Comparative analysis of disturbances in the midlatitude ionospheric F 2 layer during strong and extreme magnetic storms in March 2001 according to the data from magnetically conjugate ground ionospheric stations

Abstract

Ionospheric disturbances at heights of the F2 layer maximum during the strong magnetic storm (the minimum value of the Dst index was −149 nT) and the magnetic superstorm (the minimum value of the Dst index was −387 nT) have been compared based on the data from two pairs of magnetically conjugate midlatitude ground stations for ionospheric vertical sounding. The storms began on March 19, 2001, and March 31, 2001, respectively. It has been obtained that almost only negative ionospheric disturbances were observed in the Northern and Southern hemispheres in both cases. The maximum effect in changes in the layer critical frequency (foF2) in both hemispheres has a time delay relative to the moment of the maximum disturbance in the Dst index on the order of 3–4 h for the strong storm and about 1 h for the superstorm. The disturbed variations in the foF2 critical frequency in different hemispheres correlate well with each other in the plane of one magnetic meridian, but the correlation substantially weakens at different magnetic longitudes. An assumption is made that the revealed features of the behavior of the disturbed midlatitude ionospheric F2 layer are caused by the complex character of the thermospheric response to the energy release in the auroral zone during the considered magnetic storms.