intense surface cyclone activity in the arctic during the 2005 – 06 and 2006 – 07 cool seasons

Intense Surface Cyclone Activity Intense Surface Cyclone Activity in the Arctic during the 2005in the Arctic during the 2005––06 06

and 2006and 2006––07 Cool Seasons07 Cool Seasons

Brian Silviotti, Lance F. Bosart, and Daniel KeyserBrian Silviotti, Lance F. Bosart, and Daniel Keyser Department of Earth and Atmospheric Sciences Department of Earth and Atmospheric Sciences

University at Albany, Albany, New YorkUniversity at Albany, Albany, New York

NSF Grant ATM-0434189NSF Grant ATM-0434189

1010thth Northeast Regional Operational Workshop Northeast Regional Operational Workshop 5 November 20085 November 2008

MotivationMotivation

Arctic cyclones not Arctic cyclones not extensively studiedextensively studied

Intense arctic cyclones Intense arctic cyclones

pose economic hazards, pose economic hazards,

especially to shippingespecially to shipping

Source: www.hofstra.edu

Major Arctic Shipping Routes

PurposePurpose

Establish a limited track climatology of Establish a limited track climatology of intense arctic surface cyclonesintense arctic surface cyclones

Relate track climatology to large-scale Relate track climatology to large-scale arctic flowarctic flow

Examine cyclone mergersExamine cyclone mergers

Perform a brief case study of a cyclone Perform a brief case study of a cyclone merger eventmerger event

DatasetsDatasets

GFS 0.5° analysisGFS 0.5° analysis• Storm-track climatology and case studyStorm-track climatology and case study

NCEP–NCAR ReanalysisNCEP–NCAR Reanalysis• Large-scale mean/anomaly computationsLarge-scale mean/anomaly computations

CPC daily teleconnection indicesCPC daily teleconnection indices• 1 Jan 1950 – 30 Jun 20081 Jan 1950 – 30 Jun 2008

SourcesSources• UAlbany DEAS data archiveUAlbany DEAS data archive• ESRLESRL• CPCCPC

MethodologyMethodology DefinitionsDefinitions

• Cool season: 1 Oct – 31 MarCool season: 1 Oct – 31 Mar• Arctic: poleward of 50°NArctic: poleward of 50°N• Intense cyclone: central MSLP ≤ 980 hPa Intense cyclone: central MSLP ≤ 980 hPa

Manually analyzed surface mapsManually analyzed surface maps

• Genesis/lysis timeGenesis/lysis time• Position and trackPosition and track• Central pressureCentral pressure• Merger/nonmergerMerger/nonmerger

Use teleconnection indices Use teleconnection indices

• Arctic Oscillation (AO) and North Atlantic Oscillation (NAO)Arctic Oscillation (AO) and North Atlantic Oscillation (NAO)

Normalize CPC datasetsNormalize CPC datasets

• Obtain a mean (Obtain a mean (μμ) of 0 and a standard deviation () of 0 and a standard deviation (σσ) of 1 ) of 1 for each index datasetfor each index dataset

Large-scale Arctic Flow RepresentationLarge-scale Arctic Flow Representation

PhasePhase σσ Ranges Ranges PercentilesPercentiles

NegativeNegative < −0.43 < −0.43 σσ 0 to 33.33%0 to 33.33%

NeutralNeutral −−0.43 to 0.43 0.43 to 0.43 σσ 33.34 to 66.67%33.34 to 66.67%

PositivePositive > 0.43 > 0.43 σσ 66.68 to 100%66.68 to 100%

Define regimesDefine regimes

• AO/NAO must remain in the positive or negative phase for at AO/NAO must remain in the positive or negative phase for at least five consecutive days for a time period to qualify as a least five consecutive days for a time period to qualify as a positive or negative regimepositive or negative regime

• All other time periods qualify as neutral regimes All other time periods qualify as neutral regimes

Large-scale Arctic Flow RepresentationLarge-scale Arctic Flow Representation

2005–06 Cool-season AO/NAO Time Series2005–06 Cool-season AO/NAO Time Series

AO NAO

Red shading: positive regime

Blue shading: negative regime

2006–07 Cool-season AO/NAO Time Series2006–07 Cool-season AO/NAO Time Series

Red shading: positive regime

Blue shading: negative regime

AO NAO

2005–06 Cool-season 300 hPa 2005–06 Cool-season 300 hPa Height Anomaly and Wind SpeedHeight Anomaly and Wind Speed

Source: www.esrl.noaa.gov

CI = 2.5 m s−1

Wind Speed

CI = 10 m

Height Anomaly

μAO

μNAO

= −0.35= −0.22

Source: www.esrl.noaa.gov

Wind Speed

2006–07 Cool-season 300 hPa 2006–07 Cool-season 300 hPa Height Anomaly and Wind SpeedHeight Anomaly and Wind Speed

CI = 2.5 m s−1CI = 10 m

Height Anomaly

μAO

μNAO

= 0.52= 0.13

Large-scale Arctic Flow SummaryLarge-scale Arctic Flow Summary

2005–06 Cool Season2005–06 Cool Season• Mainly negative AO/NAO patternMainly negative AO/NAO pattern• Weakened polar jetWeakened polar jet

2006–07 Cool Season2006–07 Cool Season• Mainly positive AO/NAO patternMainly positive AO/NAO pattern• Strengthened polar jetStrengthened polar jet

2005–06 Cool-season Storm Tracks2005–06 Cool-season Storm Tracks

Oct–Nov

Dec–Jan

Feb–Mar

50 Storms• Oct–Nov: 20

• Dec–Jan: 21

• Feb–Mar: 9

2006–07 Cool-season Storm Tracks2006–07 Cool-season Storm Tracks

Oct–Nov

Dec–Jan

Feb–Mar

Case Study

95 Storms• Oct–Nov: 25

• Dec–Jan: 46

• Feb–Mar: 24

Cyclogenesis Events vs. AO/NAO Regime (2005–07)Cyclogenesis Events vs. AO/NAO Regime (2005–07)

Arctic more Arctic more active during neutral to positive AO/NAO regimes (strengthened polar jet)

Merger Locations by Month (2005–07)Merger Locations by Month (2005–07)Oct–Nov

Dec–Jan

Feb–Mar

Case Study

39 Mergers• Oct–Nov: 11

• Dec–Jan: 17

• Feb–Mar: 11

Arctic–Arctic Mergers

21

Arctic–Midlatitude Mergers

18

Merger Locations by Strength (2005–07)Merger Locations by Strength (2005–07)970–980 hPa

960–969 hPa

950–959 hPa

< 950 hPa

39 Mergers• 970–980 hPa: 15

• 960–969 hPa: 13

• 950–959 hPa: 9

• < 950 hPa: 2

Case Study

Arctic–Arctic Mergers

Arctic–Midlatitude Mergers

Case StudyCase Study

Example of an arctic–midlatitude cyclone merger Example of an arctic–midlatitude cyclone merger eventevent

Occurred over the North Atlantic southeast of Occurred over the North Atlantic southeast of Greenland during 7–11 Dec 2006Greenland during 7–11 Dec 2006

Two surface cyclones and three positive potential Two surface cyclones and three positive potential vorticity (PV) anomalies mergedvorticity (PV) anomalies merged

Surface Low Tracks and 500 hPa Mean HeightSurface Low Tracks and 500 hPa Mean Height

500 hPa mean height (dam) for 6–12 Dec 2006

MSLP Time SeriesMSLP Time Series

• Well-developed, rapidly strengthening midlatitude cyclone absorbs arctic cyclone

• System deepens 53 hPa in 24 h (1800 UTC 8 Dec – 1800 UTC 9 Dec)

• Merged cyclone reaches lowest MSLP value of 928 hPa on 1200 UTC 10 Dec

PV Anomaly Tracks PV Anomaly Tracks

• PV anomaly “A” breaks off high PV reservoir over Siberia (21 Nov)

• PV anomalies “C” and “D” break off high PV reservoir over North Pole (3–4 Dec)

• PV anomaly “B” breaks off PV anomaly “A” over Labrador Sea (6 Dec)

• PV anomalies “B,” “C,” and “D” merge over North Atlantic (10 Dec)

Surface Lows and PV AnomaliesSurface Lows and PV Anomalies

• PV anomaly “B” induces arctic cyclone on 0000 UTC 7 Dec

• PV anomaly “D” induces midlatitude cyclone on 0000 UTC 8 Dec

• PV anomaly “C” merges with “B” and “D,” helping merged cyclone intensify

1200 UTC 8 Dec 2006 Sounding for Upton, NY1200 UTC 8 Dec 2006 Sounding for Upton, NY

PV anomaly D

Dynamic Tropopause Height:

2630 m

QG Rossby Penetration Depth for PV anomaly “D”:

10320 m

0000 UTC 7 Dec 2006: 300 hPa Wind Speed (kt), 0000 UTC 7 Dec 2006: 300 hPa Wind Speed (kt),

1000–500 hPa Thickness (dam), MSLP (hPa)1000–500 hPa Thickness (dam), MSLP (hPa)

ConclusionsConclusions

145 intense arctic surface cyclones 145 intense arctic surface cyclones occurring over both cool seasons yielding occurring over both cool seasons yielding a frequency of 10–15 per montha frequency of 10–15 per month• High intraseasonal and interannual variabilityHigh intraseasonal and interannual variability

Arctic most active in neutral to positive Arctic most active in neutral to positive AO/NAO regimesAO/NAO regimes• Strengthened polar jet associated with higher Strengthened polar jet associated with higher

frequency of intense arctic stormsfrequency of intense arctic storms


Storms most frequent over Gulf of Storms most frequent over Gulf of Alaska/Aleutians and North Atlantic/East Alaska/Aleutians and North Atlantic/East Arctic OceansArctic Oceans• Clustering near end of well-known storm tracksClustering near end of well-known storm tracks

Atlantic more active than the PacificAtlantic more active than the Pacific• More storms tend to form farther north in the AtlanticMore storms tend to form farther north in the Atlantic


All mergers occur poleward of 50°NAll mergers occur poleward of 50°N• Storms stay or move into the arcticStorms stay or move into the arctic

Arctic–midlatitude mergers typically occur Arctic–midlatitude mergers typically occur when southern storm is well developedwhen southern storm is well developed• Arctic storm provides extra vorticity; expedites Arctic storm provides extra vorticity; expedites

vorticity growthvorticity growth

Further ResearchFurther Research

Use automated tracking program to include Use automated tracking program to include several more cool seasonsseveral more cool seasons

Other aspects of cyclones vs. regimesOther aspects of cyclones vs. regimes• IntensityIntensity• Mean locationMean location• Merger/nonmergerMerger/nonmerger

Merger BehaviorMerger Behavior• Strongest mergers southeast of GreenlandStrongest mergers southeast of Greenland• Arctic–arctic vs. arctic–midlatitude mergersArctic–arctic vs. arctic–midlatitude mergers

Questions/Comments?Questions/Comments?

intense surface cyclone activity in the arctic during the 2005 – 06 and 2006 – 07 cool seasons

Documents

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hpa960969 hpa950959

cool seasonsbrian silviotti

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