Arctic Cyclone Activity and its Relationship with Large-scale Climate Leading Mode

It is well documented that pressure is lower in the central Arctic when the Arctic Oscillation (AO) or the North Atlantic Oscillation (NAO) is in its positive phase than when the AO (NAO) is in its negative phase. However, it is unknown whether this lower pressure is primarily the result of (1) more frequent cyclones, (2) deeper cyclones, (3) more persistent cyclones, or some combination of (1)-(3). If either of the first two alternatives predominates, the regional origins and trajectories of the cyclonic activity are unknown. These issues have direct relevance to the Arctic climate system in several respects from atmosphere to sea-ice and ocean. In this study, we determine the nature of the pressure reduction over the Arctic Ocean during the positive phase of the AO by compiling statistics of cyclone frequency and intensity during the two phases of the AO. The cyclone statistics are obtained by identifying each cyclone in the region poleward of 70ºN with the 6-hourly NCAR/NCEP reanalysis from 1948 to present, which shows remarkable interannual variability for the cyclones either locally born in the Arctic or originated from lower latitudes.