The inter-hemispheric asymmetry during June-December storms and the anomalous peak formation: Role of possible anti-seasonal winds

Abstract

The inter-hemispheric difference in the impact of the geomagnetic storms of June 2015 and December 2015 is investigated with respect to quiet time seasonal asymmetry. A meridional chain of ground observatories along 95°E (GNSS receiver/Ionosonde), satellite in-situ measurements (SWARM/COSMIC/C-NOFS), Total Electron Content map and SAMI2/CTIPe model simulations are utilized. Symmetric negative (positive) effects prevailed during the main phase of June (December) storm but hemispheric asymmetry was manifested during the recovery phase. Differential VTEC and NmF2 response in addition to perturbations in VTEC by more than 30 TECU (~90-100%) were recorded. The SWARM observations confirmed that the topside density/TEC enhancement in the southern low latitude was much higher than 300%. The SWARM A/B pass of 23 June and ground TEC map showed a third latitudinal maxima around -45° dip angle in southern hemisphere low latitude in addition to the conventional EIA crests. Similarly an additional peak appeared at +45° dip in northern hemisphere in the SWARM A pass in the sunrise period of 21 December. The higher winter-side hmF2 and northward C/NOFS meridional flow velocity suggest that storm time Joule heating resulted in anomalous equator-ward winds surge in the winter hemispheres of 95°E which led to the formation of the additional storm time maxima at the pole-ward edge of the EIA region. Further modeling efforts are needed to capture this counter-intuitive feature for a better forecasting of the impact of space weather events over low latitude ionosphere.