We investigate an unusual class of medium-scale traveling ionospheric disturbances (MS TIDs) 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). It was found that TECS are observed in no more than 1-2 % of the total number of radio paths. We present the results derived from analyzing the dependence of TECS parameters on local time, and on the level of geomagnetic activity. The TECS amplitude exceeds at least one order of magnitude the TEC fluctuation intensity under background conditions. To analyze TECS dynamic characteristics the event of 5 October, 2001 was used.
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