Large-scale atmospheric circulation patterns during polar low events over the Nordic seas

Abstract

The large-scale atmospheric circulation during polar low events over the Nordic seas (the North Atlantic between Greenland and Novaya Zemlya) is investigated on the basis of a recently compiled data set that was derived purely from satellite observations. A classification system is applied that divides the polar lows into four types (western polar lows, eastern polar lows, Greenland lee polar lows, and storm track polar lows). Type-specific large-scale atmospheric circulation patterns are identified from National Centers for Environmental Prediction reanalysis data. These are distinct in sea level pressure, upper level geopotential height, and the difference between the skin temperature of the ocean and upper level temperature. Eastern polar lows are found to be associated with a strong blocking situation caused by anomalously high pressure over Iceland and a synoptic-scale low-pressure anomaly over the Barents Sea. A weaker blocking situation with an anomalous ridge over Greenland reaching into the Inninger Sea and a low-pressure anomaly over the Norwegian Sea favors the development of western polar lows. Typical values for, polar low genesis are a geopotential height of 5030 geopotential meters at 500 hPa and a difference of 48 K between the skin temperature of the ocean and the temperature at 500 hPa. The locations of upper level low-pressure anomalies relative to the locations of the related anomalies at the sea level show that western and eastern polar lows form, on average, in a much less baroclinic large-scale environment than Greenland lee and storm track polar lows. Copyright 2009 by the American Geophysical Union.