f

Ind ian Journal of Radi o & S pace Phys ics Vo l. :12. February 2003. pp. 43-5 1

Solar plasma activated decametric radio emission of non-fo origin from Jupiter magnetosphere

S K Bose* & A B Bhattacharya

Departme nt o f Phys ics, Kalyani Uni versity, Kalyani 74 1 235

Received 22 Jalll/ary 2002: revised received 20 JI/ lle 2002: accepled 4 Derober 2002

T he interaction between sola r pl asma with Jovian magnetosphere has been highli ghted by studying the corre lati o n between decametric rad io em iss io n fro m the Jupite r wi th di ffe rent solar pl asma parameters and a lso w ith the inte rpla netary magnctic fie ld fea ture and the he liospheric current sheet ex tent. S ignificance of the corre latio n is tested with usual stati sti cal techn iq ue. A lso the C hree-superposed-epoch analys is has been performed with lag-day s correcti on fo r the observed solar plasma parameters at I AU . conside ring high values of occurrence probability o f decametri c rad io-emi ss io n o f non-/ri o rigi n from J upite r as epoch days. T he results of C hree analys is support the corre lat ion study.

1 Introduction It has long been recogni zed that the vario us

processes on the solar atmosphere play signi ficant ro le in contro lling the inte rpl anetary and geophys ical di sturbances. Geomagneti c fi e ld vari atio ns have generall y been ex pl a ined o n the bas is of the interact ion of interpl anetary shocks with Earth's magnetosphere. There are number of simil ariti es between terres tri a l kilo metri c radiatio n (TKR) and Jovian decametric rad iation (J DR). S im ilar kilo metric rad io emi ss ion fro m Jupite r has been observed during the Ulys is-J upiter encounter. Kaiser and Alexander l

identi fied a beam of T KR measured in the magnetic local timc (MLT) wh ich is correlated w ith auroral emi ss ion index. Prang et al.2 correlated non-/o decametric (DA M) radio cmi ss ion observed from terrestrial stations with Jovian auroral event. Ka iser) pointed o ut that time variations of rad io emissions from Jupite r might be infl uenced by solar w ind . Bose and Bhattacharya4 showed local ti me dependence of non- /o Jovian decametric e mi ss ion observed from terrestrial stati ons at d iffe rent so lar activ ity period. Alexander el ai .5 analysed the data from Voyager I (V I) and Voyager 2 (V2) at the interval of o ne mo nth both before and afte r each Voyager encounter w ith Jupi ter and confi rmed that JDR is affected by Jov ian local timc. Also Jovian hectometric radio emission6

and solar wind control o n auroral radio emiss ion 7-9

have been reported. Plasma injecti on 10. 11 w ithi n Jupiter's inner mag netosphere near local noon has

*Dcpartlllc nt of Physics. Kalya ni Govt. Engg. College. Ka lyani 741135

been reported . Galileo Space-c raft as an orbite r or Jupiter scans DAM emi ss i o n l ~ fro m 0 h to 24 h in the Jov ian loca l time (JLT) range. From the observation o f Bose and Bhattacharya4 it has been revealed that local time dependence of non-Io related decametri c emi ss io n fro m Ju p iter (N IJD R) is due to different solar condi tio ns. A lso in several eve nts of NIJDR it was observed that the main cause of such emi ssion might be due to interaction o f interplanetary shocks

l1

w ith the Jupiter's magnetosphere. In the interplanetary medium the magnetic energy densi ty i~

much less than the ki netic energy density. Thus. to trace the mag netic and solar wind properti es o f an interplanetary region back to their source in the sn lar corona, one needs to know the ve loci ty vec tor (\f) (lr the solar wind at the point of observati on and dynami cs of the solar wind stream, viz. fl ux of soiar parti cles (NV) Lorentz fo rce (VB), so la r w ind dynamic pressure (NV\ proton density (N), etc. Lev ine £>1 (II. 14

showed a good connection between the S un and the Earth into a physical perspective.

In a number of papers I S-I'! it is ind icated that

decametric radio em ission of Jupiter is modulated hy so lar activity pheno mena. These papers inc lude fea tures of the sola r activity, like sun spot number. geomagnetic Ap index, interplane tary magneti c sector fea tures , solar w ind ve locity. etc . It was observed that the main cause o f N IJD R emi ssion is due to in teraction of in terplanetary shocks " with the Jupiter's magnetosphere. As the shock front is the carrier o f solar state, i.e. solar particles with randomly flu ctuating density . velocity and inte rplanetary mag net ic f ield (lMF), the present papcr is intcnded (0

44 INDIAN J RADIO & SPACE PHYS, FEBRUARY 2003

see how closely the different direct features [e.g. proton density (N); solar wind veloc ity (V); interplanetary magneti c field (B )] and the derived features [e.g. flu x of so lar particles (NV): solar wind dynamic press ure (NV2); Lorentz force (VB)] are respons ible for the non-Io related decametric emi ss ion from Jupiter. As the coronal ho l es~o playa key role in determining the spatial stru ctu re of the interplanetary magnet ic fi eld. it is also attempted to see the relat ion between polar coronal hole size (PCHS) with NIJDR. It is further observed that a main detail of the magneti c structure of the sun -interpl anetary medium ~; y stem is ,! he l iospheric current sheet that extends from the Sun to conjectured boundaries of the so lar wind21

. The three-d imensional configuration of the hel iospheric current sheet de termines the interplanetary magnetic field (I M F) sector structure. So. it is ,:\ so intended to see the relat ion between the heli ospheric current sheet ex tent (HCSE) wi th NIJDR .

2 Methodology Inves ti gati ons have been carried out with

deca metric radio signal from the Jupiter at 16 MH z monitored at different terrestrial stat ions of varying longitude and latitude~" . Such combinati on of data has helped to eliminate the effects of terrestri al rotation. It is found that larger part of observati ons of Jov ian decametri c rad iation (JDR) is made during daytime when terrestrial ionosphere is most di sturbed and opaq ue to lower frequency radiat ion. As a result beyond 100 days of opposition the data fo r Jovian decametric radiation fa ll s off sharply. We have, therefo re, used JD R data fo r ± 100 days from opposit ion only . The Jupiter' s satellite 10 related sources are separated out fro m non-Io sources using the defining co-ordi nate space of central meridian longi tude (CM L) I II (A.III) and superior geocentri c conjuncti ons of the Jupiter's satellite-Io as given by Carr and Desch ls. In the source region all the emissions are qual i fied as source (/0) emi ssions, including the non-source (non-Io) 'background ', i.e. the non-source emi ss ion which certainly would be observed if the source did not ex ist. However, numerous emission events are recorded which cross the limiting values of la-sources and overlap both types of la -related and non-Io related sources. In this analys is. all types of overlapping cases have been rejec ted. Bose and Bhattacharya4 showed that 10-sources have no statistical significance with solar ac ti vity. but non-/o sources have the high stati stical significance. So, an urge has been felt to re-evaluate

and inves tigate the physical mechani sms uncierl ying the modulation of decametric radio em iss ion from Jupiter in the so lar magnetosphere. To re-eva luate Ih l' phenomenon the analys is has been sought into two parts. In the first part, long term modul ation has becn searched in finding the co- relation betw en non-/(1 related decametric radio emi ssion from Jupiter wi th different solar acti vity parameters. In the seco ne! pa rI. Chree's superposed epoch anal ysis is done with dail y mean values of solar wind velocity at the Jupiter' s orbit by correcting the lag days for the arri val of sa me so lar wind plasma observed at I AU with hi gh va lu es of occurrence probability of NIJDR as key days.

The non-/o deca metric emission ac ti vity from Jupiter on a given day ;, characterized by the occurrence probability defi ned as :

1 O.P.=­

T

where, 1 = Total duration of emission on any day. and T = Total time of observati on on that day.

... ( I l

We have considered twelve apparitions anci. in each appariti on, two data have been calcul alcd--{)ne for the average of O.P. for 100 days before-opposi ti on and the other for after-opposition fo r same days or interval. Solar plasma data are taken fro m interplanetary medium data book ~:1. Polar coronal hole size data are taken from Hundhau:;,en el {{ ( fl .

Heliospheric current sheet data are taken from Korzhov21

. The averages of solar data for I 00 day~ before and after opposition have been ca lculated 1'0 1'

the correlation analysis.

3 Results 3.1 Correlation analysis and results

In Fig. I (a), NIJDR O.P. values (two values I'm each apparitions) plotted against the corresponding twelve apparitions and in Fig. I [(b), (cl and dl basic solar parameters, e.g. mean solar wind veloc ity ( V ).

mean proton densi ty (N) and mean in terplanetary magnetic fi eld (lMF) (8) are shown. In Fig. 2[(a). (b)

and (c)] mean values of the deri ved parameters. e.g. solar wincl dynamic pressure (NV") . fl ux of sola r pl asma (NV) and Lorentz force ( VB) have becn plotted against the corresponding same appari[ i on ~ a~

mentioned earlier. In Fi g. 3[(a) and (b) I mean ex tent of heli ospheric current sheet ex tent (HCSE) and pobr coronal hole size (PC HS) have been plorted aga in~l the same apparitions as in Fig. 1. The trend of the

t

BOSE & BHATTACHARYA: SOLAR PLASMA ACTIVATED DECAM ETRIC RADIO EMISS ION

8

4

0 _ 60 , ~

~ 50

~ 40 o ~ 30

C

0

0

0

~ LO <5

0 III

.., 'E v

~ in z .., o z !? o .. 0.

0

8

6

4

2

0

oQ ( 0)

, ?\ P" ,J> to'

.0, 0 , 0 ---0 -q C.P.

P. " , , b

00. --Ai , " tl , u. , .<p tJ

0-

( b)

° OQ

I ,

'I I , , I I I V

p O" , I I

t"o" I iJ :' % -"0-0" " .01),

, bu. ' 'O'0 cf'-'" o

, 'OJ

(c) p- - -{)V

\<, , -0

P- O N

c?-_D I , 'cP,-d ° cJ

1). " -cA, Q , , , 1).--0-<1

,

'O<T

;;: 6 ~--Q £)0- - ..0" ( d ) .oO-Q / 0- . ''' ''00' .- 'ty

I

%' ! 1 u ~ - , ~ 0 .., '" ~ 4 , ,

,FQ, 0 " , '. P, 0- -_0

o \ d

1965 ' 66 ' 57 VEAR

Fi g. I- Curves showi ng the (a) Non -10 Jov ian decametric mean occurre nce probabil ity, (b) Mea n solar wi nd veloc ity (V), (c) Mean proton density (N) and (d) Mean inter-planetary magnetic fie ld (B) against the correspondi ng apparitions from 196.5 to 1978 (two va lues about ± 100 days of opposit ion in each apparitio n)

18

N

' ~

· 14 c ~

",0

'7~ 10 · N

> z

6

' u · N ~ 30

' E v ~

~ 10 > ?

7" 40 E 0 , e 30 c ~

~o

I~ 20 OJ >

1965

(c)

: D-Q\ o 0. , \0

R , Q " -oO - -OO-- -<J / b' tr \. 0 :' 0 ' O- --<Jd .

67 69 71 YE AR S

73

'. o- -D 0-

75 77

Fig. 2- Curves show ing the (a) Mean solar wind dynam ic pressure (NV ~ ). (b) Mean nux o f so lar plasma (NV) and (c) Mean Lorentz force (VB) agai nst 1965 - 1978 apparitions (two values

about ± 100 days of opposition in each apparition) derived parameters from so lar wind

( 0)

'" 30 . " 0- -

'7 1

YEAR S

' 73 ' 75

, I

' 77

Fig. 3- Curves showing the (a) Mean he liospheric curr<:n t , 11':<:1 extent, (b) Mean polar coronal hole size against f 965-7:-: apparitions (two values about ± 100 days of opp()s iti ()n ~ in <:;lcl1 apparit ion) characte rist ic fe<l ture of solar wind

temporal variation of O .P. w ith other curves related with solar fea tures leads us to inves ti gate the phenomena with linear correlation analysi s. As we arc observing the long te rm modulation with corre lation analysis, we divide the whole data set into two separate sub-sets according to the pol arity state or the solar mag netic field which has been reversed in the 1969-70 pe riod . So, the two sub-sets are: (i) suh~l't

from 1965 to 1970 under the condi lio n of northe rn field points towards the Sun (- I +, pre 1970) and (i i) subset from 1971 to 1977 under the cond it ion or northern field poin t away from the Sun (+1- . po" t 1970).

The above mentioned two sets of data have heen used to find the corre lation coeffic ient separatel y in two sets between O.P. and sola r parameter" as mentioned earlier. For calculatio n o f corre lation coefficient, we have used the relation as

... en

where, r = Linear correlation coefficient

X = Parameters responsible for the pheno meno n under investigation (viz. occurrence probability)

Y = Other parameters (e.g. solar wind. e tc.)

X, Y = Respecti ve means

Significance test: The statistical sig nificance of the corre lation

coefficients have been searched with the I-stati s ti cs or

46 INDI AN J RADIO & SPACE PHYS, FEBRUARY 2003

the distribution of correlation coefficiene4,which is gIven as

r./15

f = ---=-- -(1_ r 2 ) os

. . . (3)

where, f = (11-2) , the degrees of freedom with which the quantity is di stributed as / and /I the number of the data po ints. From Eq.(3) for a particular degree of freedom, the value of r can be calculated for different va lues of f fo r d ifferent statistical sig nificant level25 as

( .r J-O

.

5

r = 1+-, f -

. . . (4)

The correlati on coefficients be tween O .P. and solar wind parameters are shown in Table I , while the results of significance tes t are shown in Table 2.

From Table I , it has been revealed that the correlati on coefficient is relativel y higher under the cond iti on of no rthern field points towards the Sun (- / +, pre 1970) than away fro m the Sun (+ / - post 1970). Regarding the sig nificance level from Table 2 it can be sa id th at correlat ions of O.P. of non-Io DAM with di ffe rent solar parameters, specifically, PCHS, HCSE, so la r wind dynamic pressure and solar flux are hi ghl y significant, whereas the level of significance is les. in case of the parameters like magetic field (B)

for both the periods [1965-70 and 197 1-77]. Though the level of sig nificance for solar wind ve locity (V) and Lorentz force (VB) is 0 .05 fo r the periods 1971 -77 and 1965-70, respectivel y, the sig nificant level of these two parameters are less than 0 .05 for the alternate periods, respectivel y.

In the second step, to see the phenomena in the environment of Jupite r's magnetosphere, we tried with Chree's superposed epoch analysis with velocity ex trapo lated to 5 .2 AU by calcul ating lag days between the day of recording data for solar parameters at ! AU and the emission of DAM from Jupiter at 5.2 AU with O .P. of non-fa DAM as key day.

3.2 Chree's superposed analysis and results

C hree's superposed epoch analysis is performed wi th hi gh val ues of O.P. as key days and daily mean solar wind velocity as the superposed quantity. Because of changed geometry of Earth-Sun-Jupiter position, the peak of the solar wi nd velocity in Chree diagram wi ll be away from the key day or zero day by

Table I--Corre lati on coeffici ent belween O.P. ;Jnd solar parameters

Figures Solar Correlation coeffi c ients for the p..:ri (lu considered parameters 1965-70 197 1-77

(r1) ( ,.~ )

I(b) V 0.46 0.51 I (c) N 0.65 0.47 I(d) B 0.38 0.13 2(a) Nv2 0.79 0.73 2(b) NV 0.74 o.n 2(c) VB 0.59 0.3X 3(a) HCSE * 0.92 3(b) PUIS 0.91 0.65

*The dala for HCSE were not ava ilable for that period

Table 2- Stati stical significance of the correlation coeffi cient using l-st;Jti stics

So lar Significance at degrees of freedom «(= 1/ - 2) X parameters and 12, respectively. for thc pcriods

1965 - 70 197 I - 77

V 0. 10 0.0,) N 0.025 0.05 B 0.30 0.60 NV2 <0.01 '= 0.00 I NV 0.015 '" 0.001 VB 0.05 0.2 HCSE « (LOO I PCHS < 0.001 0.01

different lag days . The lag days are the time de lay (8. f ) for the solar plasma to trave l fro m the Earth to J upiler.

This time interval (8./) between the arrival of pl asma to the Earth and that at Jupiter may be written as

... (5)

Posi tive sign before the second term is for periods before the opposition and negati ve sig n for periods afte r the oppos iti o n. Here, dJ and dE are mean di stances of Jupiter and Earth from the Sun . respecti ve ly, V the solar wind radi al velocity which is a lmost unmodified26 between I and 8 AU , 0 the angle between the S un-Jupiter line and Su n-Earth linc (0 = 0° at opposi ti on) and UJ the angular velocity or solar rotation . T hus, 8.{ is positive when so lar wind plasma-stream is recorded at 1 AU earl ier than it reaches Jupiter and is negati ve in the opposi te casco When the solar wind is long lived and persists ovcr o ne solar rotation, secondary peaks are ex pected at delay ti mes in days as

... (6)

;

BOSE & BHATTACHARYA: SOLAR PLASMA ACTIVATED DECAMETRIC RADIO EM ISS ION .+7

25.4 days being the sidereal period of solar rotation and k the number of solar rotation.

Adding these lag days (1'1/) to the day of observation at I AU, we get the time (day) when the same plasma reaches the orbit of Jupiter. Day-to-day va lues of solar wind ve locity (V) at Jupiter are thus obtained . Chrcc analysis is then performed with these ex trapolated solar wind velocity as the superposed quantity and high values of a .p. as epoch days or key days. Thi s is done for all the individual apparitions both for before-opposition and after-opposition periods. Due to discontinuous data for after­opposition pe riod in the year 1969, 1970 and 1971 , the Chree analysis for these three years are performed with before-opposi tion period data only. Figures 4-15 show the Chree analysis diagrams for the period 1965-77.It is found that the peak value of ex trapo lated solar wind velocity obtained by caiculating lag days falls e ither on zero day or at least wi thin four days from zero day.

The stati stical sig nificance of the results shown by broken lines in Figs 4-15 is evaluated separate ly for each peak following the procedure of Bell and

Galzer27, using the standard e rror (0-' )

(J (J' =

.JNI/.' . .. (7)

where, (J is the standard dev iation for the solar wind

ve locity data within ± 100 days of opposition, N the number of superposed values corresponding to each

peak and 1/' = 5 for the running average employed for smoothing. Confidence level of 99% is then estimated

using I-stati sti cs at ! fUl I 0-' . From the careful analysis of Figs 4-15 fo llowing

points can be summari zed. With respect to the key day corresponding to high occurrence probability of non-Io DAM from Jupiter, the peak value of the superposed solar wind velocity extrapolated to 5 .2 AU at Jupi ter occurs earlier, i.e. negative lag days (maximum 3-days) for almost in all apparition (Figs 4-7 , pre-1970 period) except in the year 1968 (Fig. 6) where lag days after the key day (+ 2 days) before opposition and on the key day after opposition, 1968 . In the transition period of solar polar fi e ld reversal from. - / + to + / - 1969-70 period (Fig. 8) lag days are - I day and - 3 days. Similarly, in the state of solar polar field away from north pole, the lag days fo r a ll appari tio ns are - ve (maximum - 4 days) [Figs 9, 10, 12. 13 and 15(a)] except for the apparitions presented in Figs 11. 14 and 15(b). The +ve and -ve

'11/1 E 700

.:£ >-~

I­U o -.J W > o z ~

600

500

700 (b) (a)

600

500

0:: « -.J o (J) 4 0 0 4 0 0 L..L....J.......J,--,-..L...JL-L-..L...l--'

-S -3 -1 0 1 3 5 -S -3 -1 0 , 5

LAG DAYS

Fig. 4-Curves showing the superposed so lar wind \'elocil y ex trapolated to 5.2 AU at Jupiter (SSWVJ ) aga inst lag dav~ considering high O.P. of NIJDR as key day in the year 19651(;1) After opposition . (b) Before opposition I

11/1 E

.:£ 500 ~ I-

U o -.J

w 450 > o z ~ 0:: 400 « -.J o (J)

( b ) 196 7

__ ~_ .. (aL 600

500

400

350 300~~~-L~-L~ -5 -3 -1 0 1 3 5 -5 -3 -1 0' 3 5

LAG DAYS

Fig. 5-Curves showing the SSWVJ against lag days consideri ng high O.P. of NIJDR as key day in the year 1967 I(a ) After opposition. (b) Before opposition 1

11/1 E 550

.:£ >-­I-

g 500 ..J W > o z ~ 450

0:: « -.J

500 ( b) (0)

450

400

~ 4 0 0 L-L---'--''--'--'--.......... --'----''--' 3 5 0 L.L-'-.L...l--'--'---''--'---'---'

- 5 -3 -1 0 1 3 5 - 5 -3 -1 0 1 3 5

LAG DAYS

Fig. 6- Curves showing the SSWVJ against lag days CCJn~ idc rill ~

high O.P. of NIJDR as key day in the year 1968. [(a) After opposition. (b) Before oppositionl

4R INDI AN J RADIO & SPACE PHYS. FEBRUARY 2003

1969

55 0 IV)

E .Y

~ I- 500 u 0 -.J W > 0 450 z ~ 0:: <{ -.J 400 0 (J)

3S0LL~LL~-L~-L~ - 6 -4 -2 0 2 4 6

LAG DAYS

Fig . 7- Curves showi ng the SSWVJ aga inst lag days considering high 0.1'. as key day in the year 1969 (Before oppos itio n)

'TV) E

-'<: ;r"

I­u o

600

G:l 500 > o z ~ ~ 400 _J o (J)

- 6 -4 -2 o 2 LAG DAYS

4 6

Fig. X- Same as Fig. 7. but for 1970 (Before opposition)

1000 1971 IV)

E - --~ - ---'<:

~ 8001-I-u 0 -.J W 600 > 0

~ z :s 0:: 400

~ « -.J 0 (f)

200 I

-6 -4 -2 0 2 4 5

LAG DAYS

Fig. lJ- Sallle as Fi g. 7. but for 1971 (I3efore oppos ition)

E

;r

'= u o ~

w > o z 3:

750 750 (bl

650

550

~ 450 ~

o U)

350~-L~-L~-L~-L~-L~350 -8 -6 -4 -2 0 2 4 6 8 -4-2

LAG DAYS

o 2 4

Fig. IO-Curves show ing the SSWVJ against lag day~

considering hi gh 0 .1'. as key day in the year 1972 I (al Arter opposition, (b) Before opposition I

600 E

>­I- 500 u o -.J W > ~ 400 ~ 0:: <{ -.J

1973 500 1973

450

400

fX 3 0 0 L-.1.-L..L..JL...J...-'--'----'--'--.J 3 5 0 ,---,--,-..L...J.-L-..L-J'---'--'--'

-4 -2 0 2 4 -4 -2 o 2 4

LAG DAYS

Fig. II-Curves showing the SSWVJ against lag day~

considering high 0.1'. as key day in the year 1l)/3 I (al Aftc:r opposition, (b) Before opposition]

IV) 700 1974 700 E .N.Z4... ( 0) .Y ( b) ~ I- - - - -- - -- -

u 600 600 0 ~~~~ ~ l~ ~~~--.J W > 0 z ~ 500 500

\ 0:: <{ -.J 0 (f) 400

-4 -2 -4 - 2 0 2 4

LAG DAY S

Fig. 12-Curves show ing the SSWVJ against lag da\, considering high 0.1'. as key day in the year 1974 Ilal All er opposition . (b) Before opposition I

...

r

BOSE & BHATTACHARYA: SOLAR PLASMA ACTIVATED DECAMETRIC RADI O EM ISS ION

,~ 500 r------19~7~5~----~ E (b)

.:£

~ /---u 450 o -' w > o z ~ 400 a:: « -' ill 350

_L6L_~4-L_L2~0-L~2-LL4~6~

500

450

400

- 6 -4 -2 0 2 4 6

LAG DAYS

Fi g. 13- Curves showing the SSWV J against lag days considering high O.P. as key day in the year 1975 [(a) Arter opposition, (b) l3efore opposition I

IV) 500 l.92.fi 500 E

( b)

.Y

>-I-

450 450 U 0 -l W > 0 z 4 00 400 ~ a:: <{ -l 0 350 3 50 Ul

- 4 - 2 0 2 4 -6 -4 -2 0 2 4 6

LAG D AY S

Fig. 14- Curves showing the SSWVJ aga inst lag days considering high O.P. as key day in the year 1976 [(a) After opposition. (b) l3erore oppos ition I

800 1977 (b ) 550 197 7 1

1Il· - -------

____ (0 L

E .Y >--

700 500 I-

u 0 -l w 450 > 600 0 z ~ a::

500 400 <{ -l 0 Ul

400 350 -4 -2 2 4 -4 · -2 0 2 4

LAG DAYS

Fig. IS- Curves showing the SSWVJ aga inst lag days con, iciering high O.P. as key day in Ihe year 1977 (a) After opposition. (b) l3efore opposition I

lag days for the peak value in the Chree' s superposed epoch analysis with solar wind velocity ex trapolated to Jupiter orbit for the hi gh decametri c ac ti vity as the key day can be ex plained with the sector bou ndary or the interplanetary magnetic field ori ginating on thL' Sun and is usually accompanied by sharp var i ati on ~ or the so lar wind velocity (V), by proton densi ty (N)

fluctuat ions and magnetic field changes. The turbule nt regions are often assoc iated with the sector boundar) of IM F. The turbu lent area associated with IMF i ~

stretched radi all y into interplanetary space startin ,g from the Sun with the form of the Archimedcan spirals associated with the sector boundary and interacts wi th the Earth's magnetosphere inj ect ill ,g energy into the magnetospheri c fields and particl e~ .

which are recorded at I AU. After (or prior to) a certain interval the turbul ent region also hits the Jov ian magnetosphere. Two kinds of time delay or la,g time occur in combination wi th the turbul ent reg i () n ~ .

The first is the case of the succeeding interacti oll where a turbul ent region encounters one of the pl anets (the Earth or Jupiter) and the same turbul ent reg ion later encounters the other planet. The second is the case of alternating interacti ons where th e succeedin ,g encounters of the turbulent regions with two planets take plaee for different turbulent regions. In thi s ca~e .

four possibiliti es may be considered for illlerprcting - ve and +ve lag days.

(i) If one turbulent region interacts with the Earth prior to the encounter of the second region wi th Jupiter, then the time lag wi ll be - yeo

(ii ) If first turbulent region encounters Jupiter prior to the encou nter of second region with the Earth later, then time lag will be +ve .

(i ii ) I f the second region encounters Jupiter prior to the encounter of first region with the Earth. time lag wi ll be +ve.

(iv) If the second region hits the Earth prior to the encounter of the first region with Jupiter, the time lag will be -yeo

4 Discussion The work reported in -the paper is based on the data

recorded during the peri od 1965-70 for fi ve appari tions providing 5x2 data points and also for th e period 1971-77 for the seven apparition. provi d in ~

7x2 data points. There is an attempt to justify the significance of correlation between NIJDR and so lar parameters using so me usual stati stical techniques. A carefu l exploitation of the data has been able to

50 INDIAN J RADIO & SPACE PHYS, FEBRUARY 2003

con firm that some correlation coefficients are highly significant and some others are not.

The corre lati ons of non-/o decametric emissions from Jupiter with solar parameters, viz., olasma density (N), solar wind velocity ( V) and IMF magn: tude observed by Voyager I and Voyager 2 during 1979 close to Jupiter have been investigated by Barrow ef at. 28 and they found some correlation. although the precise details of relationship are not ascertained. The local time dependence of the /0 independent component observed by Galileo had been analysed by Meniette el 0 11 2. Analys is with the three space craft PI O, P I I and Ulysses data had been done by Tsuch iya ef of. 29 and from their analys is we get evidence that Jovian magnetosphere is controlled by the polari ty of IM F. The solar wind exerts a strong inlluence on the Jov ian magnetosphere in changing its volu me by its dynamic pressure (NV2

), in energiz ing plasma and in sti mulating the aurora and a host of other assoc iated effects, e.g. rad io wave emission, have been reported recently by Southwood and K · I 10 .

I vc SOIl" by analysrng the data of the space crafts, the Gali leo and the Cassi ni.

Ana lys is of satell ite observed data enriches our knowledge, bUI avai lab le such data are fo:- small ti me scales. So, to investigate the phenomenon, the long period data, which can only be obtained from ground based observat ion, are needed . Among the differ nt parameters of solar plasma, particu larly, solar wind dynamic pressure (NV2) has a high correlation (more than I % significant level). Besides th is, other parametes, viz. solar wind velocity (V), fl ux (NV), Lorentz force (VB) also show a relatively good con·elation. It is a well known fac t that coronal hole is the source of high speed solar wind which carries frozen-in magnetic field with three-dimensional IMF struct ure. The con tour of the zero radial field3 1 on the source surface is defi ned as the location of the he!iospheric current sheet and is extrapolated into the solar wind . It has been seen from Table I that the occurrence probability of non-Io DAM has a high correlation with polar coronal hole size and heliospheric cu rrent sheet extent, both having 0. 1 % and 0.00 1 % significant level. Besides the above con·elation, the solar wind data extrapolated to Jupiter 10 Chree's superposed epoch with non-/o Jovian decametric activity as key day show peak values of the extrapolated sol ar w ind ve loci ty with -4 to +3 days lag, whieh has been explained by successive crossings (either Earth or Jupi ter) of the tu rbulent region of lMF sector boundary.

All the above evidence and the reported res ult s ·~ c or analysis with the space craft data and magneto-hydro­dynamic simulation3J

.34 of the effect of the solar wind on the Jovian magnetosphere confirm that Jovian magnetosphere is perturbed by solar plasma reported features, especially, solar wind dynamic pressure ;.IIlci

IMF lines. In case o f in teraction of lMF lines with Jovian magnetosphere it has been observed from our analysis that during the period of northward IM F interaction with the magnetosphere the corre lati on coefficient is higher in compari son to thaI for southward IMF interaction. Also, it has been mentioned in thi s analys is that IJDR ha. a significantly high correlation with he li ospheri c current sheet extent and polar coronal hole size. All such observations indicate that solar wind s t ru ct lln:~.

which influence Ihe dynamics of Jup itei·· " magnetosphere, in turn, control the radio emiss ions or non-Io o rigin in the decametric range generated in the magnetosphere.

Acknowledgements The authors wish to thank the Director, World Data

Centre-A, for supplying decametric radi o observatioll data and tape containi ng solar wind data. T lll'\' expressed their gratitude to Prof. John M Wilcox r(;1" sending data regard ing IMF sector bl1undary crossing at the Earth. The authors are also grate ful to their respecti ve Heads of the Departments for their encouragement and providing facil ities. Spec ial thanks are due to the anonymous rev iewers of th is paper for the ir valuable critical com ments.

R eferences I Kaiser M L & Alexander J K. J Ceophv.1 Res (US/\). X2

(1997) 3273.

2 Prang R. Zarka P. Ballester G E. Livengood T A. D':l1i ~ I .. Carra T. Reyes F. Bannc S J & Moos H W. J GeofJhn Re.1 (USA). 98 (1993) 18779.

3 Kaiser M L, J GeoplJys Res (USA), 9X ( 1993) I X7)7. • 4 Bose S K & Bhauacharya A B. I lldiall J f?adio & .. "({("('

Pilys. 30 (2001) 233. 5 Alexander J K. Carr T D. T hie man J R. Schau hie .I J 8:

Ridd le A C, J Ceophys Res (USA), R6 ( 19R I) X529. 6 Lardre iter H P & Leblanc Y. AIlII Ceopln·.I· (Frallce). l)

( 1991) 784. 7 Lardreiter H P. Zarka P & Lecacheu x A. Phlllel & Spun' Sci

(UK ), 42 (1994) 9 19. 8 Baron R LOwen 1'. Connerney J E P. Sawh T & H~JTin~ll\ll

J, lcarus(USA), 120 ( 1996)437. -

9 Saloh T. Connerney J E P & Barron R L. lcam s (USA I. 122 (1996) I.

10 Mauk B H, Williams D j & McEntire R M. C('ophvs Res 1.1'11

(USA). 24 (1997) 2949.

BOSE & BHATTACHARYA: SOLAR PLASMA ACTIVATED DECAMETRIC RADIO EM ISS IO 5 1

II Krupp N. Woch J, Lagg A, Wilken B. Livi S & Williams D, Ceopitvs Rl's Lell (USA). 25 ( 1998) 1249.

12 Menietti J D. Gurnet D A , Kurth J & Groene J B, Ceophys Res Lell (USA). 26 ( 1999) 569.

13 Oya H & Morioka A. Planet & Space Sci (U K), 29 ( 198 1) 783.

14 Lev ine R H, A ltschuler M D & Harvey J W, J Ceophys Res (USA). 82 ( 1977) 106 1.

15 Carr T D & Desch M D, Jupiter, edi ted by T Gehrels (Uni v. of Ari zona Press, Tucson), 1976, pp. 693-735.

16 Barrow C H, Planet & Space Sci (UK), 26 (1978) 11 93. 17 Barrow C H, J Ceophys Res (USA), 84 ( 1979) 5366. 18 Terasawa T. M aezawa K & Machida S, Nature (UK), 273

( 1978) 131. 19 Pokorney Z. Bul/ Astron l/lSt (Czechoslovakia), 33 ( 1982)

193. 20 Hundhausen A J . Si me D G, Hansen R T & Hansen S F,

Sciel/ce (USA). 207 ( 1980) 76 1. 2 1 Korzliov N P. IS''' Intem ational Cosmic Ray COl/j erence.

MG 3 ( 1983). p. 106. 22 Thieman J F. NASA Techl/ical Memorandum. 8308, 1979. 23 King J H. Interplanewry Medium Data Book. NSSDC/

WDCA R & S 77-04, GSFC, Green Belt (USA), 1979.

24 Hald A . Statistical Theory Il'ith Enginl'l'ring Applil'lltio//.\ (NY). (John Wiley & Sons. Inc. London). 1952.

25 Hoel P G. Int m dllction 10 Mathematical Stmistics (NY). (John Wiley & sons, Chapman & Hall Ltd . London). 1947.

26 T homas B T & Smith E J . .I Ceophvs Res (USA). 86 ( 19X I )

11 , 105. 27 Bell B & Galzer H. Smiths(Jlli(/II COlliI' Astmph.",\' (US!\). 2

( 1957)51. 28 Barrow C H, Desch M D & Genova F. I\st/'{III Astmphl'.l

(UK), 165 ( 1986) 244. 29 Tsuchiya F, Morioka A. Misawa H. Ea rth Planets Spac('

(Japan). 5 1 ( 1999) 987. 30 Southwood D J. Ki velson M G. J Ceophrs Res (USA ). 1()6

(200 1) 6 123. 3 1 Hoeksema T J, Wilcox J M & Scherrer P H. J Ceoph.l'.\ Re,\

(USA). 88 ( 1983) 9910. 32 Reiner M J, Kai ser M L & Desch M D. Ceophvs Rl'.I' Lell

(USA). 27 (2000) 297.

33 Miyoshi T, Kusano K. J Ceophys Res (USA) . 106 CWO I ) 10723.

34 Walker R J, Ogino T & Kivelson M G. Plal/et & Space Sci (UK), 49 ( 1999) 237.