Longitudinal differences observed in the ionospheric F-region during the major geomagnetic storm of 31 March 2001

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 Correspondence to: Y. Sahai (sahai@univap.br) 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.

Response of the ionosphere to super geomagnetic storms: Observations and modeling

“…At Wakanai (45.4°N geographic), there is a large but short-period decrease in hmF2 after the MP1 onset, which caused a small decrease in NmF2 before starting the positive ionospheric storm. Such short-period fluctuations (also in GPS-TEC, not shown) have been reported earlier and attributed to the fluctuations in neutral wind (e.g., Sahai et al, 2004). A positive ionospheric storm, though limited to low latitudes, is also observed on 10 November during the second super storm.…”

Relative effects of electric field and neutral wind on positive ionospheric storms

“…2). Such features have been observed earlier and attributed to the fluctuations in neutral wind (e.g., Sahai et al, 2004).…”

Optical observations of plasma bubble westward drifts over Brazilian tropical region

“…The energy of the storm that enters at high latitudes produces a disturbance in the thermospheric global circulation that, together with the Coriolis force, produce a wind for west (Richmond and Lu, 2000;Sahai et al, 2004). This phenomenon is very important for middle latitudes.…”