Marine cold-air outbreaks in the North Atlantic: temporal distribution and associations with large-scale atmospheric circulation
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The spatial and temporal distributions of marine cold air outbreaks (MCAOs) over the northern North Atlantic have been investigated using re-analysis data for the period from 1958 to 2007. MCAOs are large-scale outbreaks of cold air over a relatively warm ocean surface. Such conditions are known to increase the severity of particular types of hazardous mesoscale weather phenomena. We used a simple index for identifying MCAOs: the vertical potential temperature gradient between the sea surface and 700 hPa. It was found that atmospheric temperature variability is considerably more important than the sea surface temperature variability in governing both the seasonal and the inter-annual variability of MCAOs. Furthermore, a composite analysis revealed that a few well-defined and robust synoptic patterns are evident during MCAOs in winter. Over the Labrador and Irminger Seas the MCAO index was found to have a correlation of 0.70 with the North Atlantic Oscillation index, while over the Barents Sea a negative correlation of 0.42 was found.
KeywordsCold air outbreak Polar low Arctic Meteorology NAO Climatology Climate Extreme weather Severe weather
This is publication no. XXXX from the Bjerknes Center for Climate Research. Erik Kolstad’s work was supported by the Norwegian Research Council through its International Polar Year programme and the project IPY-THORPEX (grant no. 175992/S30). The NAO Index Data were provided by the Climate Analysis Section, NCAR, Boulder, USA (Hurrell 1995). The NCEP/NCAR re-analysis data were provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their web site at http://www.cdc.noaa.gov.
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