Eects of geomagnetic activity on the mesospheric electric ®elds*

The results of three series of rocket measurements of mesospheric electric ®elds carried out under di€erent geomagnetic conditions at polar and high middle latitudes are analysed. The measurements show a clear dependence of the vertical electric ®elds on geomagnetic activity at polar and high middle latitudes. The vertical electric ®elds in the lower mesosphere increase with the increase of geomagnetic indexes Kp and P Kp. The simultaneous increase of the vertical electric ®eld strength and ion conductivity was observed in the mesosphere during geomagnetic disturbances. This striking phenomenon was displayed most clearly during the solar proton events of October, 1989 accompanied by very strong geomagnetic storm …Kp ˆ 8‡†. A possible mechanism of generation of the vertical electric ®elds in the mesosphere caused by gravitational sedimentation of charged aerosol particles is discussed. Simultaneous existence in the mesosphere of both the negative and positive multiply charged aerosol particles of di€erent sizes is assumed for explanation of the observed V/m vertical electric ®elds and their behaviour under geomagnetically disturbed conditions.