Date post: | 19-Dec-2015 |
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Precipitation Associated with 500 hPa Closed Cyclones
Anantha Aiyyer
Eyad Atallah
Department of Earth and Atmospheric Sciences, University at Albany
Motivation
• What percentage of precipitation in the Northeast is associated with closed lows?
• What are the regional and seasonal precipitation signals?
• Availability of gridded data sets.
Data and Methodology
• NCEP/NCAR Reanalyses at 500 hPa. • Unified Precipitation Dataset – .250 lat-lon
grid (http://www.cdc.noaa.gov/cdc/data.unified.html).
• Period of interest 1950-1998.• Use an objective algorithm to identify
closed lows.• Define a closed low as a 30 m height rise
from a local min in the height field.
• Mainly zonal distribution of closed lows.
• Genesis area in the NW Atlantic.
• Spring is the most active season.
• Summer is the least active season.
• Possible tropical cyclone contribution in the summer.
• Annual mean precipitation field strongly modulated by topography.
• Upslope and lake effect signatures dominate cool season precip.
• Terrain elevation signatures dominate warm season precip.
• Lows contribute a higher percentage of total precipitation in coastal areas, especially in Spring.
• Heaviest precip from lows in western quadrants.
• Upslope signatures strongest in western quadrants.
• Precip rates maximized with lows in SW quadrant.
• NE quadrant shows prominent lake effect signature.
• SE quadrant precip rates maximized along eastern most terrain features.
• Probability of occurrence decreases rapidly with increasing precip rates.
• 60% of lows produce mean precip rates of 5 mm or greater over the entire domain.
• Local maximum precipitation has a relatively even distribution over wide range of rates.
• Ideal low position for highest domain-wide precip is west of the NE.
• Ideal low position for highest local max precip is southwest of the NE.
Speed vs. Mean Precip
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Speed vs. Max Precip
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