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.