IONOSPHERIC CHANGES IN RESPONSE TO IMF VARIATIONS

This paper attempts to summarize the results of investigations of IMF effects on the ionosphere. published mostly in Russian, and to place t hem in context in up-to-date knowledge of IMF/magnetosphere/ionosphere relationships. Effects of the IMF sector structure and of the IMF B-z component turnings on the ionospheric F-layer are considered, includi ng variations of position of the main ionospheric trough (MIT). The pa per includes results of both theoretical calculations and observationa l data obtained mostly by the Cosmos-900, Intercosmos-19 and Cosmos-18 09 satellites at subauroral, middle and low latitudes. The MIT positio n dependence on longitude has been derived as a background for Further study. It has been shown that the nightside winter trough position at the storm growth phase correlates best with K-p index taken with a ti me delay tau, which is proportional to a disturbance growth rate Delta K-p/Delta t. The MIT position dependence on D-st, B-z and B-y is also shown. Two troughs have been found to be formed usually in the storm recovery phase at postmidnight hours: these are the MIT (main ionosphe ric trough) and RIT (ring ionospheric trough) associated with the DR-c urrent. In general the MIT position's response to B-z southward turnin gs corresponds well to changes of the auroral diffuse precipitation eq uatorial edge. For B-z southward turnings the height of the equatorial night-lime F-layer lowers, and at equatorial latitudes f(o)F2 decreas es sharply, the latter effect being most pronounced at 03 LT. Large-sc ale internal gravity waves arriving at equatorial latitudes from the a uroral oval cause intensification of the equatorial anomaly, both in d aytime and night-time. A schematic pattern of a global ionospheric res ponse to a magnetic disturbance is constructed using as an example the strong storm on 3-4 April 1979.