High and mid latitude and near subsolar point ionospheric and thermospheric responses to the solar flares and geomagnetic storms during low solar activity periods of 2017 and 2020

The paper observes the super-imposed effects of intense and moderate solar flares and Coronal Mass Ejection (CME) and High Speed Solar Wind (HSSW) driven geomagnetic storm events on the ionosphere and thermosphere at mid and high latitudes during low solar activity periods. The observations are conducted over a fixed longitude (∼117°W geographic) during May 27–31, 2017 (duration with intense geomagnetic storm without any significant solar flare event), September 3–6, 2017 (duration with solar flare events), September 7–16, 2017 (duration with intense to moderate solar flares as well as geomagnetic storms) and November 28–30, 2020 (duration with a moderate solar flare event with no geomagnetic storm in association). It is found that the effects were the highest during May 27–31, 2017 among all of these events. From the observations of super-imposed effects of the geophysical events, it was found that the effects of an X-class solar flare on September 10–12, 2017 on mid-latitude ionization were suppressed by the Disturbed Dynamo Electric Field (DDEF) from high latitudes during the recovery phase of an intense CME driven geomagnetic storm. The weak effects were also explained by the position of origination of the flare at the Sun. Correlations were observed between the variations in O/N2, neutral wind velocities and the mid and high latitude Total Electron Content (TEC) during these periods. Possible explanation is given for those few cases (for example, September 14, 2017) when the variations in O/N2 mismatched with the local TEC especially in the mid-latitudes. The effects of the solar flare event on November 28–30, 2020 which were short-lived have also been also observed at locations near the subsolar point from low latitudes in the southern hemisphere.