Structure of charged particle precipitation in the polar cusp is studied in comparison with the simultaneoulsy observed electric field. The polar cusp is characterized by precipitation of intense low-energy (~100 eV) electrons and energetic (0.1~a few keV/e) ions which often show an energy dispersion. The precipitation region is sometimes divided into two discrete zones which have different disperison characteristics, one showing an ion energy dispersion in which the characteristic ion energy falls with increasing latitude, and the other showing either clear dispersion of different form or non-dispersion. On the other hand, the electric field in the cusp reveals non-uniform and duskward on dawnward convective flows with velocity shears and intense fluctuations. It is remarkable that, nevertheless, ion precipitation shows a clear energy dispersion. We discuss how various types of energy dispersion can be interpreted in terms of the modified velocity filter effect in spite of complexities in the electric field.
Geophysical Research Letters
- Pub Date:
- February 1991
- Magnetospheric Physics: Energetic particles;
- Magnetospheric Physics: Magnetopause;
- and boundary layers;
- Magnetospheric Physics: Electric fields