Temporal and Spatial Variability of the Mid-latitude Ionosphere and Thermosphere

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The principal results are summarized as follows. (i) Ionospheric/thermospheric seasonal behavior-four years of MU radar data are analyzed to understand the seasonal variations, solar activity dependence, and magnetic activity behavior of the electron and ion density and temperature. Based on these data, the thermospheric temperatures and densities are derived. The temperatures are consistently lower than existing model values by 2-156 K,depending upon solar activity and season. (ii) The seasonal behavior of F-region electron density is investigated in detail. (iii) Seasonal behavior of ion-drift velocities-MU radar observations of electric fields during September 1986 to January 1991 are investigated in the form of time-of-day variations for several different seasonal and solar-activity cases. The maximum daily amplitudes and the time-of-day and solar activity trends at the MU and the Arecibo radar locations have strong resemblances. However the seasonal trends in the MU data, the Arec … More ibo data, and existing radar models disagree strongly. Currently, the thermospheric meridional winds are being investigated from these results. (iv)Mid-latitude ionospheric disturbances-over 500 hours of multiple-beam radar observations are analyzed. During magnetically disturbed times the traveling disturbances are very predominantly equatorward, indicating an auroral wave source, while during quiet times all wave directions are observed, indicating a local, lower-atmosphere source. (v) Ionospheric structure during the low-latitude auroral event of 20-23 October 1989-during the first auroral display over Japan since 1960, extreme spatial and temporal gradients are observed in four oblique beams. This observation calls into doubt the validity of the monostatic, sequential-three-position, vector velocity measurement often made by radars.All of these results are essentially "local" investigations overhead from the MU radar. It strongly hoped that further efforts will be made in the near future to expand these studies to consider "non-local" phenomena related to global forcing mechanisms. Less