EQUATORIAL PENETRATION OF MAGNETIC DISTURBANCE EFFECTS IN THE THERMOSPHERE AND IONOSPHERE

The neutral dynamic and electrodynamic coupling between high and low l atitudes, and the mutual interactions between these two processes, are investigated. For 22 March 1979, when a sudden increase in magnetic a ctivity occurred, we have analyzed the following experimental data: (a ) neutral densities and cross-track neutral winds as a function of lat itude (0 degrees-80 degrees) near 200 km from a satellite-borne accele rometer; (b) hourly mean K-component magnetic data from the Huancayo O bservatory (0.72 degrees S, 4.78 degrees E; dipole geomagnetic coordin ates) magnetometer; and (c) hourly mean foF2 measurements from the ion osonde at Huancayo. Comparisons are also made with a self-consistent t hermosphere-ionosphere general circulation model and with observationa lly-based empirical models of winds and density. In concert with the i ncrease in magnetic activity to K-p levels of 5-7, a nighttime (2230 L T) westward intensification of the neutral wind approaching 400 +/- 10 0 ms(-1) occurred near the magnetic equator on 22 March 1979, accompan ied by a 35% increase in neutral mass density. About 2 h after each of two substorm commencements associated with periods of southward IMF, similar to 100 gamma and similar to 200 gamma reductions in the daytim e Huancayo H-component (corrected for ring current effects) are interp reted in terms of similar to 0.5 and similar to 1.0 mVm(-1) westward p erturbation electric fields, respectively. An intervening 2-hour perio d of northward IMF preceded a positive equatorial magnetic perturbatio n of about 200 gamma. Time scales for field variations are a few hours , suggesting that processes other than Alfven shielding are involved. Variations in f(o)F2 (similar to +/- 1.0 MHz) over Huancayo are consis tent with the inferred electric fields and magnetic variations. Simila r equatorial perturbations are found through examination of other magn etic disturbances during 1979.