Response of low-latitude ionospheric total electron content to the geomagnetic storm of 24 August 2005

Abstract

[1] Response of low-latitude ionosphere to the geomagnetic storm of 24 August 2005 has been studied using total electron content (TEC) data obtained from the Global Positioning System (GPS) receivers. These studies were carried out using the receivers that were located (1) near the northern crest (∼15°N mag. Lat.) of the equatorial ionization anomaly around 56°E, 74°E, and 102°E longitude and (2) from the northern crest of the ionization anomaly down to the magnetic equator in the longitude belt 75°E ± 3°E. These studies have been substantiated with the ground-based magnetometer data at Tirunelveli and Alibag, an equatorial and off equatorial station, respectively. The ground-based ionosonde data at New Delhi, a low-latitude station, have also been used to substantiate the TEC observations. The storm day TEC shows two well-defined humps at all stations wherein enhancements of the order of 80%-100% have been observed. While the first of the enhancements has been attributed to the prompt penetration electric field associated with an interplanetary electric field (IEF Ey) of about 35 mV/m, the other one has been attributed to the second episode of the prompt penetration electric field (IEF Ey ∼ 20 mV/m) and abnormal equatorial plasma fountain in late evening hours, respectively. During the unsteady ring current conditions when the IMF Bz was still southward, penetration of a westward electric field has been inferred. Two peaks in foF 2 have been observed whose time of occurrence coincides with those of the humps in the low-latitude TEC. Results from stations having nearly the same magnetic latitude show that the ionospheric response, in terms of GPS TEC, to the prompt penetration electric fields is longitudinally independent. Formation of the first hump in TEC is progressively delayed in time from low to near-equatorial latitudes for stations in different magnetic latitudes along nearly the same longitude. However, its time of appearance at Diego Garcia, a station magnetically conjugate to Udaipur, is the same as that at Udaipur. The results also reveal the poleward expansion of the ionization anomaly due to the storm. Disturbance dynamoelectric fields have been inferred to be responsible for the suppressed plasma fountain, resulting in suppressed TEC values and equatorward contraction of the ionization anomaly on 25 August, compared to a reference quiet day.

Response of low latitude ionosphere to the geomagnetic storm of May 30

“…The average values of ASY-H and AE during this period were close to 120 nT and 1200 nT, respectively. Although ASY-H and AE were high, unlike the earlier works (Fejer et al 2007;Sharma et al 2011b) the magnetometer data in the present case did not reveal any additional fields arising due to the disturbed ring currents implied by high AE and ASY-H indices. The SYM-H attained a maximum of −120 nT around 1100 UT.…”

“…Most of the studies in the region are concerned with the major storms of either May 15, 2005(Dashora et al 2009Bagiya et al 2011;Sharma et al 2011c) or August 24, 2005(Sreeja et al 2009Kumar and Singh 2011b;Sharma et al 2011b). Recently Kumar and Singh (2011a) have reported the TEC variations during the moderate geomagnetic storms that occurred in the low solar activity period 2007-2008.…”

“…Their effect in low latitudes during the daytime could be inferred from the weakened or suppressed equatorial electrojet (e.g., Sharma et al 2011b). In a number of earlier studies (Tsurutani et al 2004;Dashora and Pandey 2007;Sharma et al 2011b), reduction in electron density, or the total electron content has been attributed to the DD fields.…”

“…On the other hand, in a different case study wherein the IMF Bz was steady and southward for a long duration, Fejer et al (2007) have reported multiple penetrations of both the eastward as well as westward electric fields on the dayside of the globe when the ring currents were high and unsteady. Recently, Sharma et al (2011b) have reported the episode of penetration of a westward PP field during the daytime when the ring current activity was high even though the IMF Bz was southward.…”

Interhemispheric Asymmetry in Response of Low‐Latitude Ionosphere to Perturbation Electric Fields in the Main Phase of Geomagnetic Storms

“…The delayed start in rise of TEC can be explained by redistribution of uplifted plasma aided by the slower (morning) production at lower altitudes to maintain the continuity (Dashora et al, 2009;Heelis et al, 2013;Rishbeth et al, 2010). The episodic variations in ASYM-H index during the MP of this storm and its effect on low-latitude magnetometer observations of H component were emphasized by Sharma et al (2011). The hemispherical asymmetry in amplitude of perturbation component of VTEC during PPEF is also evident in both cases.…”