GPS observations of post-storm TEC enhancements at low latitudes
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2006
Received: 16 February 2006
Accepted: 3 July 2006
Published: 25 December 2006
In a previous work (J. Geophys. Res., 110(A01308), 1–11, 2005), the authors developed an original approach to the processing of total electron content (TEC) data obtained by GPS signals from the Japan receiver network. This approach includes removing the diurnal and seasonal variation carried by 27-day medians and the solar rotation periodicity. The relative deviations of TEC from the median—from all measured locations at a given hour—were then approximated by a regression line along the main prolongation of the Japan islands, between latitudes 24° and 45°N. The two variables of the regression line, the average value at the center and the slope were obtained as a time series, and their behavior during geomagnetic storms in the period 2000–2002 were analyzed. One interesting result was the observed enhancement of TEC at the end of the recovery phase of the storms. The slope variations clearly showed that this enhancement started from the south and was interpreted as a poleward expansion of equatorial crest. In the present paper we further analyze this post-storm phenomenon, adding foF2 data from Japanese Kokubunji and Okinawa ionosondes. We also show the latitude extension of the poleward expansion by using lat/UT contour plots. The results confirm that most of the post-storm TEC enhancements are part of the equatorial crest region which extends poleward during nighttime. In some cases, the enhanced TEC structures develop by separating from the crest region. Daytime TEC enhancements were also observed. Their structures are not confined to the equatorial crests region, but occupy the whole latitude range considered in this study. TEC post-storm enhancements were generally found to be in agreement with foF2 variations.