Space weather impact on the equatorial and low latitude F-region ionosphere over India

Abstract

Abstract. For a detailed study of the space weather impact on the equatorial and low latitude F-region, the ionospheric response features are analysed during the periods of three recent and most severe magnetic storm events of the present solar cycle which occurred in October and November 2003, and November 2004. The F-layer base height (h'F), peak height (hmF2) and critical frequency (foF2) data, from Trivandrum, an equatorial station and Delhi, a low latitude location, are examined during the three magnetic storm periods. The results of the analysis clearly shows that the height of the F-region (both h'F and hmF2), at the equator and low latitude, simultaneously increases by 200 to 300 km, in association with maximum negative excursion of Dst values around the midnight hours with a large depletion of ionization over the equator, which is followed by an ionization enhancement at low latitude during the recovery phase of the storm. At Delhi, fast variations up to 200 m/s are also observed in the F-layer vertical upward/downward velocity, calculated using Doppler shifts, associated with the maximum negative excursion of Dst. This shows that during magnetic disturbances, the equatorial ionization anomaly (EIA) expands to a much wider latitude than the normal fountain driven by the E/F-layer dynamo electric fields. It is also observed that during the main phase of the storm, at low latitude there is generally an enhancement of F-region ionization with an increase in h'F/hmF2 but in the equatorial region, the ionization collapses with a decrease in h'F/hmF2, especially after sunset hours. In addition, at the equator the normal pre-sunset hours' enhancement in h'F is considerably suppressed during storm periods. This might be due to changes in magnitude and direction of the zonal electric field affecting the upward E×B drift and hence the plasma distribution in the form of a decrease in electron density in the equatorial region and an increase in the low latitude region. In association with disturbance electric fields, the enhanced storm-induced equatorward meridional winds in the thermosphere can also further amplify the F-layer height rise at low latitudes during the post-midnight hours, as observed in two of the storm periods.

Comparison of maximum usable frequency (MUF) variability over Peninsular Malaysia with IRI model during the rise of solar cycle 24

“…Equatorial ionosphere has several characteristic features like the Equatorial Electrojet, Equatorial Sporadic-E, Equatorial Anomaly and Equatorial Spread-F. Therefore, there is a need to study HF frequencies in the equatorial region (Dabas et al 2006;Wichaipanich and Supnithi, 2009;Liu et al 2012) where the diurnal and monthly variations may perform differently in the mid-latitude region. As the equatorial ionosphere has special features, it may consequently pose serious threats to communications and navigation systems compared to the ionosphere over the temperate region Chao et al 2011).…”

On the response of the equatorial and low latitude ionospheric regions in the Indian sector to the large magnetic disturbance of 29 October 2003

“…Significant changes in TEC have also been observed following interplanetary events that are generally attributed to intense disturbance-related electric fields resulting from the magnetosphere-ionosphere interaction processes. The electric fields during geomagnetic disturbances at low latitudes have been attributed to prompt penetration zonal electric fields (Abdu et al, 1995;Sastri et al, 2002;Dabas et al, 2006) and/or delayed disturbance dynamo electric fields (Blanc and Richmond, 1980;Fejer and Scherliess, 1997;Richmond and Lu, 2000;Sobral et al, 2001). It has been shown that these electric fields, depending on their polarity and duration, could produce very significant enhancements or decreases of the vertical TEC.…”

Storm-time ionization enhancements at the topside low-latitude ionosphere

“…Dmitriev (dalex@jupiter.ss.ncu.edu.tw) enhancements of ion and electron density (storm-enhanced density or SED) and temperature at the low-and mid-latitude topside ionosphere are detected by means of in-situ space experiments (e.g. Mannucci et al, 2005;Oyama et al, 2005;Yizengaw et al, 2005) and of remote techniques, such as ionosonde, radar and total electron content (TEC) obtained from GPS signal processing (Tsurutani et al, 2004;Yizengaw et al, 2005;Zhao, et al, 2005;Dabas et al, 2006;Becker-Guedes et al, 2007;Huang et al, 2007).…”