Geomagnetic storm and equatorial spread-F

Abstract

Abstract. In August 2000, a new ionospheric sounding station was established at Sao Jose dos Campos (23.2° S, 45.9° W; dip latitude 17.6° S), Brazil, by the University of Vale do Paraiba (UNIVAP). Another ionospheric sounding station was established at Palmas (10.2° S, 48.2° W; dip latitude 5.5° S), Brazil, in April 2002, by UNIVAP in collaboration with the Lutheran University Center of Palmas (CEULP), Lutheran University of Brazil (ULBRA). Both the stations are equipped with digital ionosonde of the type known as Canadian Advanced Digital Ionosonde (CADI). In order to study the effects of geomagnetic storms on equatorial spread-F, we present and discuss three case studies, two from the ionospheric sounding observations at Sao Jose dos Campos (September and November 2000) and one from the simultaneous ionospheric sounding observations at Sao Jose dos Campos and Palmas (July 2003). Salient features from these ionospheric observations are presented and discussed in this paper. It has been observed that sometimes (e.g. 4-5 November 2000) the geomagnetic storm acts as an inhibitor (high strong spread-F season), whereas at other times (e.g. 11-12 July 2003) they act as an initiator (low strong spread-F season), possibly due to corresponding changes in the quiet and disturbed drift patterns during different seasons.

Role of overshielding electric field on the development of pre-midnight plume event: Simulation results

“…It is to be noted that since the scattering of radio waves, in general, occurs above the base of the F layer, temporal variations in h'F can be used to derive plasma drifts even during ESF condition as followed by many researchers (e.g. Subbarao and Krishna Murthy, 1994;Becker-Guedes et al, 2004). Reversals from downward to upward plasma drifts corresponding to the zonal electric fields are observed just after 2000 and 2145 IST.…”

Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 "Halloween Storms"

“…Of the late, the earlier view that a geomagnetic storm suppresses the generation of the ESF is no longer valid (e.g., Tsurutani et al, 2004;Becker-Guedes et al, 2004;Martinis et al, 2005;Chakrabarty et al, 2006). However, several investigators have reported ESF in post midnight period during geomagnetic disturbances earlier.…”

The statistical properties of spread F observed at Hainan station during the declining period of the 23rd solar cycle

“…Their morphological characteristics at different longitudes of equatorial latitudes has been described as a function of spatial, temporal, solar cycle and magnetic activity variations (Aarons, 1993;Abdu et al, 1981Abdu et al, , 1985Abdu et al, , 1992Cragin et al, 1985;Kil and Heelis, 1998). Recently several investigators have reported SF properties and ionospheric response during superstorm times (Becker-Guedes, 2004;Sahai et al, 2005;Abdu et al, 2007).…”