Variation of Vertical Total Electron Content (TEC) Over West Africa during Geomagnetic Storms

Abstract

Changes in vertical total electron content (VTEC) over West Africa which were associated with four geomagnetic storms in 2015 have been studied. The spatial evolution of the quiet time TEC over West Africa for four months (vis; March, June, October and December) which may give rise to unique features of the storm TEC were also evaluated. Quiet-time VTEC (i.e Sq VTEC) was obtained using the hourly means of the international quietest days for each month when a storm of interest occurred. The change in TEC ( ) was obtained after removing the quiet time VTEC from the storm day VTEC. A significant latitudinal variation in VTEC was observed at 22:00LT over West Africa and this was accompanied by the usual broad peak at about 14-17UT. The latitudinal disparity observed in the Sq at 22.00LT was likely driven by the intesification of the fountain effect. The maximum observed during the storms in 2015 were of the other of 16 TECU. These results have important implications for our present understanding of TEC evolution during a geomagnetic and its direct effect on the technologies that depend on it.

Storm‐Time Observations of Traveling Ionospheric Disturbances and Ionospheric Irregularities in East Africa

“…The quiet time data sets (reference ionosphere) were obtained in a procedure suggested by Okpala et al. (2020) based on their Dst values. TEC measurements for GPS arrays considered on March 9, 10, 11, 15 and 16 with their Dst index −1 nT, 6 nT, 4 nT, 6 and 21 nT, respectively, were used to calculate the ratio and percentage of TEC fluctuation.…”

“…During the time when LSTIDs occured, unusual TEC enhancements, that can be considered as positive ionospheric storms, were observed in TEC with ∼20%-105% deviation from the quiet-time TEC although this enhancement were not reflected by ROTI increase, during 17 March 2015. The quiet time data sets were obtained in a procedure suggested by Okpala et al (2020) based on their daily minimum Dst values. The positive ionospheric storm could be generated by thermospheric circulation during geomagnetic storm.…”

“…The quiet time data sets were obtained in a procedure suggested by Okpala et al. (2020) based on their daily minimum Dst values. The positive ionospheric storm could be generated by thermospheric circulation during geomagnetic storm.…”

“…Both ratio and the relative percentage of TEC enhancement were derived by comparing the TEC observation with the average of the quietest 5 days (served as background reference ionosphere) in the same month. The quiet time data sets (reference ionosphere) were obtained in a procedure suggested by Okpala et al (2020) based on their Dst values. TEC measurements for GPS arrays considered on March 9, 10, 11, 15 and 16 with their Dst index −1 nT, 6 nT, 4 nT, 6 and 21 nT, respectively, were used to calculate the ratio and percentage of TEC fluctuation.…”

Comparative Study of the Influence of Full and Partial Halo Geomagnetic Storms on High Latitude Ionosphere

“…They are obtained from WDC, Kyoto, Japan. The quiet (reference ionosphere) was obtained by averaging the first five international quietest days of each month of interest [28]. The months used in this study are June and December, 2015 and January, 2016.…”