CENTRAL PLASMA SHEET ION PROPERTIES AS INFERRED FROM IONOSPHERIC OBSERVATIONS

A method of inferring central plasma sheet (CPS) temperature, density, and pressure from ionospheric observations is developed. The advantag e of this method over in situ measurements is that the CPS can be stud ied in its entirety, rather than only in fragments. As a result, for t he first time, comprehensive two-dimensional equatorial maps of CPS pr essure, density, and temperature within the isotropic plasma sheet are produced. These particle properties are calculated from data taken by the Special Sensor for Precipitating Particles, version 4 (SSJ4) part icle instruments onboard DMSP F8, F9, F10, and F11 satellites during t he entire year of 1992. Ion spectra occurring in conjunction with elec tron acceleration events are specifically excluded. Because of the var iability of magnetotail stretching, the mapping to the plasma sheet is done using a modified Tsyganenko [1989] magnetic field model (T89) ad justed to agree with the actual magnetotail stretch at observation tim e. The latter is inferred with a high degree of accuracy (correlation coefficient similar to 0.9) from the latitude of the DMSP b2i boundary (equivalent to the ion isotropy boundary). The results show that temp erature, pressure, and density all exhibit dawn-dusk asymmetries unres olved with previous measurements. The ion temperature peaks near the m idnight meridian. This peak, which has been associated with bursty bul k flow events, widens in the Y direction with increased activity. The temperature is higher at dusk than at dawn, and this asymmetry increas es with decreasing distance from the Earth. In contrast, the density i s higher at dawn than at dusk, and there appears to be a density enhan cement in the low-latitude boundary layer regions which increases with decreasing magnetic activity. In the near-Earth regions, the pressure is higher at dusk than at dawn, but this asymmetry weakens with incre asing distance from the Earth and may even reverse so that at distance s X < similar to-10 to -12 R-E, depending on magnetic activity, the da wn sector has slightly higher pressure. The temperature and density as ymmetries in the near-Earth region are consistent with the ion westwar d gradient/curvature drift as the ions ExB convect earthward. When the solar wind dynamic pressure increases, CPS density and pressure appea r to increase, but the temperature remains relatively constant. Compar ison with previously published work indicates good agreement between t he inferred pressure, temperature, and density and those obtained from in situ data. This new method should provide a continuous mechanism t o monitor the pressure, temperature, and density in the magnetotail wi th unprecedented comprehensiveness.