Intense Surface Cyclone Activity in the Arctic during the 200506 and 200607 Cool Seasons

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Intense Surface Cyclone Activity in the Arctic
during the 200506 and 200607 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-0434189
• 10th Northeast Regional Operational Workshop
• 5 November 2008

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Motivation
Major Arctic Shipping Routes

• Arctic cyclones not extensively studied
• Intense arctic cyclones
• pose economic hazards,
• especially to shipping

Source www.hofstra.edu
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Purpose

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

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Datasets

• GFS 0.5 analysis
• Storm-track climatology and case study
• NCEPNCAR Reanalysis
• Large-scale mean/anomaly computations
• CPC daily teleconnection indices
• 1 Jan 1950 30 Jun 2008
• Sources
• UAlbany DEAS data archive
• ESRL
• CPC

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Methodology

• Definitions
• Cool season 1 Oct 31 Mar
• Arctic poleward of 50N
• Intense cyclone central MSLP 980 hPa
• Manually analyzed surface maps
• Genesis/lysis time
• Position and track
• Central pressure
• Merger/nonmerger

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Large-scale Arctic Flow Representation

• Use teleconnection indices
• Arctic Oscillation (AO) and North Atlantic
  Oscillation (NAO)
• Normalize CPC datasets
• Obtain a mean (µ) of 0 and a standard deviation
  (s) of 1 for each index dataset

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Large-scale Arctic Flow Representation

• 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
  regime
• All other time periods qualify as neutral regimes
  

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200506 Cool-season AO/NAO Time Series
AO
NAO
Red shading positive regime Blue shading
negative regime
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200607 Cool-season AO/NAO Time Series
AO
NAO
Red shading positive regime Blue shading
negative regime
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200506 Cool-season 300 hPa Height Anomaly and
Wind Speed
Wind Speed
Height Anomaly
CI 2.5 m s-1
CI 10 m
µAO
-0.35
Source www.esrl.noaa.gov
µNAO
-0.22
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200607 Cool-season 300 hPa Height Anomaly and
Wind Speed
Wind Speed
Height Anomaly
CI 2.5 m s-1
CI 10 m
µAO
0.52
Source www.esrl.noaa.gov
µNAO
0.13
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Large-scale Arctic Flow Summary

• 200506 Cool Season
• Mainly negative AO/NAO pattern
• Weakened polar jet
• 200607 Cool Season
• Mainly positive AO/NAO pattern
• Strengthened polar jet

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200506 Cool-season Storm Tracks
OctNov DecJan FebMar

• 50 Storms
• OctNov 20
• DecJan 21
• FebMar 9

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200607 Cool-season Storm Tracks
OctNov DecJan FebMar Case Study

• 95 Storms
• OctNov 25
• DecJan 46
• FebMar 24

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Cyclogenesis Events vs. AO/NAO Regime (200507)

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

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Merger Locations by Month (200507)
OctNov DecJan FebMar Case Study

• 39 Mergers
• OctNov 11
• DecJan 17
• FebMar 11

ArcticArctic Mergers 21 ArcticMidlatitu
de Mergers 18
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Merger Locations by Strength (200507)
970980 hPa 960969 hPa 950959 hPa lt 950 hPa
Case Study

• 39 Mergers
• 970980 hPa 15
• 960969 hPa 13
• 950959 hPa 9
• lt 950 hPa 2

ArcticArctic Mergers ArcticMidlatitude
Mergers
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Case Study

• Example of an arcticmidlatitude cyclone merger
  event
• Occurred over the North Atlantic southeast of
  Greenland during 711 Dec 2006
• Two surface cyclones and three positive potential
  vorticity (PV) anomalies merged

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Surface Low Tracks and 500 hPa Mean Height
500 hPa mean height (dam) for 612 Dec 2006
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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

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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 (34 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)

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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

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1200 UTC 8 Dec 2006 Sounding for Upton, NY
Dynamic Tropopause Height 2630 m QG Rossby
Penetration Depth for PV anomaly D 10320 m
PV anomaly D
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0000 UTC 7 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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1200 UTC 7 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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0000 UTC 8 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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1200 UTC 8 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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0000 UTC 9 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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1200 UTC 9 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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0000 UTC 10 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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1200 UTC 10 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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0000 UTC 11 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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1200 UTC 11 Dec 2006 300 hPa Wind Speed (kt),
1000500 hPa Thickness (dam), MSLP (hPa)
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Conclusions

• 145 intense arctic surface cyclones occurring
  over both cool seasons yielding a frequency of
  1015 per month
• High intraseasonal and interannual variability
• Arctic most active in neutral to positive AO/NAO
  regimes
• Strengthened polar jet associated with higher
  frequency of intense arctic storms

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Conclusions

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

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Conclusions

• All mergers occur poleward of 50N
• Storms stay or move into the arctic
• Arcticmidlatitude mergers typically occur when
  southern storm is well developed
• Arctic storm provides extra vorticity expedites
  vorticity growth

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Further Research

• Use automated tracking program to include several
  more cool seasons
• Other aspects of cyclones vs. regimes
• Intensity
• Mean location
• Merger/nonmerger
• Merger Behavior
• Strongest mergers southeast of Greenland
• Arcticarctic vs. arcticmidlatitude mergers

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Questions/Comments?