cool-season high winds in the northeast u.s. jonas v. asuma, lance f. bosart, daniel keyser...
TRANSCRIPT
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Cool-Season High Winds in the Northeast U.S.
Jonas V. Asuma, Lance F. Bosart, Daniel Keyser
Department of Atmospheric and Environmental Sciences
University at Albany/SUNY
John S. Quinlan, Thomas A. Wasula, Hugh W. Johnson, Kevin S. Lipton
NOAA/NWS, Albany, NY
NROW XI Albany, NY5 November 2009
NOAA/CSTAR Grant NA07NWS4680001
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Overview
• Motivation– Cool-season high wind events can be damaging
and in some cases challenging to forecast– Structure and environment of such events needs
to be rigorously investigated• Objectives
– Provide climatological basis for forecasting– Compare large-scale patterns that typify event
types– Contrast convective potential of the environment
for event types
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Outline
• Data• Methodology• Results of Climatology• Results of Compositing• Conclusions
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Data
• Climatology– NCDC Thunderstorm and High Wind reports
• Composites– NCEP/NCAR 2.5° Reanalysis data
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• Climatology– Temporal Domain: 15 Oct 1993 through 31 Dec
2008– High Wind Definition: Wind measured ≥ 25 m s−1
or damaging winds of any magnitude– Event Definition: Any series of ≥ 2 reports
separated by 12 h before and after initial and final report
• Events defined by type:– Pure Gradient (PG): No thunderstorm wind reports– Pure Convective (PC): No gradient wind reports– Hybrid (HY): Both thunderstorm and gradient wind reports
Methodology (1 of 4)
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• Climatology– Spatial Domain: Greater Northeast– 575 total events
• 187 HY events• 223 PG events• 165 PC events
Methodology (2 of 4)
Reports
0.5° Barnes Analysis of spatial distribution of All wind reports
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• Composite– Spatial Domain: Northeast (NE)– 358 total events
• 158 HY events• 156 PG events• 44 PC events
Methodology (3 of 4)
0.5° Barnes Analysis of spatial distribution of All wind reports
Reports
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Methodology (4 of 4)
• Composite– Composite time (t = 0): Determined to be hour
(00, 06, 12, or 18 Z) closest to initial NE report• For reports at 03, 09, 15, or 21 Z earlier hour chosen• Events composited by event type
– Created report-relative composites• Grids shifted to location of initial Northeast report• Composites centered on centroid of initial Northeast
reports for each event type
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Climatology: Monthly Frequency
Oct Nov Dec Jan Feb Mar Apr0
10
20
30
40
50
60
70
80
Hybrid Pure Gradient Pure Convective
Ev
en
ts
N = 575
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Climatology: Annual Frequency
1994–1995
1995–1996
1996–1997
1997–1998
1998–1999
1999–2000
2000–2001
2001–2002
2002–2003
2003–2004
2004–2005
2005–2006
2006–2007
2007–20080
10
20
30
40
50
60
Hybrid Pure GradientPure Convective Total
Ev
en
ts
N = 575
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• Events per cool season:– PG: most events– PC: least events
• Annual variability:– PG: largest variability– HY: least variability
N = 14 years
Hybrid
Pure G
radie
nt
Pure C
onvective
0
5
10
15
20
25
Mean
Outliers
Ev
en
tsClimatology: Annual Variability
Whiskers encompass inner 90% of data
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Climatology: Event Variability
N = 27,644
N = 575
2–2525–50
50–7575–100
100–150
150–200
200–300
300–400
400–500
500–6000
20
40
60
80
100
120
140
160
Hybrid
Pure Gradient
Pure Convective
Reports
Ev
en
ts
N = 575
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• PC and PG events tied to seasonal cycle of convection– Dynamically vs. thermodynamically driven
• HY events have largest impact (more reports per event)– Max in Apr but not uncommon in other months– Likely dynamically AND thermodynamically driven
• Interseasonal variability possibly associated with seasonally averaged storm track
Summary of Climatology
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Composite Analyses: Surface
Composite initial NE report (star); MSLP (every 2 hPa, black);precipitable water (mm, shaded); 1000-hPa θ (every 4 K, red), total wind (≥10 kt, barbs)
(mm)
276 K
Pure Convective N = 44
L
H
H
Pure Gradient N = 156
H
LL
H
N = 158Hybrid
H
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Composite Analyses: 850 hPa
Composite initial NE report (star); 850-hPa Z (every 30 m, black), temperature (every 4°C, dashed);1000–850-hPa lapse rate (K km−1, shaded), wind shear (≥15 kt, barbs)
(K km−1)
0°C
Hybrid N = 158 Pure Gradient N = 156
Pure Convective N = 44
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Composite Analyses: 500 hPa
Composite initial NE report (star); 500-hPa Z (every 6 dam, black), lifted index (K, shaded); 1000–500-hPa thickness (every 6 dam, red) and wind shear (≥ 40 kts, barbs)
(K)
540 dam
Pure Convective N = 44
Pure Gradient N = 156Hybrid N = 158
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Composite Analyses: 300 hPa
Composite initial NE report (star); 300-hPa Z (every 10 dam, black), total wind speed (m s−1, shaded); mslp (every 2 hPa below 1014 hPa only, dashed);jet max (J) and surface low (L) labeled
N = 156Pure Gradient
Pure Convective N = 44
(m s−1)
Hybrid N = 158
L
L
LJ
J
J
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• HY and PC cyclones located north of initial report; PG cyclone located east of initial report
• PC events tend to be most moist, least stable – PG events tend to be least moist, most stable
• HY and PG upper-level wave patterns more amplified compared to PC composite– Suggests stronger dynamical processes
• HY report occurs in warm sector in advance of cold front– PG report occurs in region of cold air advection– PC report occurs on warm side of zonally oriented
baroclinic zone
• Jet structures vary by event type
Composite Summary
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• HY events associated with favorable dynamic AND thermodynamic environments– PG events maximize in Dec: dynamically driven– PC events maximize in Apr: thermodynamically driven
• Interseasonal variability likely due to variations in storm track– HY event: cyclone track north of domain– PG event: cyclone track east of domain
Conclusions
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Extra Images
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Climatology: Frequency of Reports
Oct Nov Dec Jan Feb Mar Apr0
50010001500200025003000350040004500
Monthly Frequency
Gradient Tstorm
Repo
rts
N = 28,872
94–9596–97
98–9900–01
02–0304–05
06–070
500
1000
1500
2000
2500
3000
3500
Yearly Frequency
Gradient Tstorm
Repo
rts
N = 27,644
0 to 33 to 6
6 to 99 to 12
12 to 1515 to 18
18 to 2121 to 24
0500
1000150020002500300035004000
Diurnal Frequency
Gradient Tstorm
Repo
rts
N = 28,872
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Climatology: Frequency of ReportsPopulation N = 27,751
0.5° Barnes Analysis of spatial distribution of Population
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Climatology: Frequency of ReportsPopulation N = 27,751
0.5° Barnes Analysis of spatial distribution of Population
Major Population area
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Climatology: Frequency of Reports
0.5° Barnes Analysis of spatial distribution of All wind reports
All N = 28,540
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Climatology: Frequency of Reports
0.5° Barnes Analysis of spatial distribution of All wind reports
All N = 28,540
Major Population area
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Gradient
Thunderstorm
Population
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Climatology: Frequency of ReportsGradient N = 16,907
0.5° Barnes Analysis of spatial distribution of Gradient wind reports
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Climatology: Frequency of ReportsGradient N = 16,907
0.5° Barnes Analysis of spatial distribution of Gradient wind reports
Major Population area
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Climatology: Frequency of ReportsThunderstorm N = 11,633
0.5° Barnes Analysis of spatial distribution of Thunderstorm wind reports
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Climatology: Frequency of ReportsThunderstorm N = 16,907
Major Population area
0.5° Barnes Analysis of spatial distribution of Thunderstorm wind reports