DENSITY PROFILE MODIFICATIONS BY ELECTROMAGNETIC ION-CYCLOTRON WAVE PRESSURES NEAR THE DAYSIDE MAGNETOSPHERIC BOUNDARY

It is shown that the existence of the so-called ''magnetic holes'' (ma gnetic field minima) along the field lines play a significant role in the plasma pressure balance in the Earth's magnetosphere. Ponderomotiv e forces induced by the Pc 1 geomagnetic pulsations propagating throug h these regions can lead to a significant plasma accumulation there. A numerical analysis of this effect based on an analytical model for th e geomagnetic field is carried out. The variation of the redistributed plasma density versus radial distance, amplitude, and ratio of wave t o ion cyclotron frequencies is presented. It turns out that density en hancements occur off the equator at high latitudes and that they incre ase when the McIlwain parameter L increases. The specific features of the Pc 1 propagation along the lines of forces in the presence of ''ma gnetic holes'' are discussed. It is suggested that the existence of re gions with decreasing magnetic fields at high-altitude field lines can lead to resonance absorption of ion cyclotron waves (the ''magnetic b each'' effect).