Ionospheric Disturbances during the Period 30 April to 5 May 1976.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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Ionospheric behavior during solar disturbances and some theories of ionospheric storm mechanisms are reviewed. Variations in ionospheric parameters, fmin and foF2, from median values for May 1976 are analyzed using data from 72 ionospheric stations around the globe. Geomagnetic, auroral, interplanetary, and solar data are included in this analysis. The major solar flare on 30 April 1976 was followed by a typical enhancement of ionospheric D-region absorption in the sunlit hemisphere, but no appreciable change in foF2. An ionospheric substorm occurred over Europe following the 1200 UT 2 May 1976 geomagnetic substorm. The geomagnetic SSC at 1830 UT on 2 May 1976 was followed six hours later by a sharp ring current increase, a large geomagnetic substorm, and a sudden F-region disturbance on the dayside hemisphere. Peaks in foF2 appeared on the three storm days, 3-5 May 1976, over Japan at about 1-2 hours following local sunrise. Travelling ionospheric disturbances TIDs propagated toward the equator with apparent horizontal velocities ranging from 718 to 368 msec, and periods averaging 2.5 hours. The sources of these TIDs probably lay in the northern-hemisphere auroral zone. Finally, the F-region variations are discussed in terms of theories of ionospheric storm mechanisms, including ExB drifts, thermospheric winds, and composition changes. Geomagnetic substorm time electric fields are suggested as a plausible source of ionospheric disturbances in middle and low latitudes.
- Atmospheric Physics