Ionospheric Response to the St. Patrick's Day Space Weather Events in March 2012, 2013, and 2015 at Southern Low and Middle Latitudes

Abstract

AbstractThe changes in critical frequency of the F2 layer (foF2) and foF2 deviation (ΔfoF2) have been determined for three geomagnetic storms in March of the years 2012, 2013, and 2015 at low‐latitude stations, Darwin (geomag. lat. 21.96°S) and Townsville (28.95°S), and midlatitude stations, Brisbane (36.73°S), Canberra (45.65°S), and Hobart (54.17°S). The moderate storm during 15–16 March 2012 (Dst = −87 nT) showed a decrease in foF2 at midlatitude and no effect at low‐latitude stations. For the intense storm of 17–18 March 2013 (Dst = −132 nT) and the super storm of 17–18 March 2015 (Dst = −222 nT), some middle‐ to low‐latitude stations showed a short‐duration increase in foF2, but all stations showed a long‐duration decrease in foF2 during the recovery phases with ΔfoF2% varying from 26% (Darwin) to 36.6% at Hobart for the March 2013 storm and above 40% for the March 2015 storm at all of the stations. Short‐duration (~2–4 hr) increase in foF2 seems to be associated with the prompt penetrating electric fields. Long‐duration (>6 hr) decrease in foF2 is mainly accounted to the decrease in thermospheric O/N2 density ratio because of storm‐induced high‐latitude circulation of gas with depleted O/N2 density ratio to lower latitudes and partly due to disturbance dynamo electric fields. A comparison of ionosonde given foF2 for equinoctial storms (March 2013 and 2015) with similar strength Southern Hemisphere winter storms (July 2012 and June 2015) has been made with the IRI‐2016 model foF2 for Darwin, Brisbane, and Canberra stations.