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Ann. Geophys., 22, 3221-3229, 2004
www.ann-geophys.net/22/3221/2004/
© European Geosciences Union 2004
Longitudinal differences observed in the ionospheric F-region during the major geomagnetic storm of 31 March 2001
Y. Sahai1, P. R. Fagundes1, F. Becker-Guedes1, J. R. Abalde1, G. Crowley2, X. Pi3, K. Igarashi4, G. M. Amarante5, A. A. Pimenta6, and J. A. Bittencourt6
1Universidade do Vale do Paraiba (UNIVAP), 12244-000 São José dos Campos, SP, Brazil
2Southwest Research Institute, San Antonio, TX 78238-5166, USA
3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
4Communications Research Laboratory, Koganei-shi, Tokyo 184-8795, Japan
5The Abdus Salam ICTP, Strada Costeira 11, 34014 Trieste, Italy
6Instituto Nacional de Pesquisas Espaciais (INPE), 12201-970 São José dos Campos, SP, Brazil
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.
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