Behavior of Auroral Zone Total Electron Content During Substorms

The auroral zone total electron content TEC as computed from the ATS-3 Faraday-rotation shows systematic changes during magnetic activity. These changes depend upon local time, season, sunspot-cycle and the prehistory of the magnetic activity. During summer and equinox the daytime TEC both shows a positive and negative phase, which probably are related to the prehistory of the magnetic activity. During winter the daytime TEC is dominated by enhancements as responses to the substorms. The magnitude of these enhancements is determined by the activity prior to sunrise. Thus if the activity is low prior to sunrise, the substorms during the subsequent day cause the TEC to blow up. In contrast if the pre-sunrise activity is high the daytime TEC is similar to the quiet time level. In the late afternoon the TEC is depleted at all seasons as a response to the substorms. in the night enhancements are observed due to the precipitation of substorm-injected electrons. These enhancements are very large during winter. During summer other factors cause a depletion of TEC. At sunspot maximum the net result is a depletion and at sunspot minimum an enhancement. (Author)