Influence of Energetic Solar Proton Events on the Extratropical Cyclone Development in the North Atlantic

The influence of energetic solar proton events, for particle energy above 90 MeV, on the cyclone development at middle and sub-polar latitudes in the North Atlantic was studied, using NCEP/NCAR reanalysis data and weather charts. It was found that the events under study cause an intensification of regeneration (re-deepening) of well-developed cold cyclones near the south-eastern coast of Greenland which is manifested in a significant lowering of pressure levels accompanied by an increase of cyclonic vorticity in the troposphere in this region on the days following the event onsets. A study of the thermo-baric field of the lower troposphere and advective temperature changes associated with SPEs showed that the detected cyclone deepening is due to the increase of cold advection in the cyclone rear when they approach the region of the Arctic front by the Greenland coast. The results suggest a noticeable influence of cosmic particles having sufficient energies to penetrate the stratosphere. An important part in SPE effects seems to be played by the Arctic front which is a region of high temperature contrasts. A physical mechanism of the detected effects may involve changes in the thermo-baric field structure of the lower atmosphere (in particular, an increase of temperature gradients in the frontal zone) creating more favourable conditions for cold advection and in this way contributing to more intensive cyclone deepening. The thermo-baric field changes may be due to radiative forcing and/or latent heat release related to the cloudiness variations.