Investigation on mid-latitude stations to storm-time variations of GPS-TEC

The ionospheric response to some selected storm events, occurring at different seasons, was studied using the Global Positioning System (GPS) measurements obtained from the International GNSS Service (IGS) receivers located at four mid-latitude stations comprising the northern and southern hemispheres. The inter-hemispheric comparison of the total electron content (TEC) variation during these solar events reveals clear hemispheric and seasonal asymmetries. Generally, the TEC deviation, relative to the reference quiet time averaged values, reveals strong latitudinal dependence within the mid-latitude region. The trend in the variation of TEC over the two stations in the northern hemisphere is similar, whereas some similarities/differences are generally observed over the two southern stations. We suggested that in evaluating the storm-time TEC variation over the mid-latitude, it is essential to differentiate precisely between the global, regional and local characteristics. Mechanisms considered to be responsible for the ionospheric behaviours during these storm events are also discussed.