+---'-'�-,-.,---+---4 60 I �.8 I

j --�------·--�------�----+---_r,40

u. o >­U Z w ::::> o ill

-�-+---:::::;;&"=- �----+--I 20 3:

o

FI GURE 7. TOTAL I CE CON C ENTRAT ION AREA 6

The northern offshore are a wes t of B anks I s 1 and . D ata poi nts i nc l uded are 81 , 92 , 9 3 , 1 0 5 to 1 08 , 1 21 to 1 24 , 1 38 and 1 39 .

( Fi g ure 1 ) .

B ri ef i ce di s pers al s c an occ ur i n th i s are a at any t i me d uri ng the s ummer b ut conges ted condi ti ons are us ual l y p res ent .

+-

I' r .VI'" I ' I , '

,

,.­'i

.' I '-i-­!

t

T i-

. MEDIAN CLEARING DATES ?ItO ICE DR LESS

T

·......--+-----.. -t- ..

Figure 8 . Map of Median Clearing Dates - 2/10 ice or less.

, JU\LY 2.

�� " , � r-

" \

."�l : ,}\::J � ..---->"" .!, ,J \ ""�_;} �Cc)t -\

" ?:, " �>;;-; � ,--� J i:Yz ' l' ,-

\ ,-

-' (J1

I �

t�

\ -\

1 6

\ --+�---(

i I -r

�

Vl Vl OJ �

>-0 OJ U

'r-

0 � -.. N

L!) c

'r-

'r-u..

• CI,.EARiNG -dATE i<WORST yeAR IN 5) i 2;10 ICE oR LjESS"

!

/

r- '

",

V<'i. t-ccr rL�-� -figure 10. Map of Clearing Date (Worst year in 5) - 2/10 ice or less.

- "\"" -.1, - _ _ c "

.. , '-". (

� C--. ,

--+�->� �� " "':'1 "\ ::'//�;,.:/,:

, � >'1.

\ "

,'/ .. �,+ ' \ 1 --;;'(;':1 ' i - , >i-.. _ \ 1_�, l • 1. ' . � I.

\ ,\ , / :,/,. �\ �--l_ '

....... -..I

.--;--

--\��� -:=�--:-t---�-- -------;--r-\ ---;:--- �\------------, " \

, M£J)I�N FRE�lr-Up DATE! \ -� -�.

I ,, - ! -1--/-p/OV£R 2 TENTHS ICE

./ i OF ANY THICKNESS [' / /

i t·/

- i -_/

Fi gure 11. Map of Median Freeze-up Date - Over 2/1 0 ice of any thi ckness .

-�-

.,:1:1 '\ < -

" .. '1-f� .

,. :,>��'S:p�:: D< -:\ "'

--' co

-t

-I-. �

-- { '-- T MEDIAN N(vMB£R OF WEEKS -r lN OPERATING SEASON (UNDER E TENTHS OF Ie £) ,E.XqUDllt§ INt£RRUP7'lONS ' /_ ' IOF I WEtK i , _ ' __ '_+ ___

t-

. �/ . " I ";:

' ," "," , .

�. ' / 6 I . . '. " , .=- ., ' �J _ �

, . .

�� �' . dr- "

! -r- ,--__ '��" =- _< , '. , '. _ . . ,

Figure 12, Map of Median number of weeks in Operating Season _ under 2/10 of ice,

-t" "

(

( '-D

'. J

20

The second major zone is a part of the drifting offshore pack ice where first-year ice predominates during the colder part of the year and where open water conditions may develop pro­gressively during the melting season. This zone is characterized by variable ice concentrations, floe sizes and ice thicknessess. It also varies in extent from season to season and from year to year.

The third major zone is also within the offshore pack, but there old ice is predominant and the changes in ice concentra­tions and ice thicknesses are somewhat restricted. The position of the boundary between Zone Two and Three is vari­able and is dependent on the gross movement of the Arctic pack itself. In most years this third zone lies near the northern limit of the study area and in the offshore area west of Banks Island. In the "worst" ice years, old ice can be driven to the offshore boundary of Zone One because of persistent onshore winds such as those of 1974 . Melting of the first-year ice in Zone Two is a prerequisite for a major invasion of old ice.

5.1.7 Autumn Ice Build-Up

In autumn, the termination date of offshore drill ship opera­tions at most sites is related more to ice growth than to intrusions of the Arctic pack from the northern Beaufort Sea. There are two problems here, one being the probable ice condi­tions at the drilling site and the other, ice conditions on the exit route or at an overwintering site, assumed to be in the Beaufort Sea. Access to dri 11 i ng sites in the spri ng from Beaufort Sea harbours can be achieved earlier than is possible from locations west of Point Barrow, and retreat from the sites in the autumn can be delayed somewhat longer since freeze-up is later in the southeastern Beaufort Sea than it is off Point Barrow.

From charts of median ice concentration (Appendix II) it is apparent that the formation of ice away from shore is some­what slower than in the shallow coastal waters. It follows that ice conditions at an overwintering harbour will control the termination date of drilling operations rather than ice conditions at the drilling site or en route from it.

Good temperature records and ice thickness measurements are available for Sachs Harbour and Cape Parry and from Tuktoyaktuk to a lesser extent. From an analysis of these date the median freeze-over date at Sachs Harbour is 12 October and at Cape Parry 20 October. Thirty percent of the freeze-up dates are within 10 days of this date at Sachs Harbour and within five days at Cape Parry.

The median date for the growth of 30 cm of ice at Sachs Harbour is 27 October. Up to this date, there is an average accumulation of 380 Freezing Degree Days (Celsius).

21

Th i rty percent of t he d ates l i e wi thi n 2 days of th i s med i a n . The med i an d ate for 30 cm of i ce growth at Cape Parry i s 3 1 October after 270 Freez i ng Degree Days h ave accumu l ated . Th i rty percent of the d ates l i e wi th i n 3 days of the med i an .

A t Tuktoyaktuk the med i an d ate for 3 0 cm o f i ce growth i s 4 November after 305 Freezi ng Degree Days h ave occurred . Th i rty percent of the d ates l i e between 2 and 5 November . No i nterpol ati on of freeze-over d ates h as been attempted at th i s s i te because the run-off from the Mac kenzi e Ri ver h as a great i nfl uence on the i ce formati on i n the bay.

It i s app arent that ces s at i on of offs hore operati ons us i ng dri l l i ng ves sel s s hou l d be p l anned for mi d-October. Thi s con­c l u s i o n i s not greatl y d i fferent from what one wou l d expect from a s i mp l e cons i derat ion of -the offshore i ce cond i ti ons s hown i n F i gures 2 to 6 .

5 .2 A Study of the Mot ion of I nd i v i du al Ice F l oes i n the Beaufort Sea

5.2.1 I ntroducti on

I n i ti al l y offshore expl oratory dri l l i ng i s a s ummer season operat ion and hence there i s an obv i ous need for expl i c i t i ce forec asts for the area of operat i on s . At present� the C an ad i an i ce pred i c t i on serv i ce i s des i gned to prov i de adv i ce to co astal s h i pp i ng duri ng res upp ly operat i o n s � and as a res u l t refi nements i n d ata col l ecti o n � d ata analys i s , d ata del i very and i ce pred i ct i ons are needed . I n part i c u l ar the pred i cti on tech ni q ues themsel ves mu s t be improved u pon .

Wi th these requ i rements i n mi nd , an an al ys i s of the mot i on of s pec i fi c i ce fl oes was undertaken to provi de add i t i onal exam­pl es of both the mean and extremes of i ce mot ion t hat may occu r . Images from ERTS are avai l abl e for both the 1 97 3 and 1 974 seasons and from t hese i t i s po ss i bl e to p l ot t he tracks of i ce fl oes for two or t hree days when i mages from over l ap ­p i ng orb i ts were suffi c i ent ly c l oud free . I n one c ase a fl oe cou l d be i denti fi ed on consecuti ve cycl es and i ts total move­ment over an l S-day i nterv al was p l o tted .

Further i nformati on on the dri ft of i nd i v i d ual fl oes was obt ai ned i n the s ummer of 1 974 duri ng a surface current study ( Garrett and MacNe i l l 1 976 ) where rad i o beacon s pl aced o n fl oes i n t h e near-s hore are a were trac ked by f i xed wi ng ai r­craft. The dri fts of these fl oes h as been rel ated to wi nds deri ved from atmospheri c weather c h arts .

5 .2 . 2 S atel l i te Imagery

5 .2.2.1 Avai l abl e Data

Marko and Gower ( 1 974 ) exami ned the dr i ft of fl oes i n the s ummer of 1 97 3 and i n p art i c u l ar c ases p l otted

22

thei r dr i ft i n mi d-June , earl y Ju ly and l ate Augus t . The i r reported accuracy of l ocat i on was estimated at 1% of the d i stance from s hore , hence for further s tud i es ba sed on thei r work one i s l imi ted to those cases where the rate of moti on was s uffi c i entl y l arge to perm i t rea s onabl e est ima tes of both d i recti on and rate of actual dr i ft . An added s tep i n th i s analys i s i s to rel a te the i c e mot i on pl otted to the meteoro­l og i ca l c ond i t i ons at the t ime .

One of the procedures used i n I ce Central * i s t o pre­pare a da i l y mean surface- pressure c hart from wh i ch mean da i l y wi nd vectors can be deri ved . For the past few years , the charts have s hown contours of the he i ght of the 1000 mi l l i bar pressure surface . The s pac i ng and ori entati on of the hei g ht contours a re c l ose ly rel ated to surface wi nd cond i ti ons .

Add i ti onal fl oe d r i fts were exami ned u s i ng Qui k100k ERTS imagery for the days 15 to 16 , 16 to 17 , 17 to 18 and 18 to 19 of J une 1973 . On l y those images s howi ng coastl i nes and i dent i fi abl e fl oes i n the same frame were used . Off Cape Bathurst , resu l ts s howed a med i an defl ect i on ang l e of +16 ° a nd a med i an ice dri ft to w i nd speed rat i o of 0 . 0262 , wh i l e i n the Cape Kel l ett area the med i a n defl ect i on angl e was 47 ° for f i ve d i fferent fl oes and the med i an speed rat i o was onl y 0 . 0106 . I n the l atter area , water current from the s outhwest probab ly exi sted .

Imagery obta i ned duri ng 1974 was exami ned a t Ice Cen­tral to obta i n more exampl es of the dr i ft of spec i fi c i ce fl oes . Unfortunatel y , the season was a severe one w ith the pac k rema i n i ng near s hore throug hou t the summer and free d r i ft of rel at i vely i s ol ated fl oes rare ly occurred . The exampl es l i sted i n Tabl e 1B were obta i ned but i n mos t cases these repre­sented fl oes whose dr i ft was affected by other i ce i n the v i c i n i ty .

5 . 2.2 . 2 Ana l ys i s

There i s l i tt l e quant i tat i ve data that can be deri ved from Tabl es 1A and 1B but the i nternal c on­s i s tency l eads to s ome i nteresti ng q ua l i tat i ve concl u s i ons . Fl oes A , B and C (F i gure 13 ) moved at c omparabl e speeds and had s i mi l ar deflecti on angl es u nt i l J une 19-20 when t he defl ect i on angl es abru ptly changed from 10° to 30 ° to the r i ght of the wi nd to 5 ° to 25° to the l eft of the wi nd wi t hout a s i gn i fi ­cant c hange i n the dri ft s peed . I t wou l d a ppea r e i ther a water current fl owi ng from northeast t o

*Ice Forecast i ng Central , Env i r onment Canada Trebl a Bu i l d i ng , Ottawa .

23

s outhwest was enc ountered or t he pl otted pos i ti ons are i n error . The fact the angl e wa s even greater dur i ng the per i od J une 20 to 21 (when only one fl oe was tracked ) i nd i cates that s i nce the wi nd di d not c hange much , e i ther the current i ncrea sed or an error i n pos i t i on i ng exi sted . I n v i ew of the d i stance from s hore and the c i rcl e of pos s i bl e error , the l atter· appears to be most l i kel y . F i gure 15 s hoes a day-by­day pl ot i n J une 1973 of Fl oe B .

Fl oes 0 , E and F ( Tabl e l A , F i gure 14 ) are another grou p whose dr i fts can be compared . Fl oe 0 fol l owed t he wi nd on J u l y 4 to 5 when i t wa s near t he shore , but then from J u ly 5 to 7 i t moved 75 ° to 80° to the r i ght of the wi nd a s i t dr i fted seaward under east­s ou theasterl y wi nds . A s outhwest to northeast current of 10 to 12 na ut i ca l mi l es per day must be a ssumed i f the same rat i o of i ce dr i ft to wi nd s peed conti nued from the prev i ou s day .

Fl oe F was s omewhat further from s hore but agai n l arge pos i t i ve defl ecti on ang l es occurred between 5 to 8 J u ly a nd i n t h i s case c ou l d have been caused by a current from s outh- s outhwes t fl owi ng at 10 to 12 naut i cal mi l es per day .

Fl oe E was much further east and had a sma l l defl ec­t i on to t he l eft of the wi nd wh i ch cou l d have been caused by a water outfl ow around the s outh end of Banks I s l and , a mot i on t ha t has been not i ced duri ng break-up i n other summer seasons . W i t h on l y two pos i t i on fi xes , n o quanti ta t i ve est imate of thi s cur­rent i s pos s i b l e .

Fl oes Gl , G2 and G3 ( Tab l e l A , F i gure 14 ) a l l observed i n the same 48- hour s pan , moved at comparabl e s peeds w i t h modest defl ect i ons to the ri ght of the wi nd vector .

I f a l l the dr i ft data are c omb i ned except where s i g­n i f i cant water currents appeared to have existed , the med i an defl ecti on angl e i s 2 2 ° to t he r i ght of the wi nd vector and med i an rat i o of i ce dr i ft to wi nd s peed i s 0 . 0337 . Both resu l ts fi t wel l i nto the range reported i n prev i ous stud i es g oi ng bac k to t he days of Nansen ( 1897 ) .

Tabl e 1B s h ows dr i ft data from ERTS imagery 1974 and i s to be compared w i t h Tabl e l A whi ch concerns 1973 imagery . t·1aj or d i fferences are immed i atel y apparent . The i ce dr i ft to wi nd s peed rati os are onl y one t h i rd of those found i n 1973 a nd the defl ect i on angl es , are extremel y vari abl e . I n 1973 , l arge free-fl oat i ng fl oes were stud i ed when i ce concentrati ons were s i x to e i g ht tenths . Those i n 1974 were i n c oncentrati ons

24

TABLE l A

ICE DRIFT INTERPRETED FROM ERTS IMAGERY IN JUNE AND JULY - 197 3 ;

AMUNDSEN GULF AND WESTERN BANKS ISLAND

Da tes Ice Vel oc i ty Vi Hi nd Vel oci ty Vw Speed Defl ecti on Ang l e

D i rec ti on S peed D i rect i on Speed Rati o Degrees to Ri g ht V' of Hi nd Degrees nm/day Degrees Knots -fw

Floe A Jun� 15-16 095 9 . 6 085 16 0. 0250 +10

16 -17 135 11 . 7 095 2 0 0. 0244 +40 17-18 145 9 . 0 115 23 0 . 0163 +30

Floe B June 15-16 110 17. 0 085 16 0 . 0444 +25

16-17 135 25 . 4 095 20 0 . 0529 +40 17-18 135 2 0. 0 115 23 0 . 0363 +20 18-19 125 17 . 0 115 18 0 . 0395 +10 19 -20 085 9 . 0 110 18 0 . 0 209 - 25 2 0-21 005 6 . 4 115 15 0 . 0296 -11 0

Floe C June 16 -17 145 12 . 7 095 2 0 0 . 0500 +50

17.,18 135 6 . 9 115 23 0 . 0125 +20 18-19 140 9 . 6 115 18 0 . 0222 +25 19-20 105 11. 1 110 18 0 . 0258 +20

Med i an s 0 . 0258 +20

Floe 0 Jul y 4-5 130 2 . 0 130 4 0 . 0386 0

5-6 185 11. 1 110 9 0 . 0097 +7 5 6- 7 185 10 . 6 105 8 0 . 0192 +80

Fl oe E Jul y 4- 5 120 17. 0 130 4 0 . 0333 -10

Fl oe F J u l y 5- 6 16 5 10. 6 110 9 0 . 0491 +60

6-8 140 10 . 1 105 7 0 . 0565 +35

F l Qe G 1 J u l y 8- 10 330 15 . 4 3 00 6 0 . 0201 +30

F l oe G2 Jul y 8- 10 310 18 . 5 3 00 6 0 . 0243 +10

Fl oe G3 July 8,.,.10 3 00 13 . 2 300 6 0 . 0174 0

Med i ans 0 . 0243 +30

25

TABLE l B

I C E DRI FT I NTERPRETED FROM ERTS I MAGERY OFF CAPE KELLETT I N

Dates

Fl oe Z July 1 7- 1 8

1 8- 1 9

Fl oe Y August 5 August 5- 6

Fl oe X August 25-26

.F1ow W August 25-26

Fl oe V August 25- 26

J ULY AND OFF TUK PEN I NSULA I N AUGUST 1 974

I ce Vel oc i ty V i D i recti on Speed Degrees nm/day

1 580 1 . 4 1 35 0 . 8

350 1 4 . 7 005 1 . 4

1 45 0 . 8

200 0 . 7

202 1 . 5

Wi nd Vel oc i ty Vw D i rect i on Speed Degrees Knots

1 4 5 0 6 2 1 0 6

085 44* 1 00 7

1 35 1 2

1 35 1 2

1 35 1 2

Med i an

Speed Rat i o V i Vw

0 . 0097 0 . 0056

0 . 0029 0 . 0081

0 . 0028

0 . 0059

0 . 0052

0 . 0056

* Res u l tant w i nd over 1 8 day i nterval

Defl ect i on Angl e Degrees to Ri ght

of w i nd

+1 3 -55

-95 - 95

- 1 0

+65

+65

- 1 0

26

r -/ \ \� 74°

I ; 1 i ! j i I I

, I I I I ! !

7.20 . I I I ! I I I

20 I I 70° '21 !/

. -.

.. . .. _

.. ) ...

1/

I I I

I I

I / /

I \ ! +- I _____ T---t - -"'-"'-"'-1 ----··-·)r-·- .. -.. - . \" I / \ l> 1 / ·

, I I / / . I

. __ . • .,1 O .. -".----.. .. ----'/ I II 21 I ' "" /: I . / i o /' I ··-iO l 20\ // 20� / I / ; l oe C /� I M

I /

I I / ....... _._------I I , l �18

... IH . �oe Fl oe 15 A ." -� 15B

I Cape �rry I

Fi gure 13. (After F i g . 3 a of Marko and Gower) T he d ai l y pos i ti ons of several i ce fl oes i n J une 1973 . T he u ncertai nti es i n the determi nati ons are represented by the s i ze of the ci rcl es i n each area. The das hed l i ne represents the edge of the congested porti on of the pol ar pack .

27

Fi gure 14. (After Fi g. 3 b of Marko and Gower) The d ai ly pos i ti ons of several i ce fl oes i n Jul y 1973 . The d as hed l i ne represents the edge of the c ongested pol ar pack i ce .

28

,1 cm represents 1 0 nm i ce dri ft 1 0 kts wi nd s peed

2 1 s

�, Wi nt .........

1 1 50 ,2 3 k ts

dri ft-1 35° ,2 0 nm

0lIl(.- _ _ 1 6 t� Ice dri ft -l l O� 1 7 nm Defl ect i on ang l e +250

�_- 1 5th �ind O{)85' ,1 6 kts

F i gure 1 5. Graph i ca l representati on of the d ri ft of Fl oe B . Ice vectors are s ol i d l i nes a nd a s soc i ated wi nd vectors are das hed l i nes . Days i nd i cated are i n J une 1 973 .

29

greater than n i ne tenths so there was a s i g n i fi cant effect on one fl oe by another . As a resu l t the data i n Tabl e l B i s n ot d i rectl y u seful i n the study of wi nd dr i ft of i nd i v i dua l fl oes but i t does i nd i cate the trend i n rates of dr i ft occurri ng when i ce con­centrati ons are h i g h .

5.2. 3 Dri ft Buoys and Beacons

5.2.3 . 1 Data Ava i l abl e

Add i t i onal i ce dr i ft data were obta i ned from a Beaufort Sea Study concerned w ith the measurements of s urface currents (Garrett a nd MacNei l l 1976 ) . Because the i ce rema i ned c l ose i n- s hore d uri ng the s ummer of 1974 i t was pos.s i bl e to exami ne the dri ft of a few i ce fl oe s tagged with radio beacons and tracked by a f ixed-wi ng a i rcraft . D i rect fi el d meas urements of fl oe mot i ons were rel ated to actual wi nds a s wel l a s to those deri ved from mean da i l y pressure charts .

Tabl e I I s h ows the deta i l ed dri ft of one i ce beacon . The rema i nder are l i s ted i n Append i x I .

5.2 . 3.2 Anal ys i s

The ori entat i on a nd s paci ng of contour l i nes on the 1, 000 mi l l i ba r hei ght chart i nd i cates t he geostroph i c wi nd vel oci ty a t that l evel . Because of fri c ti on , surface wi nds are defl ected to t he l eft by about 25 ° and s peeds are s omewhat reduced , t he amount be i ng dependent u pon the s tab i l i ty of the a i r , the rough­ness of the terra i n and other factors . When i ce mot i on i s be i ng stud i ed , one can fi rst c ompa re the d i s pl acement of an i ce fl oe i n rel at i on to the s ur­face wi nd dr i v i ng i t and a l s o compare the i ce dri ft vector deri ved from the press ure chart depi ct i ng the meteorol og i ca l cond i ti ons at the t ime . Th i s i s the procedure fol l owed i n mos t i ce forecast i ng work for pred i ct i ng s urface wi nds from synopt i c and prognost i c weather maps and i s used to forecast the i ce moti on duri ng the ens u i ng per i od .

I n Tabl e I I , the med i an s peed rat i o of the wi nd a nd i ce mot i on and the defl ecti on a ng l es fi t qu i te rea s on­abl y i nto the previ ous data l i sted i n Tabl e I . I n Tabl e I I , wi nds deri ved from the mean 1 , 000 mb he i g ht charts are compared wi th i ce dri ft . S i nce i ce moves to the r i ght of the wi nd and t he w i nd i tsel f i s defl ected to the l eft of the contour l i nes by a s imi ­l ar amount , very smal l defl ect i on a ngl es are expected . I n th i s case the med i an wa s only 5 ° , c l ose to the l imi t of accuracy of the wi nd determi nati on .

TABLE I I

MOTI ON OF DRI FT BEACON #1 NEAR 70° 30 ' N , l 33°W

Dates Ice Vel oc i ty V i Deri ved Wi nd Vel oc i ty Vw Speed Rad i o Defl ecti on D i rect i on Speed Di recti on Speed V i Ang l e Degrees

Degrees nm/d ay Degrees Knots Vw to Ri ght of

W i nd

Jul y 14- 15 075° 1 . 7 090° 12 0 . 0057 -15° 15- 16 100 1 . 7 100 12 0 . 0079 0 16- 17 133 2 . 0 145 10 0 . 0080 - 12 17- 18 3 13 1. 0 2 10 9 0 . 0045 +103 18-20 313 4 . 5 010 10 0 . 0096 -57 2 1-22 110 1. 0 115 6 0 . 0067 -10 22-24 103 6 . 0 090 16 0 . 0071 +13 24-25 103 3 . 5 ( L i ght and v ari abl e ) w 0 25-26 346 0 . 3 ( L i ght and var i abl e ) 26- 27 160 1. 5 ( L i g ht and v ari abl e ) 27- 29 2 10 0 . 3 215 6 '0 . 0028 - 5 29- 30 2 10 2 . 0 180 12 0 . 0056 +30 30- 3 1 238 1. 0 125 9 0 . 0046 +113 3 1-02 308 5 . 5 035 11 0 . 0108 -87

Aug . 02-03 115 4 . 5 ( L i ght and var i abl e ) MEDIAN 0 . 0067 - 5

31

Some anoma l ous defl ect i o n angl es observed wi th i n the two week per i od need further exami nati on . On J u l y 17 to 18 there was a deepi ng l ow wes t of Tu ktoyaktuk wh i c h s ubsequent ly moved across the Beaufort Sea to Mel v i l l e I s l and . In th i s case the deri ved w i nd wa s rel ated to the overa l l c i rcul at i on around the centre of a devel opi ng l ow wh i l e the i ce mot i on resul ted from stronger wi nds whi c h occurred after the pas sage of the centre . The observed wi nd reported by Garrett and MacNe i l l (1976 ) at the beg i nn i ng of the i nterval between fi xes was 180° at 6 knots . A Istorml wa s menti oned at th i s t ime i n the i r report so i t i s expect­ed that t he i ce dr i ft wou l d fol l ow the s tronger wi nd d i rect i on . A defl ecti on ang l e of 57° to the l eft of the wi nd occurred s im i l ar ly i n the s ubsequent 48-hour per i od . Obv i ous l y spec i a l procedures s houl d be devel o ped for forecast i ng the mot i o n of fl oes i n a reas c l ose to devel opi ng mi gratory l ow pressure centres .

Major vari a t i ons i n the d i rect i o n of the dri ft a l so rose i n the peri od J u l y 31 to August 3 when another m i gratory l ow deve l o ped . The d i rect i o n of offs hore i ce dr i ft d i d not appear to be rel ated to vari a t i ons i n meteoro l og i ca l cond i t i ons on J u l y 3 0 to 31 u n l ess a water current from wes t to east i s a s s umed . The deri ved wi nd averaged over 48 hours from J u l y 31 to August 2 a l s o i nd i cates that a wes t to ea s t water c urrent exi sted .

Beacons #3 and 4 were trac ked at rough l y the same t ime and i n the same areas as #1 wh i l e Beacon #2 was l ocated a few degrees of l ong i tude further west (Append i x I ) . Large defl ect i o n angl es and unusua l s peeds occurred a t the t ime for a l l these fl oes and i n every case the expl anations are s im i l ar.

Another group of beacons was pl aced on t he i ce i n the l atter ha l f of August near l 35°W (#4A , #5 , a nd #6 ) a nd a s i ng l e one near 137°W . I n most cases , the dr i ft rates were noti ceab ly h i g her than i n J u l y a nd t he defl ect i on a ng l es at l 35°W were extremel y vari abl e. On the f irst day of the dri ft , the three beacons near 135°W a l l moved eastnorthea s t under a northea st w i nd , consequent ly water currents rather than wi nds a ppeared to control the dri ft pattern . Northwester ly wi nds had been bl owi n g for e i ght days pri or to the date . Garrett and MacNe i l l (1976 ) reported t hat i n th i s area a southwest to northea st current occurs wi t h the northwest wi nds wh i ch confi rms t h i s observa t i on .

Large defl ecti on angl es were a l so observed i n the i nterva l 24 to 25 August when wi nds were southeasterly

32

and the beacons moved the the northeast . There i s n o apparent expl anati on of thi s dri ft but i t d i d c on­t i nue dur i ng 25 to 28 August i n the same general d i recti on. Th i s may have been the res u l t of the normal wi nd-generated water current added to the Macken z i e Ri ver d i scharge current through the Mi dd l e and West Channel s .

Beacon #8 s howed a remarkab l e defl ecti on ang l e of 84° to the l eft of the wi nd for wh i ch there i s no a pparent expl a nat i on, where the dr i ft was s outh­westward w i th s outheaster ly wi nds .

A f i na l grou p of beacons wa s moni tored duri ng September , except for beacon #19 near l 33°W wh i c h moved t owards the s outheast s l owly des pi te fresh b ut decrea s i ng s outheast ·w i nds . The preva i l i ng wi nd s pri or to th i s date had been moderate s outh­ea sterl y or merel y l i ght var i abl e .

Tab l e I I I l i sts the med i an a nd average dri ft rates and defl ect i on ang l es for each beacon by data and area . For the fi rst four beacons for whi ch there were twe l v e to fi fteen days of dr i ft data avai l abl e , med i a n val ues of the rates a nd ang l es were used to

. reduce the effect of extreme val ues on t h e ca l cu l a ­t i ons . Later , beacons were only tracked bri efly a nd a n arbi trary deci s i on was made to u se med i a ns when fi ve or more d r i ft i nterva l s were avai l abl e , and averages for fewer dri ft i nterva l s .

I f the dr i ft rat i os and d efl ect i on angl es are aver­aged on a month ly bas i s i gnor i ng l ocat i on , the defl ect i on ang l es are 14° to the l eft of the wi nd i n J u l y , 2 2 ° to the r i ght i n August and 15° to the l eft i n September . The rati o of the i ce dr i ft s peed t o wi nds peed i ncreases from 0 . 0074 i n J u l y to 0 . 0163 i n August a nd to 0 . 0253 i n September .

Tabl e IV s hows one further analys i s of the beacon dr i ft data . A compar i s on was made of the Is potl wi nds reported when the beacons were set out w ith those deri ved from the mean d a i l y pressure c harts . I t i s recogni zed that t h i s procedure c ompares a s pot report to a t ime average but neverthel ess s ome use­ful res u l ts can be obtai ned . I n cases where the dr i ft i nterval wa s more than one day , only a s i ng l e c hart was used i n deri v i ng the wi nd because the s pot report was for the beg i nni ng of the dr i ft peri od onl y . For comput i ng the dr i ft defl ect i on a ngl e a nd speed rati os , average wi nd s over the two or t hree days of dr i ft were u sed .

TABL E I I I

I C E BEACON DRI FT RATES AND ANGULAR DEFLECTIONS

Near 137 °W: Near 135°W : Near 133°W : Defl ect i on Speed Defl ect i on Speed Defl ect i on Speed

Ang l e* Rat i o Ang l e* Rat i o Ang l e* Rat i o Vi Vi Vi VW VW V;;

# 1 July _ 5° 0. 0067 # 2 July _ 2° 0. 0096 # 3 July - 10 0. 0067 # 4 July - 37 0. 0067 # 4A August _ 6 ° 0. 0081 # 5 August +55 0. 0181 w # 6 August +60 0. 0208 w # 8 August - 19 0. 0183 #12 Sept . - 20 0. 0141 #13 Sept . - 12 0. 0318 #14 Sept . - 11 0. 0343 #16 Sept . - 3 0 . 0337 #17 Sept . - 16 0. 0152 #18 Sept . - 1 0. 0292 #19 Sept . -76 0. 0065 #31 Sept . +15 0. 0244 #32 Sept . - 14 0. 0381

HEANS - 8 0. 0256 +53 0. 0202 -23 0 . 0126 HEDIANS - 11 0. 0281 - 16 0. 0096

* Pos i t i ve ang l es are to t he ri g ht of the w i nd .

TABLE IV

REPORTED WI NDS COMPARED W ITH DERIVED W I NDS

Date Observed Wi nds Vo Deri ved W i nd s Vd Angu l ar Speed

D i rect i on Speed D i rect i on Speed D i fference Rat i o

Degrees Knots Degrees Knots Degrees Vo Vd

July 15-16 0600 10 1000 12 +40 0 .83 16-17 155 7 145 10 - 10 0. 7 0 17-18 180 6 210 9 +30 0. 67 18- 19 145 7 055 6 - 90 1 . 17 19- 20 290 11 340 12 +50 0. 92 2 0- 21 325 10 325 10 0 1. 00 21-22 080 9 ( L i g ht and vari abl e ) 22- 24 065 13 090 20 +25 0. 65 w -J::> 28-29 180 7 215 11 +35 0. 64 30-31 175 3 125 9 - 50 0. 33

Aug . 01- 02 315 9 315 12 0 0 . 7 5 02- 03 355 4 ( Li ght and vari abl e ) 20-21 030 5 055 12 +25 0. 42 23- 24 135 10 130 '10 0 0. 67 24- 25 155 10 130 15 - 2 5 0. 67 25- 28 165 10 130 12 -35 0 .83

Sept . 06- 07 07 0 5 ( L i g ht and vari abl e ) 07- 09 050 5 125 6 +75 0 . 83 09- 10 145 13 140 12 - 5 1. 08 09- 10 135 12 140 12 + 5 1. 00 10- 11 185 10 ( L i g ht and vari abl e ) 11-13 090 20 125 2 0 +35 1. 00 11-13 095 17 125 2 0 - 30 0 . 8 5

MEDIAN + 5 0. 83

35

The med i a n val ues at t he end of the tabl e are not parti cu l ar ly s i gn i fi cant because ; n practica l fore­casti ng , the anal yst wi l l be wor k i ng w i th both deri ved and reported w i nd s on a rea l -t ime ba s i s and wi l l pred i ct the i ce moti o n on the ba s i s of forecast obta i ned from the prognost i c weather c hart . I t i s perti nent to note , however , that the abnorma l cases i n th i s tabl e are associ ated wi th the same deve l op­i ng s torm i n the J u ly 18 to 20 peri od noted i n para . 5 . 2 . 3 . 2 . I n genera l , a bnorma l rat io s are a s soc i a ted wi th l i ghter wi nds - a rather unfortunate c i rcumstance i n actual practi ce .

5 . 3 Pred i ct i on of the Gross Features of the Summer Retreat of the Pol ar Pack i n the Beaufort Sea

5 . 3 . 1 I n troduct i on

Early knowl edge of whether the s ummer o perat i ng sea son ; n the southern Beaufort Sea i s go i ng to deve l op as a ' good ' or ' bad ' i ce year wou l d be of great val ue to compan i es conducti ng off­s hore expl orat ion or mari ne tran sportati on i n the area . Wi th th i s i n m i nd , an exami nati on of about twenty years of i ce and meteoro l og i ca l record s was undertaken i n an a ttempt to deter­mi ne factors rel ated to pred i cti on .

5 . 3 . 2 Method

As a s tarti ng po i nt , the l ocat i on of the i ce edge between Ban ks I s l a nd and Po i nt Barrow , Al a s ka , was pl otted for m i d­J ul y , earl y and l ate August and l ate September for each year between 1955 and 1974 . F i gures 16 , 17 and 18 are exampl es . An arbi trary assessment was made by c l a ss i fy i ng each of these twenty years as good , bad or fa i r on the bas i s of the t im i ng and extent of the c l eari ng . Havi ng made th i s i n i ti a l separa­t i on , the meteorol og i ca l cond i t ions i n the Arct i c Bas i n wh i c h contri bu ted to these good and bad years were exami ned .

The normal atmospheric pressure pattern i n the Arct i c Bas i n i s anti - cycl o n i c wi th one semi - permanent l ow press ure area centered near the Al eut i a n I s l ands and a nother over the waters around I cel and . Both these centres vary i n i ntens i ty and general l ocati on from year to year a s wel l a s from month to month . F i gure 19 i s a general geograph i c reference c hart of the Arcti c Bas i n s howi ng a l so the major i ce dri ft pattern .

Duri ng the a utumn and earl y wi nter , a h i gh pres sure centre bu i l ds up i n northeastern S i ber i a and a fl a t centre of h i gh north of the Chuckc h i Sea i s transformed by November i nto a s trong ri dge extend i ng from the New S i beri an I s l ands across the northern Chuc kch i Sea towards Amundsen Gul f and the Macken z i e Val l ey ( F i gure 20a ) . At th i s s eason , northwe st wi nds are preval ent a l ong the Arcti c coas t a n d the norma l moti on of the pac k i s onshore . By m i d-wi nter , a separate

36

h i gh devel ops over the Arcti c Ocean (F i g ure 20b ) . Thi s centre s l owly dr i fts towards Green l and as s pr i ng approaches (F i g ure 20c ) . Mean wi nds i n the Beaufort Sea duri ng th i s peri od , f i rst decrease to l i g ht, then veer s l owl y towards the south­east a s the h i gh becomes establ i s hed i n the El l esmere-Greenl and secti on i n Apri l and May . The resu l t i ng s outheast wi nds on the north coast of Al a s ka , i n the Mac kenz i e Va l l ey and i n the Beaufort Sea res u l t i n the formati on of an extens i ve pol ynya i n the Cape Bathurst- Cape Kel l ett area i n a norma l season .

Over the rema i nder of the Arcti c Bas i n , a cycl on i c c i rcu l ati on i s preval ent and the Icel and i c l ow may extend i ts i nfl uence northea stward to Spi tzbergen and Novaya Zeml ya . I n s ome years i t even affects the east Greenl a nd coast and the area extend­i ng acros s the pol e i nto the North Ameri can sector of the Arcti c Ocea n .

.

I n so cal l ed I badl years , th i s l atter c i rcu l ati on i s common whi l e i n I goodl i ce years , h i gh pres sure i s domi nant i n the areas of the Queen El i zabeth I s l ands and northern Greenl and .

The maj or press ure pattern i s refl ected i n t he i ce movement and it ha s been known s i nce the days of Nansen that there i s a pers i stent fl ux of i ce from the area of the Laptev Sea and the New S i beri an I s l ands , across the pol e and i nto the a rea north of Greenl and . Most of th i s i c e cont i nues s outhward d own the east Greenl and coast but a porti on may rema i n wi th i n the Bas i n a s a const i tuent of the North Ameri can Gyre . Thi s i ce mass i f , centred n orth of Ber i ng Stra i t, rotates i n a c l ock-wi se d i recti on on the North Ameri can s i de of the Trans­P ol ar dri ft stream (F i gure 1 9 ) .

The i ce wi th i n the Trans-Pol ar Dri ft Stream i s made u p of a h i g h proporti on of fi rst year fl oes a s i t l eaves the S i beri an coast but the rate of mot i on and the degree of mel ti ng i s such that ma i nl y mUl t i -year fl oes are present when the i c e reaches Greenl and waters . W i th i n the North Ameri can Gyre, mUl ti -year i ce i s c l earl y preval ent except i n the Beaufort and C huckchi Seas where mel ti ng i s more s i gn i f i cant and a n offshore component to the dri ft i s common .

W i th i n the context of these maj or i ce dri ft features i t i s apparent that a southward fl ux of i ce acros s the l i ne from Barter I sl and to Mou l d Bay (l i ne A-A on F i gures 20a, b a nd c ) wi l l i ncrease the amount of second-year and mul t i -year i ce i n the s outhern Beaufort Sea and i ncrease the vol ume of i ce that must be mel ted before c l eari ng devel ops s i nce these i ce types are thi c ker than f irst-year i c e .

U s i ng the coord i nates BOoN l BOoW a s a n eas i l y i dent i f i ed poi n t wi th i n the North American Gyre , i t i s cl ear that a fl ux s outh­ward across the l i ne Boo N l BOoW to El l esmere I l and (l i ne C-D i n F i gures 20a , b and c) w i l l i ncrea se t he v ol ume of i ce i n

L / '-'--->--

j LEGEN D

.y.,� Locati on of I ce E dge / mi d J u ly early Augus t - - - - ­

l ate Augus t - - - . -. -1 ate September

I -� -I I ! � >�v-�_/

l ( \

F igure 16 . 1968 , a Igo od l i ce year .

The area th at was open water th roughout i s s ti pl ed

I f

- . ���\ . . . r--.... \ "----

�,�� COI';>C! \

< � --..... '­-.., L' Al though the Cape Bath urst polynya vias poorly deve l oped i n t·1ay and June , the i ce

_re treated rapi dl�

_� n J u l! and easy acces s around Poi nt Barrow \'las poss i b l e by Ju ly 20. / ) \ � I

w -....j

Locat ion of Ice Edge : m i d-Ju l y

LEGEND

ear ly August - - - - -l ate August - · - . _ .

1 ate September }( 'I. )( X x: X

Fi gure 17 . 1970 , a ' fa i r ' i ce year .

The area that was open water throughout i s st i p l ed .

.. � .

"" / , � Even though the pol ar pack was far from s hore i n the s pri ng months , ons hore w i n ds were

freq uent unt i l mi d J u ly and the po lynya i n the southern Beaufort Sea was s l ow i n deve l op i ng . I Ons hore wi nds and an early freeze up advanced the end of the seas on .

�

___ .. ____ ___ _ _ _ _ . _____ __________ c1

w co

r--------t------------,,"'>-----.----t--- .------..0:---.... ,._.. ) ;< 'f , ><

j I I i

j '

LEGEND / � Location of Ice Edge :

� m i d-Ju l y The area that � early August - - - - - was open water "'f..... 1 ate August - - - . - ' throughout i s / l ate September x x )<. x ){ )( s t i p 1 ed .

! / i / lb · 'f.. lJa,.. /".t I . '0", . � .

/ ' � . / +

! / '} I

/ j ' / . . / /

. I

. t' I . . . . + . . t ·

1 �L._.. r � ->.>\.-<_.----"

I !

// ( F i gure 1 8 .

aarter� I 1701 j;; L:.!l""'. 1 .... � ISland '\ I _ . . b ./

I LATE S EPT 1 974 , a ' poor ' i ce yea r . .-'�

Onshore w i nds and res ul ti ng l ow temperatures pers i s ted th rough mos t of the s ummer res u l ti ng i n one of the wors t i ce years on record .

.�\ ..\- . �c('� "

� �-,-----.. - ------------ -..•.. --

W \.0

.,0

� ,, : -.

�' '" � �= .

�6� x

F i g ure 1 9. GEOGRAPH I CAL RE FEREN CE �1AP.

/ /

! I \ \ / I

� j ;

GREENLAND

�-f-

, i �-J/$

;. 1

+:> o

41

Fi g ure 20a . Mean Sea Leve l Atmospheri c Pres s ure Ch art for November.

A ri dge from a growi ng h i gh p res s ure area i n S i b eri a i s s treng th ­en i ng i ts i nfl uence i n the Ch uckch i and Beaufort Seas . Ons hore wi n ds are common i f the ri dge l i ne dri fts even s l i g ht ly westward . The f l ux l i nes referred to i n the te xt are s h own .

42

F i gure 20b. �lean Sea Level Atmos phe ri c Pres s ure Chart for February .

P res s ures have conti nue d to r i s e and th e ri dge from S i beri a to the Mackenzi e Val l ey i s domi nant . W i nds i n the southern Beaufort Sea are l i ght because of the ri dge l i ne .

43 ---_. __ . __ ._-_._-----

Fi g ure 20 c. Mean Sea Le vel Atmosp heri c P res s ure Chart for �1ay.

The h i gh ove r the Ch uckch i Sea i n February has moved eas tward and comb i nes wi th the trough deve l opi ng i n Central Al as ka to gi ve southeast wi nds i n the Beaufo rt Sea . Polynya and l ead formati on s eaward of the fas t i ce fol l ows q ui ckly .

44

the approaches to t he Beaufort Sea . A fl ux westward across the l i ne to Poi nt Barrow ( l i ne B-C i n F i g ures iOa , b and c ) wou l d decrease i t . Al so a strong northward fl ux across the l i ne from 800 N 1 800W to Cape Chel yu s k i n ( C - E i n Fi gure 20a , b and c ) woul d a l so tend to i ncrea se the vol ume i n the s ame way .

I n order to deri ve a quanti tati ve measure of these fl uxes , s ea l evel pressure d i fferences i n mi l l i bars were obtai ned by s ubtract i ng the press ure at the second l ocati o n from that at the f irst at the fo l l owi ng pa i rs of l ocati ons ( s hown i n F i gure 20a ) : Barter I s l and and Moul d Bay , Pt . Barrow and 800 N l 80oW , 800N l 80 0 E and 85°N 900W and 800 N and 1 800W and Cape Chel yus k i n . The press ure d i fferences between l ocati ons 800 N l 800W and Cape Che lyu s ki n were arbi trari l y reduced by 50% because of the i r remotenes s.. I t cou l d be argued that the fl ux resu l t i ng from press ure d i fferences between these two po i nts wou l d have l i ttl e d i rect i nfl uence i n the same year on i ce vol umes i n the Beaufort Sea except perhaps by the transmi s s i on of i nterna l stres s . These pres s ure d i fferences were obta i ned from t he mean month ly atmospher i c charts for January , February and March of the year of concern . The wei ghted d i fferences between pa i rs of l ocati ons and for these t hree months were t hen tota l l ed to produce a fl ux i ndex .

Some of the termi nati on po i nts of these l i nes were c hosen accord i ng to the avai l ab i l i ty of atmos pher ic pres s ure data i ns tead of on the bas i s of the overa l l i ce dr i ft pattern . The po i nt 800N 1 800W i s an exampl e s i nce a l ocat i o n somewhat further to the ea st woul d more nearl y represent the centre of the North Ameri can Gyre .

5 . 3 . 3 Res u l ts

The fi nal resu l ts of these ca l cul at ions are s hown in Tabl e V and are s ummari zed a s fo l l ows :

i n 9 of the 1 0 good years , the i ndex ( pres s ure d i fference total ) fel l between - 2 0 and 1 9 .

i n 4 fa i r years the i ndex was - 1 6 , - 2 3 , 28 and 30 .

i n 5 poor years the i ndex fel l between 22 and 40 .

I f 20 i s ta ken a s t he upper l imi t of the i ndex i n a good year , 20 to 25 a s an i nd i ca t i on of a fa i r year and over 25 as a s i gn of a poor year then :

9 of the 1 0 good years wou l d have been s uccessfu l l y pre­d i cted and 2 of the fa i r years wou l d have been forecast as good .

--

the 4 fa i r years are not pred i cted correctly , the two men­t i oned above bei na ca l l ed good , a nd the other two poor . ¥ --

5 of the 6 poor years are correctly forecast and the other wou l d have been forecast as fai r .

4 5

Thus 1 4 seasons wou l d have been correctl y pred i c ted ; three wou l d be one category wo )�se than expected , three wou l d be better than forecast , two of them be ing one better and the th i rd , two better .

The rea son t he i ndex i s so vari a bl e i n a fa i r year i s not ev i ­dent and no rea son for i t has been i denti fi ed . El imi nat i on of some of the fl uxes , i nc l u s i on of December and/ or Apri l fi gures were a l l tested and no s i gn i fi cant improvement was noted . No cl ar i fi ca t i on was found i n a study of the pos i t i on or i ntens i ty of the Al eut i an Low . Cl oser correl at ion wi th t he pos i t i o n and i ntens i ty of the I cel and i c Low seems unl i kel y because of i ts remoteness and t h i s i s a l ready taken i nto account , i n part , by the atmospher i c pres s ure at Cape Chel yus k i n and the l a st of the fl ux l i nes descri bed above .

What i s b e i ng done i s to estimate the mot i o n of the Arct i c Pac k accord i ng to earl y wi nter atmospheri c press ure patterns and then to a s s ume that the effect wi l l pers i s t . Major c hanges i n the pres s ure pattern reg ime do occur between t he fi rst three months of the year and the brea k- up season and these are respon s i b l e for the fa i l ure years . As mi g ht be expected , l ong-range forecast i ng i mperfectl y pred i cts the nature of the i ce year but neverthel ess may be of some u se . Years l i ke 1 97 2 wh i c h are anomol ous i n many res pects rare l y f i t patterns devel oped i n th i s manner . I t remai ns on ly to i dent i fy the rea sons for such anoma l i es so that i ncorrect pred i ct i ons can be avo i d ed .

TABL E V

General I ce Cond i t i ons - Beaufort Sea

Year Ice Year Total I ce F l u x I ndex C l a s s i f i c at i on January , February , March

1 95 5 Fa i r - 1 6 1 956 Poor 35 1 957 Poor 22 1 958 Good 6 1 959 Poor 37 1 960 Good - 1 1 1 961 Good 1 9 1 962 Good 3 1 963 Good 1 4 1 964 Poor 40 1 965 Fa i r 30 1 966 Good - 2 1 1 967 Poor 26 1 968 Good 1 96 9 Fa i r - 23 1 970 Good 1 5 1 97 1 Good 8 1 972 Good 54 1 97 3 Fa i r 28 1 974 Poor 29

46

5 . 4 A Study of Fl oe S i ze i n the Beaufort Sea

5 . 4 . 1 I n troduction

Shoul d exp l oratory dri l l i ng from dri l l s h i p s be attempted i n t he coastal zone o f the Beaufort Sea , i t i s a pparent tha t some knowl edge of l i kel y fl oe s i zes i s necessary i f an a s ses sment i s to be made of the ha zard that cou l d be created by occa­s i onal encroach i ng fl oes . Duri ng the per i od s of h i g h i ce con­centrat ions i t i s a s s umed that dri l l s h i p s wou l d depart .

5 . 4 . 2 Ava i l a bl e Data

At present both i ce reconna i s sance a i rcraft of the Atmospheri c Envi ronment Serv i ce carry 70 mm V i nten cameras i n a trimetra­gon array wh i ch covers t he area bel ow t he a i rcraft and to each s i de at a 62° angl e . I n 1 974 , the ori entati on of t he obl i que cameras was such that a narrow s tri p was omi tted between the verti ca l and ob l i que fi el d s of v i ew but th i s probl em ha s s i nce been el imi nated . Except for th i s narrow str i p , the camera array covered the a rea bel ow the a i rcraft and to the s i des i n a swath that was 3 . 26 times the a i rcraft ' s a l t i tude . I n l ate August , 1 974 a spec i a l p hotograph i c m i s s i o n wa s fl own dur i ng nearly perfect weather cond i t ions and prov i ded a tota l of 5 , 200 photographs from an a l t i tude of about 1 ,850 metres resu l ti ng i n l a tera l coverage of 6 km a l ong a 2 ,470 km fl i ght track . The sad part of the mi s s i on was that 7 0% of i t was fl own over i ce concentrati ons greater than seven tenths w i th the resu l t that onl y the data from the edges of the pac k was u seful . Thi s report concerns those areas near the edge of the pack and s peci f i ca l l y dea l s with the port i o ns shown i n Fi gure 21 . An exampl e of the imagery on l eg C i s presented i n F i gure 22 .

The weekl y h i s tori cal i ce c harts referred to i n Sect ion 4 . 1 portray the amount , type and l ocat ion of the i ce pac k i n the Beaufort Sea and a l so a l imi ted i nd i cati on of the s i zes of fl oes encountered . As part of the s tudy conducted by F ENCO , the proport ion of fl oes greater than 1 00 metres i n s i ze were recorded and anal yzed . For the years 1 966 to 1 973 t h i s data appears on the i ce c harts d i rectly a l though s i ze reporti ng i s not a l ways a s compl etel y s pec i fi ed a s i s the concentrati o n and age of the i ce . Part of the rea son for th i s i s the use of sate l l i te imagery wh i c h does not permi t th i s refi nement . For the years 1 953 to 1 965 the data i s aga i n on ly parti a l l y com­p l ete where the s i ze i nterval reported i n tho se years was : up to 1 0 metres , 1 0 to 1 ,000 metres and over 1 , 000 metres . Arbi trari l y , the tenths of i ce i n the m i dd l e category were ha l ved to represent the proportions greater and l es s than 1 00 metres . These two data sets were the i nput to the FENCO ana l ys i s .

ds bel oj I a1 rcraft

-- .. cr.., .. I fQ$!lt Cl!ll:P

L ijmi t of lV i s i b i l

, - -

r- "1 i te

� �� 5 tenth s F Y 0�P �

Open Water ,. 6�

Fy - Fi rs t Year I ce

- 8 ten ths Fi rs t Year

I ce

Fi g ure 2 1 . Photograph i c I ce Reconnai s s a nce Mi s s i on of 2 7 Augus t 1 9 74 s howi ng track of ai rcraft , i ce con­

centrat ions and l ocati on of l eg s A to E wh i ch were analyzed for fl oe s i zes . Fl i g ht a l t i tude was 1 850 ffi .

+::> -....J

' Fi gure 22 . S ampl e frames from the r i ght and centre c ameras on l eg E . The s i ze of the gap between the c amera s tri ps can be est imated from the l arge fl oe on the l ower r i ght wh i c h appears i n four frames . The amount of overl ap from frame to frame i s al s o evi dent but th i s v ari es from l eg to l eg because of the w i nd effect on ai r s peed .

� co

49

5 . 4 . 3 Ana l ys i s

Leg A B C 0 1 02 E

Leg A B C 01 02 E

Contact pri nts deri ved from the Augu st p hoto mi s s i on were stud i ed at l ength and a l t hough the l eft s i de imagery was par­t i a l l y obscured by fogged f i l m ( before or after expos ure but not dur i ng the mi s s i o n ) i t was poss i bl e to extract con s i dera­bl e data . From the bas i c s pec i f i cat i ons concerni ng camera angl es . f i el d s of v i ew and a l t i tude of the a i rcraft , i t was poss i bl e to q uant i fy the area appeari ng i n both vert i cal and obl i que frames and thus to est imate qu i te accuratel y the l ength ( s i ze ) of a l l the fl oes appear i ng i n the imagery . The fol l ow i ng ; s a s ummary of th i s ana lys i s .

NUMBER OF FLOES OF VARI OUS S I ZES - 27 August 1 974

Over 500 to 1 00 to Under Number of Ice Conce n . 1 000 m 1 000 m 500 m 1 00 m Frames

7 6 6 5 1 805 1 37 20 7 24 3 tenths 1 3 38 1 200 6540 1 40 6 25 64 1 740 2300 60 6 6 6 1 800 1 37 20 1 1 3 2

57 93 2845 4770 1 23 9+ 36 26 1 90 2 1 60 1 07 2

I nd i v i dual fl oes i n numbers a pproach i ng one hundred i n a s i n­g l e frame cou l d not be accurately counted . I ns tead , t hree des i g nators , ( pl enti ful , many , and very many ) were a s s i gned when counti ng became d i ffi cu l t a nd arbi trary numbers 2 5 , 50 and 67 were a s s i gned to these . These were used i n summations and a s a resu l t , data col umns 3 a nd 4 a bove are on ly approx i ­mate . Neverthel ess , the preponderance of sma l l fl oes and i ce ca kes i s ev i dent .

The next step was to exami ne the number of fl oes rel at i ve to the over 1 000 m fl oe s i ze . For i ns tance , on l eg B , t here were 38 fl oes i n t he 500 to 1 , 000 m s i ze range wh i l e 1 3 fl oes of the over 1 , 000 m s i ze were counted : a 1 : 3 rati o . The rel a­t i ve fl oe s i zes on each of the l egs were rounded off a s fol l ows :

Over 500 to 1 00 to Under Total Ice Tenths l arger 1 000 m 1 000 m 500 m 1 00 m Concen . Fl oes ( Reported )

1 1 2 5 1 80 3 1 1 3 90 500 6 2 1 2 7 0 90 6 2 1 1 300 2300 2 1 1 2 45 80 9 5 1 1 5 60 2 1

Referri ng to t he fl oe s i ze ranges a bove , one can s ay t hat on Leg A t here were 27 fl oes greater than 1 00 m i n l ength ( 1 +1 +25) for every 1 80 sma l l er fl oes , a rat i o of about 1 : 7 .

6. D I SCUSS I ON

50

S imi l arl y , on Leg B there were 94 fl oes l arger than 1 00 m for each 500 smal l er ones , a rat i o of 1 : 5 . On Leg C the rat i o i s near ly even : on 01 it i s 1 : 7 ; on 02 i t i s 1 : 2 and on Leg E i t i s 1 : 8 . I t i s s i gn i fi cant that the rati o i s l owest on Leg 02 where the i ce concentrati on wa s h i ghest .

The fl oe s i ze ana l ys i s conducted by FENCO i s s ummari zed i n F i gures 1 8 to 23 for t he same areas u sed i n t he i ce concentra­t i on study ( Fi gure 1 ) . I n the spri ng the l arger fl oe s i zes i n a l l areas are to be expected and po i nts out that any effort to extend the sea son of operati on s hou l d be concentrated i n the a utumn when the i ce i s t h i n and the fl oes present are genera l ly wea ker than i n the s pri ng and the early s ummer .

To get a better apprec i at i on of the factors i nfl uenc i ng floe s i zes one must con s i der the proces ses at wor k on the i ce . Duri ng the wi nter , the sha l l ow coas ta l waters are covered wi t h a str i p of fas t i ce - i n effect a s i ng l e fl oe of immense d imens i on . I t i s u s ua l l y made up of a mul ti tude of i ce ca kes and sma l l fl oes wh i ch were broken by waves after t hei r i n i ­ti a l formati on early i n the autumn ; were l ater pus hed together by ons hore wi nds and were then cemented together by subsequent freezi ng wh i c h a l s o i ncreased t hei r thi c knes s . As a conse­quence t he fa st i ce u sua l l y has a number of " seams " wi t h i n i t wh i c h w i l l have a tendency , o n s u bsequent break-up to produce fl oes i n the "smal l fl oe I I or l ow s i ze range . It s eems there­fore , that t he decay of i ce from fas t i ce down to sma l l fl oes and i ce ca kes wi l l rel ate to condi ti ons duri ng freeze-u p and to t hose d uri ng brea k-up . I n t he a utumn , meteoro l og ica l con­d i t i ons wi l l determ ine the spaci ng of the seams but at brea k-up , geograph i c l ocation wi l l a l so d i ctate that partia l l y protected areas wi l l produce young fl oes that are l arger than those i n exposed areas . S imi l a rl y , mechan ica l fractur­i ng by wave acti on wi l l depend on the extent and confi g uration o f ear ly po lynyas , to wi nd d i recti on a nd to w i nd s trength once a pol ynya i s formed .

6 . 1 I ce C l ima to l ogy

The ana l ys i s reported i n Section 5 . 1 i s rel ated to condi ti ons between mi d-May and l ate October a nd is g i ven in s ome detai l for th i s port i o n of the year wh i ch i ncl udes the open water period . Very l i ttl e actual data for the darker months i s avai l ab l e but i n recent years i nfrared satel l i te imagery has begun to fi l l t h i s gap . On the bas i s of t h i s l im i ted amount o f i nformati o n , the fol l owi ng cond i ti on s are thought to occur d ur i ng the darker month s .

(a ) Duri ng November and December the fa st i ce grows steadi l y i n th i c knes s but i t a l so expan�s i n w idth i n a s eri es of s teps t hat are rel a ted to per i ods of onshore wi nds . F l oes are consol i dated onto the prev i ou s fast i ce edge wh i c h then rema i ns fi xed i n p l ace duri ng s u bsequent offs hore dri fts . Thi s i s vari ab l e from one year to another

51

----+ �--�----���----���--------�--------�--�----�� 80 ;e

!!....

- - ----- ---- -+---------+

w U Z w � �

�--_+�r.�-�--------_+--------�--------_+--���_+� 60 � - - -. - -------- _.--. I�--ft-_ � 400 0

- - - . - ---- ------t___------------+-------r-----� ----�-

U U o u.. o

r----+�--��-+·-------+---------+---------+-------r-+� 40 r . . ---.-� --t___-----1_

- - . = 0

/ --- � - . . --� - -I ._- --+ - _ .. + . _ - - "-

.. • �- _ ., _ _ � ___ -4.- .___ _____ i _ _

U Z w � C w

�---+��---�---------+---------4---------+--------�� 20 �

I _ _. • _ . _

FI GURE 2 3 . FREQUEN CY O F OCCURREN CE OF FLOES : ME DI UM S I ZE O R GREATER ( O VE R 1 00 �'1E TRES ) ARE/I. 1 ( F i g ure 1 ) .

5 0

The ve ry dramati c decreas e i n fl oe s i ze i n Mackenzi e B ay i n June i s al so a ccompani ed by a s i mi l a r change i n the total i ce con­

cen trati on . The remn an t proporti on of l a rge fl oes duri n g August and September occur d uri n g " poo r" seasons when p l enti fu l i ce i s p res e nt

o r when coas tal i ntrus i ons devel op from the wes t of Hers che l I s l and .

52

- - - ".'---- J7>-.c------f-----+-+---\---t=ri 8 0 � /' i >/ • . ! UJ U Z UJ ac ac ---\---\-+--; 6 0 :::> U U o u.. o

�/I -/ •. -_ . : . - - · --·----1 �0- -- '20

0

Ou...� - _ --fL - - I ---··-r-�-l --.----t-� �= / i I I I ' I ! 'I i : , I ! 1 4 ,1 ;' ( . . l 1 1 ; ;" : S L 9 16 :)J :) .) 'i 1 3 ,0 2 7 3 10 i1 7. 11 I 1: ;.'1' J I..' � J f: J l l LY /\l) (j�JST S ( Yl f i.l b f R

DATE fl \S 71 'L9 5 0 O C T'J \? t R

F I GURE 24 . FREQUEN CY OF OCCURRE N CE OF FLOES : ME DI UM S I Z E OR GREATE R ( OVE R 1 00 METRE S ) AREA 2 ( Fi gure 1 ) .

A decreas e i n fl oe s i ze i s rap i d i n t h e fas t i ce z one and a

very rap i d decreas e i n the amoun t of i ce a l s o occurs . The comp l ete abs e nce of l arger fl oes i n e ar ly September i s thoug ht to be re l ated

to wave acti on , and to the fact that th i s is the e as tern coastal zon e wh i ch i s mos t d i ffi cu l t for e ncroach i ng i ce to rea ch .

.. . . . . _-

� 80 0t(] , ���---. -r-- .( .. - _ . ·· 1 � .10 %

53

80 � u.J U Z u.J Or:!: ex E t _+_: · 1-- .. 1 . . .. . . . . . . .

---\---\1---1 60 ::>

,-- I- - . " - . -Eri--. ---:V-

8 .- �

u u o U-o

4 0 >-­U Z u.J ::> o u.J �,:JC----- --+----�--. -�A ----.-}-------+l-I 2 0 �

�!���������������������� l d 2 1 28 4 1 1 1 8 o 8 15 22 29 5 M AY J U N E OCTO B E R

FI GURE 2 5 . FREQUEN CY OF OCCURRENCE O F FLOES : ME DI UM S I Z E OR

GREATE R ( OVE R 1 00 METRES ) ji,REJ\ 3 ( Fi g u re 1 ) .

I n th e Amunds e n Gu l f area , the propo rti on of l a rger fl oes

i s -I owet� i n the s pri ng becaus e of th e conti n ua 1 moti on of the offs hore

pack and beca us e of the form�t; on of l eads and po lynyas . The decreas e i n n umbe rs of l a rger fl oes duri n g the s umme r i s much

s l owe r th a n i n the coas tal areas .

54

UJ U Z UJ a:: ------�--+_�r�� 60 �

--�----- ----+-----;-�� 40

U U o u... o >­U Z w ::J (3 w

-------1------�� 20 �

! ! I 1 I ! 9 16 23 J) 6 1 3 i r) 2 7 3 10 1 / L tl I

J U U A U ':; U:'T S ( P T E II\ B E R DATE

FI GURE 26 . FREQUE N CY O F OCCURRENCE O F FLOES : ME D I UM S I ZE OR

GREATE R ( OVE R 1 00 METRES ) AREA 4 ( F i gure 1 ) . I n th i s i n termedi ate area the rate of decrease i n f l oe

s i ze i s very much reduced because the i ce concentrat ion i tsel f remai ns cons i derab ly h i gh er. The n umber of l arge r fl oes i s

s i gni fi cantl y greater , p a rti cu l arly i n Aug us t .

55

"'"

1E 80% \

FI GURE 27 . FREQUENCY OF OCCURREN CE O F FLOES : ME DI UM S I Z E OR GREATE R ( OVER 1 00 METRE S ) AREA 5 ( Fi gure 1 ) .

100

80 o-e LJ.J U Z LJ.J ac c.:: 60 :J U U 0 lL 0

4 0 >-U Z w :J 0 UJ

20 �

o

The p roport i on of l a rge r fl oes i s a lways s i gn i fi cant i n

th i s offs hore a rea and at the s ame t ime on ly p a rti al di s p e rs al of

th e i ce can be e�pected.

56

�--------1----------+---------�------�� 80 � o , w U Z W 0::: a:: ·�-------4--------�---------r---------� 6 0 �

:..0-_-+- - _

----r-----·---4------�=+--------� 4 0

U U o u.. o >­U Z w ::::l o w I----I-�+-. --1--+----1 -

20 �

! i 1

9 16 23 30 6 1 3 20 27 J U LY A U G � ST

DATE

FI GURE 28 . FREQUENCY OF OCCURRENCE OF FLOES ME DI UM S I ZE OR GREATER (OVE R 1 00 METRES ) AREA 6 ( Fi gure 1 ) .

o 5

I n the northern offshore area a s i gni fi cant n umber of

l arger fl oes are a lways pres en t and conge sted i ce condi ti ons are

norma l .

57

but the u l t i mate extent of the fast i ce i s rel ated to water depth . The 20 metre i sobath normal l y defi nes the offs hore l i mi ts of the fa st i ce and th i s extent i s t hought to be atta i ned i n Februa ry or March . There i s probab ly a s l i g ht rel at i on s h i o between the nverage fa s t i ce th i ckness and the l ocat i o n of t he s eaward edge but the vari at i on i s not great . Es sent i a l l y t he keel depth of s i g n i fi cant ri dges i s expected to be part i a l l y rel ated to i ce t h i c kness and s u bsequent ground i ng of the keel s i nfl uences the l ocat ion of the fas t i ce edge .

( b ) The fa st i ce can extend wel l beyond i ts u sua l range of w idth i n those s easons when ons hore wi nds are preva l ent o r the � i spers i ng offs hore wi nd s are weak when they do devel op . 1 974 wa s an exampl e of thi s cond i t i o n . Suc h cases are unstabl e a nd revers i on to the normal extent defi ned by the 20 metre i sobath can q u i c k ly occur . The oppos i te extreme , when the fast i ce i s much narrower t han u s ua l i s much l es s l i ke ly to occur because of t he grounded i ce at the normal edge of t he fast i ce zone .

( c ) Duri ng the wi nter , the offs hore pack rema i n s i n steady mot i o n i n response to mean wi nd cond i t i ons but concentrati ons o f t he t h i c ker i ce are usua l l y e i g ht to ten tenths des p i te the movement . F l aw l eads ca n deve l op but are q u i c kl y covered wi t h new , young i ce wh i ch s u bse­quent ly grows i nto f i r st-year i ce . Depend i ng on t im i ng , there may be exten s i ve areas of fi rst-year i ce cover wh i c h are s ubstanti a l l y t h i nner than i n other area s . The most l i kel y pl a ce to encounter th i s t h i nner pac k i s i n the Cape Bat hurst to Cape Kel l ett area ( See F i gure 1 9 ) .

( d ) The devel opment of fl aw l eads and offs hore pol ynyas most ly o c c u r i n Apr i l when refreez i ng i s s l ower . The i r rel at ion to offs hore wi nd fl ow i s paramount and temperature cons i derat i ons are secondary . F i g ure 20c , t he l ong-term norma l surface pres sure c harts for May , i l l u s trates the norma l devel opment of offshore wi nd s . I n a spec i fi c year , w i nd patterns o f th i s type can vary s i gn i fi cantl y where i n 1 97 5 the d i s persa l devel oped i n March , i n 1 974 i t wa s del ayed u nt i l 1 ate fVlay .

( e ) A pattern of regu l arl y s paced l eads among the mov i ng offs hore pack i s somet imes s een i n satel l i te i magery and has a l so been reported by Apri l i ce reconna i s sance fl i ghts . As yet though , there i s no data regard i ng the i r spac i ng i n rel at i on to i ce type , wi nd s trength or wi nd d i recti on .

( f ) Beca use of preva i l i ng i ce t h i c knes s , mean fl oe s i ze and i ce s trength , the earl y part of the operati ng season wou l d be more ha zardous for dr i l l s h i ps than the m i dd l e and end of t he season . Therefore , any l engthen i ng of the operat i ng season s hou l d be i n the fal l when the i c e i s t h i n and weaker becau se of i ts h i g h s a l i n i ty .

6 . 2 I nd i v i dua l I ce Fl oes

A better knowl edge of the water c urrents i n the s urface waters of the southern Beaufort Sea i s requ i red to more ful l y understand

58

spec ifi c fl oe mot i ons . On the bas i s of rad i o beacon track i ng of fl oes there appears to be a rea l seasonal i ncrease in dri ft-rates rel ati ve to the w i nd s peed wh i ch s houl d be ta ken i nto account i n future i ce forecast i ng i n the area . Dri ft measurements are i n genera l agreement wi th earl i er s tud i es by Zubov ( 1 945 ) , Shu l e i k i n ( 1 953 ) a nd Fukutomi ( 1 958 ) , but the probl ems of u nknown and var i ab l e c urrents rema i n .

6 . 3 Gross Features of the Summer Retreat o f the Pac k

Us i ng the methodol ogy for l ong-range pre� i ct i on descri bed i n Secti on 5 . 3 , the i ndex val ue for the . 1975 i ce season i s 9 , comforta­b ly fi tti ng i nto the ' good ' range . Up �nt i l earl y August , th i s year had devel oped as expected , but i n the l ate s ummer a maj or return of the pack occurred . Further refi nement of th i s forecasti ng procedure may be pos s i bl e by adj ust i ng the centra l po i nt of the pressure i ntercepts so t hat i t more nearly conforms to the centre of the North Amer i ca n Gyre . A further probl em st i l l rema i n s , that of the avai l a­b i l i ty of rel i abl e meteorol ogi cal observat ions from the m i d st of the Arcti c Pac k .

6 . 4 Fl oe S i zes

The percentage of med i um or greater s i zed fl oes wi th i n the Beaufort Sea pack i ce on a week ly ba s i s i s i l l u strated i n Sect i on 5 . 4 .

For practi ca l p urposes , the coastal fast i ce i n the spri ng i s a fl oe of i nfi n i te s i ze . Offs hore , the pac k , mov i ng i n response to wi nd and current , undergoes trans l at iona l and rotat i onal s tres ses but col l i s i ons are not common and waves are a l most non-ex i stent . Compres s i ve forces deform the th i nner i ce muc h more than the t h i c ker fi rst-year or ol d fl oes and hence do not affect fl oe s i ze d i rectl y . The resu l t i s that fl oe s i ze i s great a l though t here i s probab ly some tendency for el ongated fl oes to devel op rather than round or squari s h o nes . These cond i t i ons are evi dent i n LANDSAT i magery i n Apri l and May .

No data i s avai l abl e concerni ng the med i a n fl oe s i ze of the offs hore pack i n May but for argument ' s s a ke , l et us ass i gn 20 km as a s i ze _ estimate . After severa l wee ks , further deformati on w i l l have occurred , the fast i ce may have begun to break u p and i n general , the majori ty of the fl oes wi l l have bro ken at l east once because of i mpacts w i th other fl oes , or because of thermal stress , so that the med i a n s i ze wi l l now be in the 1 0 km range . The number of fl oes wi l l have doub l ed and the number of 20 km fl oes rema i n i ng wi l l have decreased marked l y . I n a nother few weeks the med i a n s i ze may decrease to 1 km . Us i ng th i s argument :

- The average fl oe s i ze of pack i ce decrea ses progres s i vel y dur i ng the s ummer .

- The tota l number o f fl oes i ncrea ses i n earl y s ummer a s the l arge fl oes break up but s ubsequent ly mel t i ng decreases the numbers .

59

- There wi l l be a peri od i n earl y summer when b i g fl oes are predom i nant ; then thei r popu l at ion wi l l decrease stead i l y . Med i um fl oes wi l l predomi nate somewhat l ater than b i g fl oes , then they too wi l l decrea se i n number .

Because of fl oe th i ckness and i ce strength i t i s l i ke ly that the vari ati ons wi th t ime of the popu l ati on of fi rst-year fl oes of a spec i fi c s i ze i s somewhat d i fferent that than for o l d fl oes . Thei r numbers s hou l d peak earl i er and decrease qu i c ker than for stronger o l d i ce . However , the o l d fl oes consti tute l es s than 1 0 percent o f the total pack i n even the worst years i n areas 1 , 2 , 3 and 4 and on ly become s i gn i fi cant i n area 6 ( F i gure 1 ) .

7 . IMP L I CATI ONS AND R ECOMMENDATI ONS

I f ful l deta i l ed i ce forecasts wi th acceptab l e accuracy are to be pro­v i ded , a ful l understand i ng of the annual and seasona l var i at ion of near s urface currents in the southern Beaufort Sea is requ i red .

I t i s recommended that S i de- l ooki ng Ai rborne Radar be provi ded i n AES i ce reconna i s sance a i rcraft as soon a s i t i s practi ca l l y pos s i bl e . A day-by­day knowl edge of the l ocat ion of the edge of the Arcti c i ce pac k wi l l be needed s hou l d dri l l i ng operat ions commence . Reconna i s sance at no more than 48- hour i nterva l s wou l d be ob l i gatory unti l deta i l ed computer i ce pred i ct i on programs are devel oped . These programs coul d i ncl ude the res u l ts of the A I DJ EX proj ect now studyi ng the bas i c p hy s i c s of i ce mot i on . Con­s i deri ng that l ow c l oud and fog obstruct the present aer i a l observat i ons , A i rborne Radar presents a sol ut ion to the pro bl em . There wi l l no doubt be data avai l ab l e from s h i p-based radars a s soon as dri l l i ng p l atforms are i n pos i t i on but i n rough seas these have l im i ted effecti veness . An a i rborne system wi l l be necessary to prov i de the cons i stent coverage requ i red to suppl ement the proposed dri l l i ng p l atform radar observat i ons .

8 . NEEDS FOR FURTHER STUDY

A c l imatol og i ca l study l ooks backward at what i s on record concern i ng prev i ous vari at ions i n envi ronmenta l events . I f the record i s l engthy , many man i pu l at i ons of the data are poss i bl e but i f the record i s s hort , l i tt l e deta i l ed work can be done . There i s a need to di fferenti ate between i ce-free cond i ti ons and open water wi th a few fl oes present i n ongo i ng observat ion programs .

Study of water mot ions i n the upper ten metres a nd thei r vari ati on i n space and t ime cou l d res u l t i n improved accuracy of i ce forecasts for the southern Beaufort Sea .

One of the stud i es i nc l uded here concerns the vari ati on of fl oe s i ze al ong the edge of the Arct i c pac k . Further study i n t h i s area coul d be of val ue because the amount of data avai l ab l e is spa rse . A broad-based study on s i ze frequency , pos s i b ly i nc l ud i ng temporal vari ati ons on a month ly basi s , woul d be perti nent to the des i g n of dri l l i ng p l atforms . Because of the nature of the offs hore i ce and i ts d i rect i o n of dri ft a study of t h i s type must be conducted i n the Beaufort Sea i tsel f where the exposure i s un i que . Stud i es of fl oe s i zes encountered i n other area s are not appl i ca­b l e .

60

9 . REFERENCES

Fu kutomi , T . , 1 958 . Arcti c Sea I ce . Nat i onal Academy of Sci ences , Nat i onal Research Counci l . Was h i ngton , D . C .

Mac Ne i l l M . and J . Garrett , 1 97 6 . Open Water Surface Currents , Dept . of the Envi ronment , V i ctori a , B . C . , Beaufort Sea Project Tec hn i ca l Report #1 7 .

Marko , J . R . a nd J . F . R . Gower , 1 974 . An As s es sment of the Users of ERTS- l Arcti c Imagery . Dept . of t he Env i ronment , Mari ne Sci ences Di rectorate , V i ctori a , B . C . Pac i fi c Mari ne S c i ences Report 74-8 .

Nansen , Fri tjof , 1 897 . Farthes t North . New York .

S hu l e i k i n , V . V . , 1 953 . P hys i c s of the Sea . Academy of Sc i ence of the U . S . S . R . , Mos cow .

Swi th i nbank , C . , 1 960 . I ce Atl a s of Arct i c Canada . Queens Pri nter , Ottawa .

Zubov , N . N . , 1 954 . Arcti c Sea I ce . C h i ef Adm i n i s trati on of the Northern Sea Route . Mos cow .

61

APPEND I X I

DETA I LS OF I CE BEACON DR I FTS

Date I ce Dri ft V i W i nd Vel oci ty Vw Speed Del fecti on Ang l e

Naut i ca l Wi nd Rat i o Degrees t o R i g h t

Degrees V i of W i nd M i l es Degrees Knots Vw

BEACON #2 near 7 00 N l 37 °W

J u ly 1 3- 1 4 050 2 . 0 0 70 1 0 0 . 006 1 - 20 1 4- 1 5 0 50 1 . 5 090 1 2 . 00 50 - 40 1 5- 1 6 1 26 2 . 0 1 00 1 2 . 0093 +26 1 6- 1 8 1 45 2 . 0 1 75 9 . 0045 0 1 8- 1 9 1 44 1 . 5 0 35 6 . 0 1 04 - 66 1 9- 20 306 4. 5 340 1 2 . 0 1 34 - 34 20- 21 342 1 . 5 340 1 0 . 00 6 2 + 2 2 1 -22 090 l . 5 1 1 5 6 . 0 1 78 - 5 2 2-24 09 2 3 . 0 090 1 6 . 0 1 89 + 7 24-25 1 1 2 6 . 5 Lgt Vrb 1 25- 26 1 35 0 . 5 Lgt Vrb l 26- 2 7 202 3 . 0 Lgt Vrb 1 2 7- 29 250 2 . 5 2 1 5 6 . 0099 +35 29- 30 2 84 2 . 5 1 80 1 2 . 0069 + 1 04 30- 31 360 4 . 0 1 25 9 . OOB5 --1 25

MEDIAN . 0096 - 2

B EACON # 3 near 70 0N 1 33°W

J u ly 1 3- 1 4 060 1 . 0 0 70 1 0 0 . 0072 - 1 0 1 4- 1 5 0 60 1 . 3 090 1 2 . 0049 - 30 1 5- 1 6 068 1 . 7 1 00 1 2 . 00 59 - 32 1 6- 1 7 096 1 . 7 1 45 1 0 . 00 59 - 49 1 7- 1 8 2 76 0 . 6 2 1 0 9 . 00 33 +66 1 8- 1 9 3 1 0 1 . 0 0 75 6 . 0067 - 1 25 1 9- 20 306 4. 5 340 1 2 . 0 1 39 - 34 20- 2 1 322 l . 7 340 1 0 . 0090 - 1 8 2 1 - 22 048 1 . 7 1 1 5 6 . 0098 - 6 7 22- 24 082 5 . 0 085 1 3 . 0080 - 3 24-25 072 4 . 0 Lgt Vrb 1 25-26 0 75 1 . 0 Lgt Vrb 1 26- 2 7 220 1 . 0 L g t Vrbl 2 7-29 223 5 . 0 2 1 5 6 . 0 1 98 - 8 29- 30 2 5 1 1 . 5 1 80 1 2 . 0040 +7 1 30- 31 263 0 . 5 1 25 9 . 0024 +1 38 31 -02 273 8 . 7 045 3 . 00 53 +32

Aug 02- 0 3 307 1 . 6 Lgt Vrb 1 0 3-06 089 6 . 0 095 6 . 0 1 09 - 6

MEDIAN . 0067 - 10

62

BEACON #4 near 70 ° N 1 33°W

J u ly 1 3- 1 4 0 30 1 . 0 0 70 1 0 0 . 0036 -40 1 4- 1 5 06 1 1 . 7 090 1 2 . 0064 -29 1 5- 1 6 0 70 2 . 0 1 00 1 2 . 0069 - 30 1 6- 1 7 1 10 1 . 0 1 45 1 0 . 0069 - 35 1 7- 1 8 290 0 . 5 2 1 0 9 . 0028 +80 1 8- 1 9 320 2 . 5 0 75 6 . 0 1 7 3 - 1 1 5 1 9- 20 286 3 . 0 340 1 2 . 0089 - 54 20- 21 31 5 1 . 5 340 1 0 . 0063 -25 2 1 -22 0 1 5 1 . 0 1 1 5 6 . 0069 - 1 00 2 2-24 0 1 5 1 . 0 090 1 6 . 00 1 2 - 7 5 24-25 1 95 0 . 2 Lgt Vrb l 25-26 1 95 0 . 2 Lgt Vrb 1 26- 2 7 1 80 1 . 5 Lgt Vrb 1

MEDIAN . 0067 - 37

B EACON #4A near 70 0N 1 35 °W

Aug 20- 2 1 2 38 2 . 2 0 55 1 2 . 00 7 3 - 1 77 2 1 - 22 0 1 7 0 . 5 Lg t Vrb 1 22- 2 3 1 87 3 . 0 1 25 1 3 . 00 89 +62 2 3-24 1 1 8 2 . 7 1 35 1 5 . 00 78 - 1 7 2 4- 25 1 80 1 . 5 1 35 1 8 . 0 1 59 + 1 0 5

MEAN . 0081 - 6

B EACON #5 near 70 0N 1 35°W

Aug 20- 2 1 267 5 . 0 0 55 1 2 . 0 1 8 1 - 1 48 2 1 - 22 260 8 . 0 Lg t Vrb 1 22- 2 3 0 1 0 2. 5 1 25 1 3 . 00 7 7 - 1 5 23-24 1 90 1 3 . 0 1 35 1 5 . 0 394 +55 2 4- 2 5 245 7 . 5 1 30 1 5 . 0 1 72 +95 2 5- 2 8 1 90 22 . 0 1 30 1 2 . 02 70 +60

MEDIAN . 0 1 8 1 +55

BEACON #6 near 70 0N 1 35 °W

Aug 20- 2 1 254 6 . 0 0 55 1 2 . 0208 - 1 6 1 2 1 - 2 3 352 5 . 5 1 25 7 . 0 1 54 - 1 33 2 3-24 1 95 1 6 . 5 1 35 1 5 . 05 2 1 +60 24-25 200 1 0 . 0 1 30 1 5 . 0 230 +70 25-28 2 1 2 4 . 0 1 30 1 2 . 0049 +82

ME DIAN . 0 208 +60

B EACON #8 near 70 0N 1 37°W

Aug 2 3-25 1 53 1 0 . 5 1 30 1 5 . 0 1 46 +23 2 5- 26 0 51 5 . 0 1 35 1 8 . 0 1 0 7 - 84 26-28 1 28 1 8. 0 1 25 1 2 . 0 295 + 3 28-29 1 6 3 1 0 . 0 Lgt Vrb 1

MEAN . 0 1 83 - 1 9

63 BEACON #1 2 near 70 0N 1 33°W

S ept 5-6 1 40 4 . 5 L gt Vrb 1 6- 7 OB7 6 . 0 1 50 20 . 0 1 0 3 - 6 3 7- 9 09 3 7 . 5 1 25 6 . 0260 - 32 9- 1 0 1 76 1 . 5 1 40 1 2 . 00 59 +36

1 0- 1 1 3 1 0 3. 0 Lgt Vrb 1 �lEAN . 0 1 41 - 20

BEACON #1 3 near 70 0N 1 37°W

Sept 6- 7 1 32 5 . 0 1 50 20 . 00B6 - l B 7-9 1 1 7 1 4 . 5 1 25 6 . 0550 - 6

MEAN . 031 B - 1 2

B EACON #1 4 n ear 70 0N 1 37 °W

Se pt 5- 6 0 75 3 . 3 Lgt Vrb 1 6- 7 1 26 3 . 0 1 50 20 . 00 54 - 24 7-9 1 2 1 7 . 5 1 25 6 . 02 B4 - 4 9- 1 0 1 36 24 . 0 1 40 1 2 . 0690 - 4

1 0- 1 1 1 27 1 6 . 0 Lgt Vrb 1 MEAN 0 . 343 - 1 1

B EACON #1 6 near 70 0N 1 35 °W

Sept 6- 7 1 35 6 . 0 1 50 20 . 0091 - 1 5 7- 9 1 1 1 7 . 5 1 25 6 . 0 255 - 1 4 9- 1 0 1 47 B . O 1 40 1 2 . 0 3 1 7 + 7

1 0- 1 1 279 4 . 0 Lgt Vrb 1 1"1 - 1 3 1 1 5 2 1 . 0 1 1 5 20 . 0 239 0 1 3- 1 4 1 1 7 33. 0 1 20 2 5 . 0440 - 3

ME D I AN . 0 255 - 3

BEACON #1 7 near 70 0N 1 33°W

Sept 6- 7 040 1 . 7 Lgt Vrb 1 7- 9 1 0 2 2 . 5 1 25 6 . 00B5 - 23 9- 1 0 1 31 5 . 5 1 40 1 2 . 02 1 B - 9

1 0- 1 1 30 5 3 . 5 Lgt Vrb 1 MEAN . 0 1 52 - 1 6

B EACON #l B near 70 0N 1 33°W

Sept 5-6 0 30 0 . 5 Lgt Vrb l 6- 7 100 6 . 5 1 50 20 . 0 1 25 - 50 7- 9 0 70 6 . 0 1 25 6 . 0 1 0B - 55 9- 1 0 1 55 7 . 5 1 40 1 2 . 0 29 7 + 1 5

1 0- 1 1 2B1 32 . 0 Lgt Vrb 1 1 1 - 1 3 1 1 9 29 . 5 1 1 5 20 . 0292 + 4 1 3- 1 4 1 1 9 2 3 . 0 1 20 25 . 0 30 7 - 1

ME D IAN . 0 29 2 - 1

64

BEACON # 1 9 near 700N 1 33°W

Sept 1 5- 1 6 2 30 4 . 5 1 1 0 25 . 0 1 06 - 1 50 1 6- 1 7 337 0 . 5 1 28 20 . 00 1 0 - 1 51 1 7- 1 8 31 5 2 . 5 1 1 5 1 0 . 0 1 08 - 1 60 1 8- 1 9 228 0 . 5 1 30 5 . 00 38 +1 58

MEAN . 0065 - 76

BEACON #31 near 70 0N 1 37°W

Sept 1 0- 1 1 35 3 3 . 0 Lgt Vrb 1 1 1 - 1 3 1 30 2 1 . 5 1 1 5 · 20 . 0 244 + 1 5

BEACON #32 n ear 70 0N 1 37°W

Sept 9- 1 0 1 0 6 1 7 . 5 1 40 1 2 . 0 584 - 34 1 0- 1 1 2 1 2 1 . 0 Lgt Vrb 1 1 1 - 1 3 1 1 0 21 . 0 1 1 5 20 . 02 44 - 5 1 3- 1 4 1 1 8 5 . 0 1 20 25 . 00 72 - 2

�1EAN . 0381 - 1 4

65

APPEND I X I I

WEEKLY C HARTS OF MED IAN I C E COND IT IONS

The fol l owi ng seri es of week ly c harts i s reproduced from the data conta i ned i n the FENCO report descri bed i n Secti on 1 . A p i ctori a l representat ion of the med i an amount of i ce has been attempted us i ng t he group i ngs of concentrat i on l evel s t hat appear to be mo st s i gn i ­fi cant .

Once the fa st i ce a l ong the Tuktoyaktuk Peni nsu l a breaks u p and d i s­perses i n t he fi rst hal f of J u l y , a l engthy open water per i od can occur . I n October , the i ncrea se i n i c e concentrat i on i s rap i d but th i c kness and strength of the fl oes are very l ow u nt i l the i ce reaches the 1 5-30 cm th i c kness range i n the second hal f of October .

Charts s howi ng med i an cond i t i ons duri ng the best years i n f i ve and duri ng the worst years i n fi ve are conta i ned i n t he deta i l ed F ENCO report referred to prev i ous l y .

,.

ME DIAN I CE CON CENTRATIONS

J UN E 4

�I L.3 � �

0-2 tenth s

3- 5 ten ths

j 72N ; r------------,i--.. _ __ .

§ �

6- 7 ten ths

8- 1 0 tenths

; I I I ! ;

I --lll�

I -.---

/,.\iI\j Q� �;f\� I

-.

. �� ; ' �t-.

- . '- ( -

1 40 jW ! i I

- ! f \ 1' ( "

. . , t- '

:�� SACr.S H AR50U R \ ,), ; i. .J-L/ /

.. ,/" ., ,

'--:::::':... -..

" J i " , I

,/ ,/ :,,i

' . - ",

I fl I \;-V( I I

, "

- --" ., . - -

'-.

1 2CW \

\

(J) (J)

ME DI P-N ICE CONCENTRATIONS

JUNE 1 1

: - - - 1 ! ! ' ; I , ' " 72N ! i i

-- - -t- .

r-' ! ' , tf' ;-+----�/'--r-��'-1s<;S -I I I i or I I I f \,.\"'\/ i J • I ' !

f I I r '" I "'" C:! i j ." p,, ! i i -r-�-I- _ _ I i

\ I \ . .\ ' I V

1 40 /W I

" '" � \ ' ----. -- l-- -�- -:-

! �W

"��r\ \ \ � 0 \ \ \ \

"�

/ /----/;\'(

\ \ ( ! ' S \ , )

)\J 1/ ACHS HARSOUR \\ '

I \' ) \ r�

\ " /L/ ./ \ (-! \ ; \

" \0�\ \ _-t-. __ � -r-'" _ _ ------r

I \ '\ I \

\ \ \ \ i

I

\ \

(j) --..J

U') U') ..c

..c +> +> c: c: OJ OJ +>

+> a

r--. I I U) 1.0 co

:z: [IJ] � a ........ I-

� co I-

:z:

U') U') w

..c u

..c +>

w +>

c:

:z: :z: c:

OJ

a :::;:) OJ

+>

U '""::>

+> W

N LO U ........ I I :z: a C"') c:r:

rn tJ ........ : : :

Cl

/ / w ::E

/ / . ' .

68

t:: - .4, .. .. . __ ' " . _ I I

� VI i--� --/' ;;:s:. , .� i "'0 't- -- ---� !

\ - � . -I

( J '.

---- ) . __ - 1--

! � I " �-... .... . - --1-----

. ). /

<"-. I N t r-- I I

- --- --. . -.-

I ij �. . � -2,ftl._ y _""""",," --=_,--:r-J

(/) z:: 0 >-< I-<::( 0::: I-z:: W U z:: 0 u

W U >-< z:: <::( 1-1 Cl w ::E

L!) N

W z:: => 'J

.� .

! i

i I I I i

69

t s +-7'"; -- -I -2. . l a i '6

- f-- -. - - - -� I -:;.. ! � I '-; , -1- -- ---. .

. _. __ .. I I f

/

- . � ..

, ,1- "

3: o M

.3: .� .. ----

�!I z/ . - 1;// I. q M I

� __________ � __ --�_/ _-_-·-___ ·_·�r���J�/ __ � ______ �!

MEDIAN I CE CON CENTRAT IONS

J ULY 2 i I . ----+--- - - -t ,

\ JIJ" " " : . . .. . .. . " " " " 1 '- " �I , , ,�

k=L __ . . r " S +

/ ;' I ! I i I

1--Zl..!i / l --7 -- -

: ---t i

I I I ___ ._ L�

I I

' �.

I I

I

, I I

, . , I

;._--+--I I . '

_ I ;i 1 \Jt ��JsV5 �I ' I I �

. 1\..\1':"1 ' .

0-2 tenths § 6- 7 tenths

3- 5 ten ths � 8- 1 0 te nths

"\ \ � I ---t---

. i . . . \ . .

. I · . .

I . \ "

. .

" : . . - -" ,,--\;i)) � \« u

\

\ \ \ \ \ \ \ /

!1 i ( . l ') { \rJ'

( I

1 40 /w ��\>-;� 0 1/' '0/( /1 ... . . I ' .... "',(:-0 . . U / 30W

rrmr.'A'S� � - � ���� & * g t p a! J rzmT!'B,.,m;I"'�l'''''''T'Jmmm: > : ........ rn7- I ' ",-;:"'.;;;rn:n. R?S'?""'Nil' .. ��m7':· (�(';o/;'I;"

-....J 0

� 't.,.

"

j;:: ·.·..:...7 I "

if) :z: 0 I-i l-e:( ex: I-:z: w u

;; u

w U I-i :z: e:( I-i 0 w ::E:

i , , -+_ ..

CJ)

>--' ::::> 'J

t..- .\., ---, - " .. - I _ _ _ _ ",-

-i -I i I

7 1

------

· t . ' - ' . .. -- , - , - � , ' '' ' ' ' ' -;i / *-

i \ \ \ ..1. . \

L . . � __ ._, __ __ � � " - 1-- , -i I I f--- --,-

� I ' _ r-•. ;

\ \,

_ \- --.-

I I / /

, 3: o N r-

.\,J

, . , , I I . I ·r r--- ···· -_.--.-

! I

)

3: " ?is .++-Y-....--, .. � =

j--_._ - -. " - . " ' -fl �-';';-!Nww-L-___ --'�-

.i. ' · . . � ' ." '

,---

� " "

< , .

-----_._-----,,--_._--_. -..

���-r-'

ME DIAN I CE CON CENTRATIONS

J ULY 1 6

I :.: :' ,: ,:::1 0- 2 ten ths g 6- 7 ten th s

I,'� ,' I 3- 5 tenths � 8- 1 0 tenths

, ,

. i

·Ji· .... �\ \ .

.:/ < "'-1 t o "

- - - - -- r-- ---

:,,-'

" , "

L __ _

.A; I

--, - -// !

I 7 21< , ! , i � _

I-------../'--------II' ----i-��\�\.r;) \- r---f , • c , ,

, . ()� ,

, /

ACriS H ARSOU R ( I '" " f"l/ ' 'v ( I

j-Z1tL ---

O�N !i +--­� .

\",-\1 . , /\.. .. I i f :

.. ! -- -r -"

; t ..

�, \ /' " ' \'---::-:

�-�-----

:>--1----!I

i I .J

'-J. ��,

, ) \ ' '' 1 f '

,

, I' � �,\ ("--/'/-- - " -

. ; , ; . ',� ,,,"'PEr' , I

1 :!OW

,"" ,,�

""-.J N

(/)

z:

0

>---f

� t:::l::

l-(Y)

z:

N

W

u

z:

>-

0

---l

u

�

r-::>

-.-rr1 _____ .

. -" -T· , .

\ .

. � .. .. � .. I� I I �

I -I !

--"

'-�

.. --._-

-..

I I I J

-L

f �/' r--

--

�/--

-I

"'-; . . \

-----t - ·· -

�--

) I �.--�

- ---. \

, MEDIAN I CE CON CENTRAT IONS

J ULY 30

I : .» :. :.:j 0- 2 tenths § 6- 7 te nth s

I I -=----Jj -·i -i -

, I

� 3- 5 tenths � 8- 1 0 tenths , ,, "

I

I I I I ,_

I I -+--- -----t-i

- �' " llcli ' -�

4 \ \ . I ' ! , I , I

�

! ! I , , � I i i i : . 1"' '' 11 . . .

7 2N I ! I ! ' I '\.. "" �

i +- -+-----r-----j<rs \F I i I I � f\\.., S I i

/ I · G� I'll ! ! i

( 1\'/ j.� - -

ACHS HARB

,

OUR \ \ \ I ' \.\1'\\! : . I " / ! -+-----11l� , I � _ _ _ _

1 40 j W I I

.. �.

\\ / ( rt . - \--Y-l- � \ . \ \ \ \

I

\ \ \ \ \

i \ \

_ . \ i

-\ , \

o

' \ "" \ ;

- - .

\ \

_. , ---_.-\- . _,--\ � L.)f �. \

.� ! . ,£APE( \ l '''. \ �y �(

-- "

I . PARRY , 12C;W \ - \ \ I \ \ I \

\

'-J �

MED IAN I C E CON CENTRATI ONS

AUGUST 6

i

"ltru " " '-�: \

I l-i----t J ! ! I

I

h'-

1 40 /W I I

, ' I I ! I I i I

! ,J;;;J� . . . . . . . . . _ . ACHS HARBOUj \\ - (

I /"'" ' , ! \ \ \ , , , \ I j : • I · • . . • ' , , I \ \ ' 1 - ' . . , " - i- " ' " , --�' i - -- -' \ \

. / . - . I " - . .� \ . . l \ \ � . . . . . , . . . . . � . . \� . . . \ \ \ /1 , , ';::Jl " - - o . '\ rk' \ .--• I \ ': .-- .- ,. , - -'-\ - �\-- I i A , \ \ �" \ \, - 'I�Q L.,�

'\.,,� ,\ , . : APE) : ' -t---. 1 . \ I r' \ ' \ 30W ' \ PAR� mw \

-......J (J1

ME DIAN I CE CONCENTRATIONS I AUGUST 1 3 /--1--, .: ... .. :.: .. { 0-2 tenths � 6- 7 tenths

I " .;.�I 3-5 tenths b.� 8- 1 0 tenths

i i

I + -

. J Y1- :�-t?3, ." \ , , , \ , . } , :') , . . � .oi i S

'" hr . ' \ «1; . "

.,,,� \

\ \ i \ \ ,.,-

I ,/ \ .r;' I /\ I '\ /' Y ( ! . I (

I ( ! 'l ._ r' I

I f---___. I I

I ! f I

I i -

• , • I. � . \ y: . . , . I i) -1------1L-< -I '

' • \ '

•

)\' ( ACHS HAR�OUR t\ . . -Lv

\ �) \ ( ! I

I / f-11!Lf--- -( I I ) � f

1 40 iw I I

\ . � • I :" " I "

\ - . . \ ' _ �

" '1 . ' ' \ ' ' . :, ' . � I _ . --- --- -

.- ---� I - · -- > �. · I�

·

· _ . . . j - - - . . .

c;

, i - . I - . ' ' - \ -I ' . '�

'j . ' I ' ' i _ - ' �'v - , . ,

i ' . I - ,

/ / 130 W

\ / \ - y-\ - -+- --\ \

� \ \ \ \ \ \

\ : i .

\ \

-.....J 0"1

/ " \

. +

VI

z::

0

I-i f-c::(

I 0:

: 0

f-

N

I z:

:

I w

f-

u

VI

z::

:::J

0

C!J

I u

::

:J

W

c::(

U

I-i

z::

c::(

I-i

0

W

:z

77

\ \

� ___ •. ---

--. _ . __ .. _J---..

t= jC.. -. ___ '." LtJl

. �

-­I A }

-� I .-.�--

.-f-._

-.-•.

j

z/ :'-l . .-��!� --. ----.-

.-�----.... ----_ -----)-

.--_.-.

-_.

/

---�f-;

.. �

, - ,

ME DIAN I CE CONCENTRATIONS

AUGUST 27

[ : ,: : .::·:1 0- 2 tenths

� 3- 5 tenth s , ' "

� 6- 7 tenths

"�I 8- 1 0 tenths

+

j

�v---� . ... '\ " "\

, '

" i'-

" , --..,...

, � -�

'" " '

i--I

'--';" , , , . - -.+--

i 72N : \f' I ------.. , .. -- -'7-.. _ .. , -1-_ - ,c,\'5 "

' , I , , " S ,

I " j /' "N t\�� :

' "

,.,� , I : : \�\1 \)� ,

I

... ! -.. ---i-- -'--- �

, '''C' S ACh�' \-\ AR�OU R '� r-----'-?

! --t--m , -i I\. ' r { , ' : _! : " i ... , �, �- i

.

. \ i I . - t- . -- - - -- ---"_. --t"·_· --� . .

� : i

'

'<J.. � . " . / ' ' i ! . ;

\>

" \,----.: . . -

r .� - '

� " . --1_ " '

,

' • • ,

, 'T _� , i . ' iJ ' ' :- '�,)N 'j 0 , 0

� , -4._ '

/,, ' 0

"-.. . 1 . I �' i - : " ,. '"' . '

r�. ' I ' ' I -:--�' i -- __ o_� ___ +-� lC=_-:"-V\ _- l��- 'v .' � 0 0 \o °-!!t°"; i,

'\ / 0 I ' I I / V y- � +-- , 0 '

.:: . . < � 0 . ' <;J' / � / . i ('. t- - - - -

" , o r .f i / I \.{ i 0 f ' (-'

, •

' '" ....... '< J I • c '

1 40 W \ __ � . �J:W0 ' 0 -"l?Jff 1 ' . . \ APE:7'\ )

" � � \ � I. ! ' "-: ' . I \

� . _ _

o� · ,' = "

',.

-<: ,., H:J-' <.. � ,

,_ �

,,§ � /, ' 3D. \ P ARRY "

. ..i )'"'L_-

, .. -..... -,. ...... ----.... , '-

"---

\;-'c..'"

, ..----

-, 'l-I

\-

1 20i-! \

'-J a:>

/ / J /

.\------___

___

__ ------1\---

. I

.

I _______ _ I

-__ --t------

--

--

--T

I

V>

z::

0

.......

(V)

I-«

r::::.:::

r::::.:::

I-w

-.-

._-

-_.-

z::

CD

w

::E

U

w

z::

I-0

D-

U

W

V>

W

U

.......

z::

«

.......

Cl

w

::E

79

1----________

__ : _

_ �-

--

i _____

.. -

3

' ---/'---1 _

_________

__ _

� .-

- - r

ME D IAN I C E CONCENTRAT IONS

SEPTEMBER 1 0

I :. '.:.:.:: I 0-2 tenths � 6- 7 tenths

I'� ��I 3-5 tenths � 8- 1 0 tenths

! ! I I

I , t---- -L _ _ _ I

'�I J I I rr-- J�\S � 1 + " 1)«.-* !

I I I J I '

'-. 1 �\rD "� \. \ \ I

\ /1 \ ) (' \ I -\ j) ') \ -r /

ACHS HARSOUR f\- t/ ) \ ( I . • \ \ 1:./ \ \ V� \ -----\-------

.. �---- -.\- \

\ \ '-\ \

\ \ \ \ \ \

\ \

\ \ \ , \ \ \ '

H\ \ L- -

------- -+ _.-' .-- ---- \

-

\ - . \ \ . �J � APe \ r�,,--\ -\ UV

I' \ PARRY i 20W \

\ I

1 40 IW

___ ........... 1.........,_ .. , I(�� � @," . ,/g'

co o

ME DIAN I e E CON CENTRATIONS

SEPTEt�B E R 1 7

. , I I 72Nt

/ ! I -L ; N ; �---- -, / �T-+-- .

t

_

l 40t ., '"'"'iTV7�I<"'��a::\?J:ZJA:::iL=j;"" ... ,t

1 I l

'( . ' .' "'\tIl \ " '-, \� vI � I I ! \ \ -+---i I I

>l30W

\ I:

\ \ \

\ 11 M-f ')

ACHS H ARBOUR � \ --t \ ;>L.-) \ ( -r\A-- � \ \

� �'�"�TI"""""""� ::::rz�.

C;. '

ME DIAN I CE CONCENTRAT IONS

S EPTEMB ER 24

I : : ":" ::J 0-2 tenths � 6- 7 tenths

� 3-5 ten ths � � 8- 1 0 tenth s

I

i I I I I - --j---, I I

I I I i I

I - - -j-- -I i I I ,v " 0 >° :(

�.-. -� "

" \"

"

". � " r 'J ! �·f \ c . "\ " 5 \ \ ' ,'

--r- L,<e; � +� Xl' " 'yL�i 0 0 �

I \ I .� - \ - -'---� / -" 1 "� - "r�-- : rr-

1 40/W I

/ n 30W \�PARRY

-� .�

/1

00 N

MEDIAN I CE CON CENTRATIONS

OCTOBER 1

·==== _________________ =-==�===_===m=======_== __ _=_==_=_ __

I -" ' 1-I I i

\

�-\lC) i \ v

\, \. \

.� \ / \ �.

� \ . ( ! \ /� = , -, I I \ / Y

, . i i ' ' / I

i I ! , ! I \ \ i , ! ! I :

'\ I I ! . I ' ) "J

I I � " " --..

f

'��-

1 40jW

I I I I \'" (

< �I 1 - AeHS HARSOUR(I\ T , Il' I ! ! ) v-v(

" , i \ �

r- I B ' " . I ),

. , ; ���+-�: �I ! . ��r-- - H' /;\ /

I I I\.\�\ i

1 - , . I , , I . � \ . -\ " \ \ \ , _ _ . . . 1 . ' . t'\ - \ \ ( . ;:'-' \ \ \

� 0 \ � ,

J! .J ) . \ 'VAP .. �/ -tc \�ARRY 1 20 W \

" ,, '""""'''''''''''''''''_ . -=-,""'='" MPI· ",",," '. _�

co w

ME DIAN I C E CON CENTRAT IONS

OCTOB ER 8 - ----j-------i I

"�u �'�

/ 1 :. :. :. : :. 1 0- 2 tenth s E -d 6- 7 tenths

r;'� �I 3- 5 tenths � 8- 1 0 tenths /!? ,. 'v / .

(/ I ----" r I I , ( i i

, ,: L, i�-/ ) I , (

, \ ACHS HAR60LJ R r;\ - - 1 \ ' . J �

, . ' ' \ ' ' \ , ' \ \ ;-u/ \ ( I I

()' i I I I \..\",\

i ! I

. I 1 .1 � I

f I ..f........J 1 N ; I ,

I � _ _ __ _ �_�� I

I , / ' , , F' ' � , " I ' . \ / \ \

, , , , � " � ' I , ' ' \ ' ...c----l- L.-V-+- .-+�.

I " 1 I ' I ' ' .

.

, . , '

, '

r ' •

, ! " ' / ' I ' • ' ' .,1 " : , , \ \ \ � I i . 1 , : ' . . <,.'\.. . ,I "

\ \ \

/ I i ?1) , '�' , '\ , .: ! \ \ " -�f _--+-_ - - _J- - -

o. I _

l' J---""')

I • "" to r

. , , 7' · ( '"",- \ 1<'0'n " ... n/ . ' /

�P �U "'----l 1 4Dt / [ �W \ P ARRY 1 20W \

\

(Xl +::>

I l / /

r- - - - - - -

)--

---

(/)

z

0

t-i l-e:(

0:

::: LO

I-Z

W

U

0:

::: Z

W

0

CC

U

0

I-

w

u

u

0

t-i Z

e:(

t-i Cl

w

::E:

85

-fwr .

ME DIAN I CE CONCENTRATI ONS

O CTOBER 22

1:- : ': ': : :1 0- 2 tenths § 6- 7 ten th s

j ,---�- t -I , I i ! I I I,' ,' � I 3- 5 ten ths � 8- 1 0 tenths I+ ___ � L�=-=---'-T------f------�=-=-�----�-=--==��f I I . .

1

I I I N . i --- -

" \ '-- '

\15 -\ \ "--''-\ \\ () � \ \ \ \ \ / \ /-:-\ /Y

\ I I , I I \ ; "--. 'i' / h - - - - --)

ACHS HARSOUR l \ l� " . A/ \ (

l _J+-- ·J--\ \ i ; \ \ \ \

\ ' \

� . � \ \ ' . � < --'t/ �� L \ (�---� \ E" �

PARR \

co (j)

87

y �

� �

-----�-I}--�-/

1 �

df<

I /

_---l;

.� f

-.......

Q...

,

----

---t--

! ,

, - ------

--�

---

---

---

--

--_t

--

----

---

I ,

!

----

----

---=11-+--

Vl

z:

<:)

f--i I--

<::::(

m

c:::

I--

N

... _-------

z:

W

u

c:::

z:

w

<:)

ca

u

<:)

I--

w

U

u

<:)

f--i

z:

<::::(

f--i 0

w

2:

� .. �

b 'IJltF'U

'!C 'C 15 '-' -

3:

-----

�