Climatological response of Indian low‐latitude ionosphere to geomagnetic storms

Abstract

A climatological response of low‐latitude ionosphere to geomagnetic storms is presented using long‐term global ionospheric maps data from June 1998 to June 2015 covering two solar cycles 23 and 24. The results are presented for daytime forenoon and afternoon sectors under minor, moderate, and major ionospheric storm categories based on minimum Dst index criterion. For the first time the effectiveness of storms is identified using monthly standard deviation as an indicator of the day to day variability in equatorial and low‐latitude ionosphere. Thus, results on climatology are definitive and form a database that would be comparable to statistical results from any other longitude and time. Seasonal statistics for total storms, effective positive and negative storms, and amplitude of mean seasonal perturbation in total electron content are obtained. Total and effective storms are found to be higher in solar cycle 23 than in 24 and only a couple of effective storms occurred during low solar activity 2007–2009 that too in minor category. Afternoon sector is found to be favorable for occurrence of maximum number of effective positive storms. A latitudinal preference is found for a given storm to be effective in either time sectors. Equinoctial asymmetry in ionospheric response both in terms of occurrence and perturbation amplitude is found. September equinoxes are found to bear maximum total, effective positive and negative storms. Winters are found more prone to negative storms, whereas summers have recorded minimum number of either of storms and minimum perturbation amplitudes.

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

“…Storms from this list along with similar storms from solar cycle 24 have been taken up in the present study. Following the definition of effective ionospheric storms by Suresh and Dashora (2016), storms with minimum Dst between −100 and −200 nT are termed as moderate storms and those with minimum Dst ≤ −200 nT as major storms. Successive storms occurring on consecutive days are analyzed only for the first day (or the MP) and rest of the consecutive stormy events are not analyzed.…”

“…Thus, a total of 31 geomagnetic latitudes are chosen and corresponding set of geographic coordinates were obtained using quasidipole geomagnetic coordinate calculator (Emmert et al, 2010) which are shown in Figure 1. Quiet time monthly mean GIM VTEC and its corresponding standard deviation for each selected coordinate are computed following Suresh and Dashora (2016). GIM data provide global gridded VTEC values with size of 2.5°× 5°in geographic latitude-longitude for given UT (Jee et al, 2010).…”

“…Then the differences of dualfrequency phase and code measurements are formed to get slant TEC observations. Some studies indicate the use of Dst index to be more insightful when deducing effects of storms in low latitudes (Immel & Mannucci, 2013;Suresh & Dashora, 2016) The trained weights are used to transfer the learning for the set of corresponding inputs on a given day using ΔH observations. The leveled slant TEC is then corrected for differential code biases associated with each satellite and individual receiver.…”

“…Finally, time series of VTEC for each ionospheric pierce point for a given satellite pass is obtained by multiplying slant TEC with an elevation dependent mapping function (Ma & Maruyama, 2003). To showcase storm time positive/negative deviations in VTEC for a given latitude (Suresh & Dashora, 2016), diurnal monthly mean VTEC of quiet days corresponding to the month of the storm along with standard deviation of VTEC for the range of latitudes is obtained. Simultaneous rise and fall of VTEC observed from multiple satellites over a single Since the precious and coveted E × B drift observations from Jicamarca radar are not available for all the storms, a neural network-based E × B drift model is specifically developed in the present study using ΔH measurements (Anderson et al, 2002(Anderson et al, , 2004.…”

“…Monthly mean is entrusted to bear the seasonal background of prevailing electric field and neutral meridional winds and if the difference VTEC is larger (smaller) than the standard deviation, it shall exhibit effective positive (negative) ionospheric effect at that time at any latitude (Suresh & Dashora, 2016). Monthly mean is entrusted to bear the seasonal background of prevailing electric field and neutral meridional winds and if the difference VTEC is larger (smaller) than the standard deviation, it shall exhibit effective positive (negative) ionospheric effect at that time at any latitude (Suresh & Dashora, 2016).…”