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					An Investigation of Cold-Air
Cyclogenesis Along the East Coast
of the United States
Christopher Warren
Graduate Student
Plymouth State University

NROW 9

November 7th, 2007
Types of East Coast Winter Storms


                     • 4 classifications of East Coast
                       cyclogenesis defined by Gurka
                       et al. (1995).
                     • Coastal events are;
                       ▫ Miller Type B
                       ▫ Zipper Lows
                       ▫ Cold-air Cyclogenesis
Cold-Air Cyclogenesis
• Anderson et al. (1969) defines cold air cyclones as
  cyclonic disturbances that form over the ocean behind a
  polar front.
  ▫ Evolves into a comma-shape pattern
  ▫ Cold air comma cloud is downstream of an upper-tropospheric
    vorticity maximum.

• Cold-air cyclogenesis is most frequent in the N. Atlantic,
  N. Pacific, and over the N. American continent (Weber and
  Wilderotter 1982)


• Cold-air cyclogenesis relative to 1000-500 hPa thickness
  ribbon (Businger and Reed 1989, Gurka et al. 1995, Businger et al. 2003)
Previous Research of East Coast Cold-air Cyclogenesis

                                     • Case study by Rosenblum and
                                       Sanders (1974)
                                     • 18 December 1971
                                     • Unusually cold air indicted by
                                       1000-500 mb thickness.


                                             Visible satellite image at 1800 UTC 24 Feb. 1989.

   Figure taken from Rosenblum and
   Sanders (1974)

     • Gurka et al. (1995) and Businger
       et al. (2003) discussed how a
       small synoptic-scale cyclone
       formed during a cold-air
       outbreak.
     • 24 February 1989
     • Formed in cold air region relative
       to 1000-500 mb thickness.
Objectives
1. Determine how frequently cold-air cyclones relative to the 1000-
   500 hPa thickness ribbon occur.
2. Examine conditions that are favorable for their development.
3. Find similarities or differences between these storms and other
   East Coast cyclones.


To do this a 9-yr climatology using a multi-
 variable approach will be used to hopefully
 improve forecaster awareness when the
 conditions are ripe for East Coast cold-air
 cyclogenesis.
 Cyclone Identification
• 9-year period from 1997-2006
   ▫ Cool Season Months (1 Oct – 30 Apr)


• Data: North American Regional
  Reanalysis (NARR)

• East Coast Winter Storm (ECWS)
  region for cyclone development and
  intensification modified from
  Hirsch et al. (2001)

• Cyclone events were counted when
  any part of a central closed sea-        ECWS Region
  level pressure isobar (interval of 2
  hPa) was present in the ECWS
  region.
Determining Cold-Air Cyclogenesis Events
• Cyclogenesis was determined to
  have occurred when the sea-level
  pressure in the center of
  circulation decreased by at least 2
  hPa/6-hr period
  ▫ At least 2 periods but not
    necessarily consecutive in 24 hrs

• Events were classified as cold-air
  when daily 1000-500 hPa
  thickness values near the center
  of low pressure were below -0.5
  standard deviations from a 32-yr
  daily mean.
  ▫ Thickness data from NCEP/NCAR
    Reanalysis Dataset
  ▫ Received from Anantha Aiyyer (NC.
    State)
ECWS Climatology Results

                           •512 total cyclones
                           •Avg = 57 per season




                           •259 cyclogenesis;
                           •Avg = 29 per season




                           •20 cold-air cyclones
Cyclone Locations & Tracks
Composite Comparison Methods

• Generated composites using;
  ▫ 20 cold-air cyclones
  ▫ 43 non cold-air cyclones from the 2000-01 cool
    season.
• Data: NARR
• Composites generated for each of the three sub-
  regions using IDV.
North Sub-Region: 300 hPa Level
          24-hrs prior to initial cyclogenesis (t = -24 hr)

Cold-air Composite                         Non Cold-air Composite




           Isoheights (black solid lines), wind speeds (color-fill contours)
North Sub-Region: 300 hPa Level
          12-hrs prior to initial cyclogenesis (t = -12 hr)

Cold-air Composite                         Non Cold-air Composite




           Isoheights (black solid lines), wind speeds (color-fill contours)
North Sub-Region: 300 hPa Level
              Time of initial cyclogenesis (t = 0 hr)

Cold-air Composite                         Non Cold-air Composite




           Isoheights (black solid lines), wind speeds (color-fill contours)
North Sub-Region: 500 hPa Level
                                 (t = -12 hr)

Cold-air Composite                         Non Cold-air Composite




           Isoheights (black solid lines), temperature(color-fill contours)
North Sub-Region: 500 hPa Level
                                  (t = 0 hr)

Cold-air Composite                         Non Cold-air Composite




           Isoheights (black solid lines), temperature(color-fill contours)
North Sub-Region: Surface
                                         (t = 0 hr)

Cold-air Composite                                Non Cold-air Composite
     Isobars (black solid lines), 2 m temperature(color-fill contours), wind barbs (m/s)




**Note: Due to time constraints composites from East and West sub-regions were left out.
Case Study
• Focused on atmospheric conditions 24-hr prior to 24-hrs following
  cyclogenesis event.




• 21-22 February 1999
  ▫ Location: East Sub-Region
  ▫ Reason: Cyclogenesis
    occurred when thickness
    was below -1.0 standard
    deviations.
East Region: 700 hPa Level


T = -12 hr                                   T = 0 hr




             Isoheights (black solid lines), temperature(color-fill contours)
East Region: Surface


T = -12 hr                                      T = 0 hr




             Isobars (black solid lines), 2 m temperature(color-fill contours)
Conclusions
• 20 cold-air cyclones identified off East Coast of U.S. during cool season
  months from 1997-2006.
   ▫ On average expect to see about 2.2 cold-air cyclones per year.


• Cold-air composites have colder temperatures and lower heights above 850
  hPa with greatest differences seen in North Sub-Region composites from
  non cold-air composites.
   ▫ Forecasting potential


• Case studies show that the dynamical processes in cold-air cyclogenesis are
  similar to that of other extratropical East Coast midlatitude cyclones.

• Future research should focus on mesoscale processes and air-sea
  interactions for East Coast cold-air cyclones.
Questions & Comments
Special thanks to:

•Dr. Eric Hoffman (Advisor)
•Dr. Anantha Aiyyer
•Brendon Hoch

				
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