May 16 th 2011 US EAST COAST WINTER STORM VARIABILITY DUE TO NAO AND OTHER LOWFREQUENCY OSCILLATIONS By Brandon Meitz May 16 th 2011 L Outline What is winter storm variability What are ECWS ID: 407676
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Slide1
By Brandon MeitzMay 16th, 2011
U.S.
EAST COAST WINTER STORM VARIABILITY DUE TO NAO AND OTHER LOW-FREQUENCY OSCILLATIONSSlide2
By Brandon MeitzMay 16th, 2011
L
Outline
What is winter storm variability?
What are ECWS?
What is the NAO?How does ENSO affect ECWS?PNA and ECWSAtlantic SST’s and storm trackingConcluding remarks
U.S.
EAST COAST WINTER STORM VARIABILITY DUE TO NAO AND OTHER LOW-FREQUENCY OSCILLATIONSSlide3
Winter Storm Variability
Winter storm variability
The modification of large scale atmospheric circulations that influence storm system properties in the Northeastern United States every winter.
Trough axis location variability
This affects storm tracks as well as the number of storms experienced
Eastward shift typical of Mid-Atlantic snow anomalies
Trough intensity variability
This affects intensity of storms and temperature advection that can occur along the Northeastern U.S.
Deepening of trough indicative of below average temps for Northeast U.S.Slide4
What are ECWS?
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East Coast Winter Storms:
Mid-latitude cyclones of extra tropical origin that can form during December-March off the Atlantic Coastline of the Eastern United States as well as inland locations.
Their distribution and tracking patterns are dependent on large scale atmospheric circulation.
Example: Nor’easters
Strong steady winds blowing out of the northeasterly direction
Storms are accompanied with rain, snow, high energy waves, and storm surge
Winds can exceed hurricane forceSlide5
What is the Northern Atlantic Oscillation?
Redistribution of atmospheric mass along dipole Icelandic Low and Azores High
Positive phase (+) associated with relatively zonal flow across eastern U.S.
Negative phase (-) associated with meridional displacement of polar front
Variability of large scale circulation also affects SST distribution
Negative (-) NAO conditions allow encroachment of Labrador current, and southward shift of Gulf StreamStorm tracks tend to follow Gulf Stream out to sea, missing New EnglandSlide6
What is the Northern Atlantic Oscillation?
Variability of large scale circulation also affects SST distribution
Negative (-) NAO conditions allow encroachment of Labrador current, and southward shift of Gulf Stream
Storm tracks tend to follow Gulf Stream out to sea, missing New England
Redistribution of atmospheric mass along dipole Icelandic Low and Azores High
Positive phase (+) associated with relatively zonal flow across eastern U.S.
Negative phase (-) associated with meridional displacement of polar frontSlide7
How does ENSO affect ECWS?
El Nino/La Nina-Southern Oscillation
The anomalous warming and cooling of equatorial Pacific Ocean temps has a teleconnection with the Atlantic Winter Storm season
During El Nino phases, cyclogenesis increases in the Gulf of Mexico/Eastern Seaboard, and decreases across Canadian Shield
La Nina phases lead to fewer coastal storms and more continental storms that affect inland New England locations
Global teleconnections of ENSOIncreased precipitation and warmer temps are experienced across Northeast as a result of El Nino phase.Slide8
Why was 2009-2010 so active? Slide9
PNA and ECWS
Pacific/North American Oscillation
Positive PNA has same meridional affects to large scale flow as the negative NAO phase
PNA could act to amplify or dampen effects of NAO and other oscillations that govern East Coast Storms
Overlaid NAO index (black) over PNA index
When phases opposite of each other, amplification
of meridional flow occurs
In phase index values are of opposite flow regimes (dampening)Slide10
Atlantic SST’s and storm tracking
Atlantic SST’s and storm tracking
Atmospheric Oscillations tend to influence SST’s
Meridional flows displace warm Gulf Stream Currents southwards
Zonal patterns allow northern encroachment of warm Gulf Stream currents
Atmo-Ocean-Atmo
feedback seems to occur
If Gulf Stream is displaced southwards and diverts away from continent, storms also tend to veer away from land.
Wind stress is greater during positive NAO
Zonal winds stronger than meridional meandering during negative NAO phaseSlide11
Concluding remarks
Winter climate variables are many…
Trough axis and intensity off East Coast is responsible for source and intensity of storms that affect the Mid-Atlantic and Northeastern United States.
Zonal conditions lead to warmer weather across Northeast and Mid-Atlantic with Alberta Clipper systems passing through region via Great Lakes.
Meridional dip of polar front leads to cold air breakouts in Mid-Atlantic with increases in precipitation and snowfall, whereas New England can experience drought conditions.
NAO, ENSO, PNA oscillations modify large scale circulation of region leading to either zonal or meridional flow patterns. Ocean-Atmosphere influences are still under investigation, however, with a warming climate, changes in weather patterns can be suspected to occurSlide12
References
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