Unusual early morning development of the equatorial anomaly in the Brazilian sector during the Halloween magnetic storm

Abstract

[1] The solar events that occurred at the end of October 2003 gave rise to very strong geomagnetic disturbances that peaked twice with Dst values reaching À345 nT around 0000 UT on 30 October and À400 nT around 2300 UT, on the same day. Disturbances in several ionospheric parameters were observed over Brazil. This work will focus on the ionospheric response to the initial westward prompt penetration electric field and on the strong intensification of the equatorial ionization anomaly that occurred because of the electric field polarity reversal that followed in the early morning hours of 29 October. The F layer peak height over the equator first decreased under the strong prompt penetration westward electric field, which was followed by significant height increase under eastward electric field. We have used Sheffield University Plasmasphere Ionosphere Model (SUPIM) with an intensified westward disturbed electric field in the presunrise hours, presumably due to prompt penetration from the magnetosphere, in order to study the effect of such a field in the ionosphere. The simulation results showed that prompt penetration of magnetospheric electric fields of westward polarity to the nightside equatorial region seems to be the most probable cause of the initial F layer height decreases. The intensification of the equatorial ionization anomaly and the unusual enhancement on F layer peak density, which was not modeled by the SUPIM, are explained as caused by the strong eastward electric field that followed the initial phase in combination with a highly variable disturbed meridional/transequatorial wind system as inferred from the F2 layer peak height variations. The highly dynamic wind pattern, with a short-term response (2-4 hours), is compatible with the predictions of some previous theoretical model calculations reported in the literature.

The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003

“…The negative phase in the foF2 observations PAL and SJC are in accord with the depletions in GUVI O/N 2 ratio. features observed were spectacular uplifting of the F-region during pre-reversal time on both the nights of 29-30 and 30-31 October resulting in strong ESF, and unusual development of the equatorial ionospheric anomaly during early morning hours on 29 October (see also Batista et al, 2006). However, during the 20 November storm the unusual uplifting of the F-region was observed in the daytime and there was suppression of the pre-reversal enhancement with no ESF generation.…”

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

“…Several investigators Y. Sahai et al: Observations of the F-region ionospheric irregularities during "Halloween Storms" have studied the response of the ionospheric F-region in the equatorial and mid-latitude regions during the October 2003 Halloween storms (e.g., Basu et al, 2005Basu et al, , 2007Foster and Rideout, 2005;Lin et al, 2005;Zhao et al, 2005;Sahai et al, 2005;Yizengaw et al, 2005;Chi et al, 2005;Batista et al, 2006;Garner et al, 2006;Abdu et al, 2007Mannucci et al, 2008;Perevalova et al, 2008;Verkhoglyadova et al, 2008).…”

Effects of the midnight temperature maximum observed in the thermosphere–ionosphere over the northeast of Brazil

“…The ionosonde transmitter scans frequencies from 0.5 to 30 MHz with a peak power of 500 W. This instrument uses a crossed delta transmitting antenna and four crossed magnetic dipole receiving antennas (Reinisch et al, 1997;Batista et al, 2006). The DPS-4 basically operates vertically transmitting electromagnetic signals and measures the time lag until the echo is received.…”