Study of the Thermospheric-Ionospheric Response to Intense Geomagnetic Storms at Middle Latitudes

摘要

The ionospheric response to enhanced geomagnetic activity was studied in terms of two ionospheric parameters, f_oF2 and h'F2, aiming the investigation of the middle latitude positive and negative ionospheric storm effects characteristics. Simultaneous observations from a chain of several middle latitude stations distributed in longitude around the earth during two intense geomagnetic storms (Dst < -100 nT), were analyzed in this work. The correlation results between the f_oF2 and h'F2 disturbances and the Dst geomagnetic index verified that the morphology of middle latitude ionospheric disturbances in response to geomagnetic storms shows a great degree of variability and a strong dependence on local time observation. Negative deviations constitute the typical ionospheric response. In general it is reported that the F2 layer virtual height h'F2, which is observed only during daytime in conjunction with F1 layer presence, shows clear response to magnetic storm activity. On the other hand, positive ionospheric disturbances are accompanied by weak height enhancements. Real observations were also compared to the thermospheric-ionospheric view associated with positive and negative storm effects proposed by Prolss (1993). This test clearly demonstrates that such a model can capture most of the basic aspects of ionospheric storms, taking into consideration that any new burst of activity is associated to a new disturbance zone, resulting to the formation of a large zone of disturbance that covers the post-midnight and the forenoon sector as well. This mechanism may be the cause of long lasting negative storm effects observed as the typical ionospheric response to geomagnetic storm activity.