Response of nighttime equatorial and low latitude f-region to the geomagnetic storm of august 18, 2003, in the brazilian sector.

Resumo

This paper presents an investigation of geomagnetic storm effects in the equatorial and low latitude F-region in the Brazilian sector during the intense geomagnetic storm on 18 August 2003 (SSC 14:21 UT on 17/08; Kp=52+; Ap=108; |Dst|max=168 at 1600 UT on 18/08). Simultaneous ionospheric sounding measurements from two stations, viz., Palmas (10.2oS, 48.2oW; dip latitude 5.7oS) and Sao Jose dos Campos (23.2oS, 45.9oW; dip latitude 17.6oS), Brazil, are presented for the nights of 16-17, 17-18 and 18-19 August 2003 (quiet, disturbed and recovery phases). Both stations are equipped with the Canadian Advanced Digital Ionosonde (CADI). Quiet and disturbed conditions of the F-region ionosphere are compared using data collected from the two stations. The relationship between magnetospheric disturbance and low-latitude ionospheric dynamics, and generation of ionospheric irregularities are discussed. On the disturbed nights (17-18 and 18-19 August), the low latitude station S. J. Campos showed strong positive phase, whereas the near equatorial station Palmas showed strong uplifting of the F-layer. Normally during the June solstice months (May to August) in the Brazilian sector, large-scale ionospheric irregularities in form of plasma bubbles are rarely observed. On the night of 17-18 August, ionsospheric sounding observations at Palmas showed the presence of bottomside spread-F, whereas on the night of 18-19 August, the observations at Palmas and S. J. Campos showed the presence of plasma bubbles when the storm recovery phase had just started. The complementary GPS data available from several stations in the “Rede Brasileira de Monitoramento Continuo de GPS (Brazilian Network for Continuous GPS Monitoring)” are used to obtain the vertical total electron content (VTEC) and the rate of change of TEC per minute on UT days 18 and 19 August 2003 and presented. Also, several global ionospheric TEC maps from the worldwide network of GPS receivers are presented, showing widespread latitudinal and longitudinal TEC changes during the different phases of the storm. All the observations (local ionospheric sounding and GPS network measurements, and global GPS measurements) presented in this investigation related to the geomagnetic storm on 18 August indicate that the equatorial and low latitude region in the Brazilian sector underwent much stronger effect during the recovery phase compared with the main phase. (AU)