GPS observations of post-storm TEC enhancements at low latitudes

Abstract

In a previous work (J. Geophys. Res., 110(A01308), [1][2][3][4][5][6][7][8][9][10][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.

Ionospheric specification with analytical profilers: Evidences of non-Chapman electron density distribution in the upper ionosphere

“…At the end of the geomagnetic storm, TEC rel becomes positive again, a phenomenon known as a "post-storm enhancement" (PSE). It is similar to the one observed in the Asian sector (Kutiev et al, 2005;2006b) and is explained with the electro-magnetic drift effects of the convection electric field penetrating deep into the low/equatorial latitude ionosphere. Most of the PSE events appear to also depend on local time (late afternoon to early evening hours).…”

“…A post-storm increase in TEC is also known (Kutiev et al, 2006b;Stankov et al, 2010). Considering the above analysis, in such situations apparently the Chapman profiler should be better suited for modelling purposes.…”

“…It should be noted, however, that at all topside TEC values there are profiles with an a-Chapman shape. This is to be expected, since the data was taken at all possible local times and seasons and at different magnetic longitudes and latitudes; it is well known that the storm time behaviour at different times and location can be very different (Ondoh, 1967;Sato, 1968;Warren, 1969;Fuller-Rowell et al, 1994;Kutiev and Muhtarov, 2001), and it should be noted that a TEC value that is considered depleted at certain times and locations might be a normal, quiet time value at others (Kutiev et al, 2005;2006b). The same issues exist with regard to the topside slab thickness (defined as the topside TEC divided by the peak electron density), which are displayed in Fig.…”

Temporal change of EIA asymmetry revealed by a beacon receiver network in Southeast Asia

“…As shown in Fig. 5a, c, the σ and average TEC in the daytime during the disturbed days are large compared to those during the quiet days, and similar behaviors have been described in other reports (Kutiev et al 2006;Lin et al 2007b;Kumar et al 2014). The high σ around the EIA crests during the disturbed days could be caused by the highly variable penetration of the electric field that controls the strength of EIA.…”

Prestorm enhancements in NmF2 and total electron content at low latitudes

“…The observation that the negative phase is observed first at Wakkanai and then propagates to lower latitudes is just what is expected as a consequence of equatorward propagation of neutral composition disturbance from auroral oval [ Prolss , 1995]. The storm‐time behavior at low latitudes in the Japanese sector during this storm has been studied in detail by Kutiev et al [2006].…”