Explosive cyclones in the North AtlanticNao influence and multidecadal variability

Abstract

In this study we have analyzed the variability of explosive cyclones affecting Europe at different timescales. Cyclones have been identified and tracked through an automatic algorithm that has been applied to the MSLP NCEP reanalysis data. Subsequently, explosive cyclones affecting Europe have been selected from the whole climatology of extratropical North Atlantic cyclones (406 total cases from Oct-Mar 1950-2010). In the first part of the work, the general circulation conditions that appear to be beneficial for the development of explosive cyclones affecting Europe have been assessed through the North Atlantic Oscillation (NAO) characteristics. By using a Daily NAO Index (DNI), results have shown that a positive NAO phase seems to foster such events over Europe. Under this phase, events become more frequent and more intense. This fact can be partially explained by a more intense, northeastwardly displaced and zonally elongated (compared to climatology) Jetstream, which is characteristic of a NAO positive phase. In the second part of the work, multidecadal variability of explosive cyclones has been studied in January through their basic characteristics (average latitude, frequency and intensity). Preliminary results suggest that the Pacific Decadal Oscillation (PDO) might be modulating the average latitude of explosive cyclones affecting Europe. Additionally, a significant correlation was also found at multidecadal scales between the cyclone count and the Atlantic Multidecadal Oscillation (AMO).