Consistent features of TEC changes during ionospheric storms

Global position system (GPS) data from the continuously operating reference stations (CORS) network have been used to obtain the ionospheric vertical total electron content (VTEC) values over the continental USA (CONUS), corresponding to a series of 10-day storm periods with good seasonal coverage. The VTEC values have been extracted using the data assimilation algorithm for ionospheric imaging (MAGIC) package, a Kalman filter based code. The storm response of the VTEC was extracted from the data as a ratio to the quiet periods preceding the storms, and sorted as a function of latitude and a storm index defined as the integral, or filtered, a(p) over the previous 33 h. When studying the 10-day periods, consistent features from storm to storm were found, and these features became more apparent when separating the data between the "driven" phase of the storm, when the integral of a(p) is rising, and the "recovery" to the storm, when the integral of a(p) is declining. In this paper the results for three storms are highlighted. The "driven" phase shows, for these storms, a positive phase for the mid latitude region, while the "recovery" shows a negative phase. The existence of the positive phase over CONUS at the beginning of the storm period appears to be related to the timing of the peak of the perturbation; a positive phase will be observed when the peak of the perturbation occurs near midnight UT. (C) 2006 Elsevier Ltd. All rights reserved.