Mesocyclone activity over the Northeast Atlantic. Part 2: An investigation of causal mechanisms

Causal mechanisms of mesocyclone and synoptic cyclone characteristics over the Northeast Atlantic and Nordic Seas are investigated using a 2-year database compiled from infrared satellite imagery. A strong seasonality is found, with peak activity in winter and a minimum in spring. A distinct interannual variability is also found. Smaller mesocyclones (<400 km diameter) were found to be strongly linked to the shallow baroclinic zone along the sea ice edge. Midsize mesocyclones, 200–600 km diameter, are often associated with cold air outbreaks following the passage of synoptic systems. A chart analysis confirms this, showing that convective instability is the major mechanism for the origin of these storms. Although the temporal coverage of the database is short, some support for this is found in comparison with teleconnection patterns and also potential reasons for the large interannual variability.