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High-altitude cusp positions sampled by the Hawkeye satellite

1997; Elsevier BV; Volume: 22; Issue: 7-8 Linguagem: Inglês

10.1016/s0079-1946(97)88121-9

1879-3568

Shing F. Fung, T. E. Eastman, S. A. Boardsen, S.-H. Chen,

Geomagnetism and Paleomagnetism Studies

The Hawkeye satellite, with its almost 90° inclination and 21 RE apogee, provided the most extensive sampling to date of the exterior cusp as well as the high-latitude magnetopause. Using a combination of plasma, magnetic field, and plasma wave observations sampled between 1974 and 1978, we have identified 211 crossings of the exterior cusp, of which 175 have solar wind pressure and 136 have simultaneous IMP-8 interplanetary magnetic field (IMF) data available. This ensemble of cuts through the exterior cusp region was then statistically analyzed to determine possible variations of average cusp position with changes in IMF orientation or solar wind pressure. Our analyses show that the exterior cusp region (> 4 RE) is best ordered in Solar Magnetic (SM) coordinates. It has an average magnetic latitude of about 62° and average invariant latitude near 81°. There is substantial inward and outward radial distance change with changing solar wind pressure. The Hawkeye exterior cusp samples show weak or no dependence on IMF orientation, at least for changes on time scales longer than about one hour. Effects due to shorter time-scale variations, like those most often seen at low-altitudes, would not be apparent in our statistical results. Comparison of the Hawkeye samples of the exterior cusp with low-latitude magnetopause observations suggests that the frontside magnetosphere is asymmetric with more stretching in the polar direction.