Geomagnetic forcing of changes in climate and in the atmospheric circulation

Common features in records of solar and geomagnetic activity as well as of climatic parameters can be observed. High correlation coefficients were Found between geomagnetic activity, the sea level atmospheric pressure and the surface air temperature, occurring with a positive sign in the middle and southern Europe, in the south-eastern part of North America and in the western Atlantic but with a negative sign in the northern Atlantic and Canada. In the hypothesis proposed here for explaining Sun-weather relations, downward winds following the geomagnetic storm onset are generated in the polar cap of the thermosphere and penetrate to the stratosphere and troposphere, where the atmospheric response can be observed as a sudden increase of pressure and temperature. The subsidence effects along the northern margin of the subpolar high pressure areas (mainly the Siberian high) are accelerated and strong eastward winds participate in the intensification of the northern jet stream and in the successive zonalization of how in mid-latitudes. It is shown that at a time of low geomagnetic activity planetary waves with large amplitudes prevail in the northern hemisphere due to the orographic effect of the Rocky Mountains and Greenland. On the other hand, at a lime of high geomagnetic activity, an intensification of the winds can be observed not only in the thermosphere but also in the troposphere. A strong northern jet stream participates in the intensification of the westerly zonal flow and in the increase of temperature successively in the eastern part of North America, in Europe and northern Asia. These relations are clearly detectable not only in monthly averages of the pressure and temperature distribution but also in the daily variations of atmospheric circulation. The results enable us to test a causal link of the Sun-weather processes, to explain strong interannual climate and weather changes in several key regions of the northern hemisphere, mainly in winter, and to study possible causes of the North Atlantic Oscillation. The results obtained contribute also to the study of the occurrence of long-term cyclic changes which were observed both in solar and geomagnetic activity and temperature T, as well as in the radioactive Delta(14)C, and have a similar trend. A composite curve was suggested by summing up sinusoidal curves with periods 70, 200, 800 and 2400 years roughly representing changes of all three mentioned parameters (aa, T and Delta(14)C) during the past 1600 years and their probable trend for the next 800 years. The results seem to imply that the global warming could be slowed down in next decades, because the natural component influencing the increase of temperature in the 20th century will most probably decrease in the next century due to the weaker external geomagnetic forcing which was suggested to modify natural meteorological processes. (C) 1998 Elsevier Science Ltd. All rights reserved.