Abstract
Abstract. A new ionospheric sounding station using a Canadian Advanced Digital Ionosonde (CADI) was established for routine measurements by the "Universidade do Vale do Paraiba (UNIVAP)" at São José dos Campos (23.2° S, 45.9° W), Brazil, in August 2000. A major geomagnetic storm with gradual commencement at about 01:00 UT was observed on 31 March 2001. In this paper, we present and discuss salient features from the ionospheric sounding measurements carried out at S. J. Campos on the three consecutive UT days 30 March (quiet), 31 March (disturbed) and 1 April (recovery) 2001. During most of the storm period, the foF2 values showed negative phase, whereas during the two storm-time peaks, large F-region height variations were observed. In order to study the longitudinal differences observed in the F-region during the storm, the simultaneous ionospheric sounding measurements carried out at S. J. Campos, El Arenosillo (37.1° N, 6.7° W), Spain, Okinawa (26.3° N, 127.8° E), Japan and Wakkanai (45.5° N, 141.7° E), Japan, during the period 30 March-1 April 2001, have been analyzed. A comparison of the observed ionospheric parameters (h'F and foF2) in the two longitudinal zones (1. Japanese and 2. Brazilian-Spanish) shows both similarities and differences associated with the geomagnetic disturbances. Some latitudinal differences are also observed in the two longitudinal zones. In addition, global ionospheric TEC maps from the worldwide network of GPS receivers are presented, showing widespread TEC changes during both the main and recovery phases of the storm. The ionospheric sounding measurements are compared with the ASPEN-TIMEGCM model runs appropriate for the storm conditions. The model results produce better agreement during the quiet period. During the disturbed period, some of the observed F-region height variations are well reproduced by the model results. The model foF2 and TEC results differ considerably during the recovery period and indicate much stronger negative phase at all the stations, particularly at the low-latitude ones.
Highlights
The response of the coupled magnetosphere-ionospherethermosphere system during major geomagnetic storms is one of the key issues related to space weather studies
A major geomagnetic storm with gradual commencement at about 01:00 UT was observed on 31 March 2001
As remarked by Kelley et al (2000) many more people live in these latitude belts than at high latitudes and these investigations assume great importance because ionospheric disturbances or storms may cause operational problems in space communication and navigation systems affecting everyday human activity
Summary
The response of the coupled magnetosphere-ionospherethermosphere system during major geomagnetic storms is one of the key issues related to space weather studies. Solar wind-magnetosphere interactions could affect the midand low-latitude F-region due to intense transient magnetospheric (prompt or direct penetration) convective electric fields (Sastri et al, 1992; Foster and Rich, 1998) and neutral wind (ionospheric disturbance dynamo). In order to study the longitudinal differences during the intense space weather event on 31 March for both mid and low latitudes, the ionospheric measurements obtained on the foF2 (MHz) - model foF2 (MHz). F-region critical frequency (foF2) variations (black) observed at low-latitude stations Sao Josedos Campos and Okinawa during the period 30 March–1 April 2001. The ionospheric sounding measurements obtained at all of the four stations during the period studied are compared with the ASPEN-TIMEGCM model results (Roble and Ridley, 1994) appropriate for the storm conditions
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