Detection of the ionospheric response to solar flares based on the GPS global net of data

A new method for detecting solar flare effects on the ionosphere based on d ata of the international network of two-frequency multichannel receivers of the GPS (GLOBDET) navigation system has been proposed. The developed techn ique substantially improves the sensitivity and space-time resolution of th e observations as compared to known radiophysical methods. The proposed met hod includes the application of consistent filtration and coherent processi ng of the variations in the total electron content (TEC) in the ionosphere. In this case, TEC is simultaneously determined from GPS data for the whole set of GPS satellites visible in the given time interval over the entire G PS global net of stations chosen for an analysis. The number of these satel lites reaches 5-10. It has appeared that the TEC fluctuations obtained afte r eliminating the TEC linear trend with a time window of about 5 min are co herent for all stations and rays of the GPS satellites on the dayside of th e Earth. If the relaxation time of the electron density disturbance in the ionosphere is of the order of 50-100 s, the time profile of TEC responses i s similar to the time dependence of rigid X-ray variations during solar fla res in the energy range of 25-35 keV. On the nightside of the Earth, a simi lar effect has not been observed.