Intense Surface Cyclone Activity in the Arctic during the 2005–06 and 2006–07 Cool Seasons Brian Silviotti, Lance F. Bosart, and Daniel Keyser Department of Earth and Atmospheric Sciences University at Albany, Albany, New York NSF Grant ATM th Northeast Regional Operational Workshop 5 November 2008

Motivation Arctic cyclones not extensively studied Arctic cyclones not extensively studied Intense arctic cyclones Intense arctic cyclones pose economic hazards, pose economic hazards, especially to shipping especially to shipping Source: Major Arctic Shipping Routes

Purpose Establish a limited track climatology of intense arctic surface cyclones Establish a limited track climatology of intense arctic surface cyclones Relate track climatology to large-scale arctic flow Relate track climatology to large-scale arctic flow Examine cyclone mergers Examine cyclone mergers Perform a brief case study of a cyclone merger event Perform a brief case study of a cyclone merger event

Datasets GFS 0.5° analysis GFS 0.5° analysis Storm-track climatology and case studyStorm-track climatology and case study NCEP–NCAR Reanalysis NCEP–NCAR Reanalysis Large-scale mean/anomaly computationsLarge-scale mean/anomaly computations CPC daily teleconnection indices CPC daily teleconnection indices 1 Jan 1950 – 30 Jun Jan 1950 – 30 Jun 2008 Sources Sources UAlbany DEAS data archiveUAlbany DEAS data archive ESRLESRL CPCCPC

Methodology Definitions Definitions 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 hPaIntense cyclone: central MSLP ≤ 980 hPa Manually analyzed surface maps Manually 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 datasets Normalize CPC datasets Obtain a mean (μ) of 0 and a standard deviation (σ) of 1 for each index datasetObtain a mean (μ) of 0 and a standard deviation (σ) of 1 for each index dataset Large-scale Arctic Flow Representation

Phase σ Ranges Percentiles Negative < −0.43 σ 0 to 33.33% Neutral −0.43 to 0.43 σ to 66.67% Positive > 0.43 σ to 100% Define regimes Define regimes AO/NAO must remain in the positive or negative phase for at least five consecutive days for a time period to qualify as a positive or negative regimeAO/NAO must remain in the positive or negative phase for at least five consecutive days for a time period to qualify as a positive or negative regime All other time periods qualify as neutral regimesAll other time periods qualify as neutral regimes Large-scale Arctic Flow Representation

2005–06 Cool-season AO/NAO Time Series AO NAO Red shading: positive regime Blue shading: negative regime

2006–07 Cool-season AO/NAO Time Series Red shading: positive regime Blue shading: negative regime AO NAO

2005–06 Cool-season 300 hPa Height Anomaly and Wind Speed Source: CI = 2.5 m s −1 Wind Speed CI = 10 m Height Anomaly μ AO μ NAO = −0.35 = −0.22

Source: Wind Speed 2006–07 Cool-season 300 hPa Height Anomaly and Wind Speed CI = 2.5 m s −1 CI = 10 m Height Anomaly μ AO μ NAO = 0.52 = 0.13

Large-scale Arctic Flow Summary 2005–06 Cool Season 2005–06 Cool Season Mainly negative AO/NAO patternMainly negative AO/NAO pattern Weakened polar jetWeakened polar jet 2006–07 Cool Season 2006–07 Cool Season Mainly positive AO/NAO patternMainly positive AO/NAO pattern Strengthened polar jetStrengthened polar jet

2005–06 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 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) Arctic more Arctic more active during neutral to positive AO/NAO regimes (strengthened polar jet)

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) 970–980 hPa 960–969 hPa 950–959 hPa < 950 hPa 39 Mergers 970–980 hPa: –969 hPa: –959 hPa: 9 < 950 hPa: 2 Case Study Arctic–Arctic Mergers Arctic–Midlatitude Mergers

Case Study Example of an arctic–midlatitude cyclone merger event Example of an arctic–midlatitude cyclone merger event Occurred over the North Atlantic southeast of Greenland during 7–11 Dec 2006 Occurred over the North Atlantic southeast of Greenland during 7–11 Dec 2006 Two surface cyclones and three positive potential vorticity (PV) anomalies merged Two surface cyclones and three positive potential vorticity (PV) anomalies merged

Surface Low Tracks and 500 hPa Mean Height 500 hPa mean height (dam) for 6–12 Dec 2006

MSLP 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 “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 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, NY PV anomaly D Dynamic Tropopause Height: 2630 m QG Rossby Penetration Depth for PV anomaly “D”: m

0000 UTC 7 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

1200 UTC 7 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

0000 UTC 8 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

1200 UTC 8 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

0000 UTC 9 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

1200 UTC 9 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

0000 UTC 10 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

1200 UTC 10 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

0000 UTC 11 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

1200 UTC 11 Dec 2006: 300 hPa Wind Speed (kt), 1000–500 hPa Thickness (dam), MSLP (hPa)

Conclusions 145 intense arctic surface cyclones occurring over both cool seasons yielding a frequency of 10–15 per month 145 intense arctic surface cyclones occurring over both cool seasons yielding a frequency of 10–15 per month High intraseasonal and interannual variabilityHigh intraseasonal and interannual variability Arctic most active in neutral to positive AO/NAO regimes Arctic most active in neutral to positive AO/NAO regimes Strengthened polar jet associated with higher frequency of intense arctic stormsStrengthened polar jet associated with higher frequency of intense arctic storms

Conclusions Storms most frequent over Gulf of Alaska/Aleutians and North Atlantic/East Arctic Oceans Storms most frequent over Gulf of Alaska/Aleutians and North Atlantic/East Arctic Oceans Clustering near end of well-known storm tracksClustering near end of well-known storm tracks Atlantic more active than the Pacific Atlantic more active than the Pacific More storms tend to form farther north in the AtlanticMore storms tend to form farther north in the Atlantic

Conclusions All mergers occur poleward of 50°N All mergers occur poleward of 50°N Storms stay or move into the arcticStorms stay or move into the arctic Arctic–midlatitude mergers typically occur when southern storm is well developed Arctic–midlatitude mergers typically occur when southern storm is well developed Arctic storm provides extra vorticity; expedites vorticity growthArctic storm provides extra vorticity; expedites vorticity growth

Further Research Use automated tracking program to include several more cool seasons Use automated tracking program to include several more cool seasons Other aspects of cyclones vs. regimes Other aspects of cyclones vs. regimes IntensityIntensity Mean locationMean location Merger/nonmergerMerger/nonmerger Merger Behavior Merger Behavior Strongest mergers southeast of GreenlandStrongest mergers southeast of Greenland Arctic–arctic vs. arctic–midlatitude mergersArctic–arctic vs. arctic–midlatitude mergers

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