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

摘要

The changes in critical frequency of the F_2 layer (f_oF_2) and f_oF_2 deviation (Δf_oF_2) 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 f_oF_2 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 f_oF_2, but all stations showed a long-duration decrease in f_oF_2 during the recovery phases with Δf_oF_2% 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 f_oF_2 seems to be associated with the prompt penetrating electric fields. Long-duration (>6 hr) decrease in f_oF_2 is mainly accounted to the decrease in thermospheric O/N_2 density ratio because of storm-induced high-latitude circulation of gas with depleted O/N_2 density ratio to lower latitudes and partly due to disturbance dynamo electric fields. A comparison of ionosonde given f_oF_2 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 f_oF_2 for Darwin, Brisbane, and Canberra stations.