FORECASTING IONOSPHERIC STRUCTURE DURING THE GREAT GEOMAGNETIC STORMS

Characteristics of midlatitude ionospheric disturbances during several great geomagnetic storms have been investigated using data from the E uropean geomagnetic observatories and ionospheric stations with the ai m of developing the local forecasting models, as part of the predictio n and retrospective ionospheric modeling over Europe project, Based on the analysis of the geomagnetic storms of February 6, 1986, and March 13, 1989, a detailed picture of the local H component of geomagnetic field and the ionospheric critical frequency f(o)F(2) variations is pr esented, The results show that f(o)F(2) was dramatically changed above or below the monthly median level in a relatively narrow band about 1 5 degrees of latitude and 30 degrees longitude during the different ph ases of the storms, These results support the view that day-to-day F r egion ionospheric variability is essentially altered in great storms, Consequences of those effects for short-term modeling purposes are dis cussed.