Geomagnetic control of the spectrum of traveling ionospheric disturbances based on data from a global GPS network

In this paper an attempt is made to verify the hypothesis of the role of ge omagnetic disturbances as a factor in determining the intensity of travelin g ionospheric disturbances (TIDs). To improve the statistical validity of t he data, we have used the method involving a global spatial averaging of di sturbance spectra of the total electron content (TEC). To characterize the TID intensity quantitatively, we suggest that a new global index of the deg ree of disturbance should be used, which is equal to the mean value of the rms variations in TEC within the selected range of spectral periods (of 20- 60 min, in the present case). The analysis has been made for a set of 100 t o 300 GPS stations for 10 days with a different level of geomagnetic activi ty (Dst from 0 to -350 nT; the Kp index from 3 to 9). It was found that power spectra of daytime TEC variations in the range of 2 0-60 min periods under quiet conditions have a power-law form with the slop e index k = -2.5. With an increase in the level of magnetic disturbance, th ere is an increase in the total intensity of TIDs, with a concurrent kink o f the spectrum caused by an increase in oscillation intensity in the range of 20-60 min. The TEC variation amplitude is found to be smaller at night t han during the daytime, and the spectrum decreases in slope, which is indic ative of a disproportionate increase in the amplitude of the small-scale pa rt of the spectrum. It was found that an increase in the level of geomagnetic activity is accom panied by an increase in the total intensity of TEC; however, it does not c orrelate with the absolute level of Dst, but rather with the value of time derivative of Dst (a maximum correlation coefficient reaches -0.94). The de lay of the TID response of the order of 2 hours is consistent with the view that TIDs are generated in auroral regions, and propagate equatorward with the velocity of about 300-400 m/s.