Isolated ionospheric disturbances as deduced from global GPS network

We investigate an unusual class of medium-scale traveling ionospheric disturbances of the nonwave type, isolated ionospheric disturbances (IIDs) that manifest themselves in total electron content (TEC) variations in the form of single aperiodic negative TEC disturbances of a duration of about 10 min (the total electron content spikes, TECS). The data were obtained using the technology of global detection of ionospheric disturbances using measurements of TEC variations from a global network of receivers of the GPS. For the first time, we present the TECS morphology for 170 days in 1998-2001. The total number of TEC series, with a duration of each series of about 2.3 h (2h 18m), exceeded 850 000. It was found that TECS are observed in no more than 1-2% of the total number of TEC series mainly in the nighttime in the spring and autumn periods. The TECS amplitude exceeds the mean value of the "background" TEC variation amplitude by a factor of 5-10 as a minimum. TECS represent a local phenomenon with a typical radius of spatial correlation not larger than 500 km. The IID-induced TEC variations are similar in their amplitude, form and duration to the TEC response to shock-acoustic waves (SAW) generated during rocket launchings and earthquakes. However, the IID propagation velocity is less than the SAW velocity (8001000 m/s) and are most likely to correspond to the velocity of background medium-scale acoustic-gravity waves, on the order of 100-200 m/s.