The Characteristics of Polar CAP Precipitation and Their Dependence on the Interplanetary Magnetic Field and the Solar Wind

Abstract

Work completed on the nature of the precipitation occuring in the polar cap and its relationship to the state of the solar wind and the interplanetary magnetic field is reviewed. This work has shown that there are two states of polar-cap precipitation; an active state occurring when the IMF B/sub z/ component is positive in which polar showers or polar squalls occur over much of the cap and a quiet state occurring when the IMF B/sub z/ is negative in which only the unperturbed polar rain is observed. The two states occur with approximately equal frequency. The characteristics of both the precipitating electrons and ions for the two states and the variation in these characteristics with the orientation of the IMF and the state of the solar-wind plasma are discussed along with the implications of these observations as to the mechanisms leading to these two states.