Ionospheric incoherent scatter measurements with the MU radar: Observations of F-region electrodynamics.

Abstract

The MU (Middle and Upper atmosphere) radar of Japan is a 46.5-MHz, pulse-modulated, monostatic, Doppler radar with an active phased-array antenna which consists of 475 crossed Yagis. This system has been used primarily, since its initial observations with a partial system in 1983, to observe the coherent backscatter from irregularities in the troposphere, stratosphere, and mesosphere (MST radar). However, this system was also designed to be able to observe the weak incoherent scatter (IS) from the free electrons of the ionosphere. We report here the first observations of ionospheric electrodynamics using the IS capability of the MU radar. We show several examples of measurements made with one-hour time resolution for one or two days duration and then the mean behavior resulting from an average of eight experiments. We compare these results with an empirical model of electric fields derived from measurements from other incoherent scatter radars. We find good agreement between the model and the MU radar measurements for the perpendicularnorth drifts, except for the existence of some fluctuations with an 8-hour period, which we suspect will disappear from the MU mean behavior once more data are available to average. We also find good agreement between the model and measurements for the diurnal component of the perpendicular-east drifts, but the measurements additionally exhibit a semi-diurnal component of strength similar to that of the diurnal component while the model shows only a small semi-diurnal component. We also show several examples of an apparently strong control of the night-time ionospheric drift by the F-region dynamo mechanism, especially on the shorter time scales. Finally, we show one example of a very unusual oscillatory behavior (amplitude varying from 30 to 60m/s, period varying from 4 to 7 hours) in the perpendicular-east velocity, while the other velocity components remained normal, during a continuous day and a half period during the GITCAD campaign of January 28-30, 1987.