A new paper in press at Elsevier finds air pressure changes linked to Forbush Decreases in the extra-tropics. These can affect the regime of blocking highs and the landfall of cyclonic weather systems. The paper marks a further step forward in understanding solar-terrestrial relations.
Atmospheric pressure variations at extratropical latitudes associated with Forbush decreases of galactic cosmic rays
I. Artamonovaa,a S. Veretenenkoa,b
a St. Petersburg State University, St. Petersburg 198504, Russia
b Ioffe Physical-Technical Institute, St. Petersburg 194021, Russia
Changes of troposphere pressure associated with short-time variations of galactic cosmic rays (GCRs) taking place in the Northern hemisphere’s cold months (October–March) were analyzed for the period 1980–2006, NCEP/NCAR reanalysis data being used. Notice- able pressure variations during Forbush decreases of GCRs were revealed at extratropical latitudes of both hemispheres. The maxima of pressure increase were observed on the 3rd–4th days after the event onsets over Northern Europe and the European part of Russia in the Northern hemisphere, as well as on the 4th–5th days over the eastern part of the South Atlantic opposite Queen Maud Land and over the d’Urville Sea in the Southern Ocean. According to the weather chart analysis, the observed pressure growth, as a rule, results from the weakening of cyclones and intensification of anticyclone development in these areas. The presented results suggest that cosmic ray vari- ations may influence the evolution of extratropical baric systems and play an important role in solar-terrestrial relationships.
The study of block- ing event formation for undisturbed periods, i.e., the ran- dom (Monte Carlo simulated) 10 day periods with no Forbush decrease effects, showed that the frequency of these events amount to about 43%. Thus, Forbush decreases of GCRs seem to contribute to the intensification of blocking events at middle latitudes. In turn, the forma- tion of blocking anticyclones over the eastern part of the North Atlantic creates an obstacle for the movement of cyclones from the ocean to the continent. This results in the shift of cyclone tracks to the north, as they are forced to bend around the high pressure area, and we can see a statistically significant decrease of pressure at polar lati- tudes of the Northern hemisphere. Thus, the results of the synoptic analysis for the North- ern hemisphere showed that the pressure growth observed in the North Atlantic region in association with Forbush decreases is caused by more intensive formation of block- ing anticyclones. Indeed, blocking anticyclones are high and warm anticyclones which form from cold mobile anti- cyclones over the surface which is relatively warm for the season under study. For this reason they form most fre- quently over the eastern parts of the North Atlantic and Pacific, to the east of warm ocean currents (e.g., Matveev, 1991).
Thus, the presented results suggest the weakening of cyclones and intensification of anticyclone development at middle latitudes of both hemispheres associated with short-time decreases in the intensity of galactic cosmic rays. It is known that the formation and development of extra- tropical baric systems (cyclones and anticyclones) are determined by specific features of the thermo-baric field structure and temperature contrasts in the troposphere (e.g., Vorobjev, 1991). The detected effects allow us to sup- pose that Forbush decreases contribute to the changes in the structure of the thermo-baric field which provides more favorable conditions for anticyclone development. The obtained results suggest an important part of ionization changes for solar activity influence on the lower atmo- sphere dynamics. A possible mechanism of the effects observed in baric system evolution in the course of For- bush decreases may involve cloudiness/aerosol changes associated with variations of ionization and electric current density (Tinsley, 2008). These changes may result in latent heat release and changes in radiative forcing which, in turn, may influence the thermo-baric field of the troposphere.
In this work we carried out the investigation of the response of atmospheric pressure at the level 1000 hPa to Forbush decreases of galactic cosmic rays in both hemi- spheres for the events taking place in the Northern hemi- sphere’s cold period. A significant pressure growth with the maximum on the 3rd–4th days was revealed over Northern Europe and the European part of Russia in the Northern hemisphere. In the Southern hemisphere two regions of a pronounced pressure growth with the maxi- mum on the 4th–5th days were found, the first region is located over the eastern part of the South Atlantic and the second one is over the d’Urville Sea in the Southern Ocean. In both hemispheres the pressure growth was observed at middle latitudes, ?40–70?N and ?40–70?S, correspondingly. Most pronounced pressure deviations are associated with climatic Arctic/Antarctic and Polar fronts, which are the regions of intensive cyclonic activity. According to the weather chart analysis, the detected pres- sure increases are due to the weakening of cyclones and intensification of anticyclones at extratropical latitudes in both hemispheres associated with Forbush decreases under study. The obtained results suggest that variations of galac- tic cosmic rays may influence dynamic processes at middle latitudes, so they may be considered as an important link between solar activity and the lower atmosphere (more…)