Response of nighttime equatorial and low latitude F-region to the geomagnetic storm of August 18, 2003, in the Brazilian sector

doi:10.1016/j.asr.2007.02.064

Advances in Space Research

Volume 39, Issue 8, 2007, Pages 1325-1334

https://doi.org/10.1016/j.asr.2007.02.064 Get rights and content

Abstract

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; ΣKp = 52+; Ap = 108; ∣Dst∣_max = 168 at 1600 UT on 18/08). Simultaneous ionospheric sounding measurements from two stations, viz., Palmas (10.2°S, 48.2°W; dip latitude 5.7°S) and Sao Jose dos Campos (23.2°S, 45.9°W; dip latitude 17.6°S), 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 enhancements in the F-region critical frequency (foF2), whereas the near equatorial station Palmas showed strong uplifting of the F-layer about 1 h earlier. Normally during the June solstice months (May–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 had much stronger effect during the recovery phase compared with the main phase. A comparison of the observed disturbance drifts with the Fejer–Scherliess storm-time model drifts indicate that the modeled drifts are not consistent with the present observations.

Introduction

The response of equatorial ionosphere–thermosphere system during geomagnetic disturbances is one of the important issues in space weather studies and has been the subject of several investigations during the recent years (see e.g., Sahai et al., 2005 and the references cited). Simultaneous ionospheric sounding measurements from two stations, viz., Palmas (10.2°S, 48.2°W; dip latitude 5.7°S; hereafter referred as PAL) and Sao Jose dos Campos (23.2°S, 45.9°W; dip latitude 17.6°S; hereafter referred as SJC), Brazil, are presented for three nights (1500–0900 LT), viz., 16–17, 17–18 and 18–19 August, 2003. The period selected for the present study relates to geomagnetic storm effects on the nighttime equatorial and low latitude F-region during the intense geomagnetic storm of 17–18 August, 2003. The storm started with a sudden commencement at 1421 UT on 17 August and Dst reached −168 nT (maximum drop of this storm) at 1600 UT on 18 August (ΣKp = 52+; Ap = 108), followed by the recovery phase. It should be pointed out that the storm of 17–18 August, 2003, had a fairly broad main phase. In this paper, a comparative study of the ionospheric data from the two stations in the Brazilian sector for the quiet (16–17 August), disturbed and recovery phases (17–18 and 18–19 August) are presented and discussed in terms of magnetospheric disturbance related changes in the nighttime F-region heights, electron densities and generation of ionospheric irregularities (equatorial spread-F (ESF)) in the equatorial and low latitude regions. The generation/suppression of ESF during magnetic disturbances is an important subject to the space weather community due to its impact on the satellite communication and has been recently investigated by several workers (e.g., Sahai et al., 1998, Palmroth et al., 2000, Whalen, 2002, Bhattacharya et al., 2002, Abdu et al., 2003, Becker-Guedes et al., 2004, Martinis et al., 2005). Also, the F-region changes observed during the geomagnetic storm are compared with the complementary GPS data available from several stations (Table 1) in the “Rede Brasileira de Monitoramento Continuo de GPS (Brazilian Network for Continuous GPS Monitoring)”. The GPS data 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.

Fig. 1 presents the universal time variations of the Kp (3-hourly values), Dst (hourly values) and AE (obtained from the website – http://swdcdb.kugi.kyoto-u.ac.jp/wdc/Sec3.html) geomagnetic indices for the period 17–19 August, 2003. The interplanetary magnetic field (IMF) Bz component values (obtained from the website – http://www.srl.caltech.edu/ACE/ASC/) are also shown in Fig. 1. The AE index is important for providing information related to the occurrence and intensity of substorms. Also, the AE values of the order of 500 nT are fairly common (Akasofu, 1970). Fig. 1 shows that after the SSC at 1421 UT (17/08), the AE index had a quick rise to about 750 nT at about 1700 UT and then the AE index remained disturbed up to about 0400 UT on 19 August. The AE values during this disturbed period fluctuated between 500 nT and 1700 nT, indicating a fairly extended period of polar disturbances (Davis and Sugiura, 1968). Also, Fig. 1 shows the magnetic field (H-component) variations observed at the Magnetic Observatory of Vassouras (22.4°S, 34.6°W; dip latitude 18.5°S), Brazil. The H-component variations shown in Fig. 1 (every minute values) were obtained after subtracting the quiet day H-Component variations observed on 16 August and represent the storm-time variations. The increase (a positive bay) in the H-component variations during the main phase of the storm at Vassouras, a low-latitude station, is possibly associated with the auroral substorms (Shiokawa et al., 2000, Huang et al., 2004). The hatched portions in Fig. 1, indicate the local night period (1800–0600 LT) in the Brazilian sector.

Section snippets

Observations

In this paper we present ionospheric sounding data (F-region critical frequency (foF2), minimum F-region virtual height (h’F) and virtual height at 0.834foF2 (hpF2; at nighttime hpF2 ≈ hmF2 (see e.g. Danilov and Morozova, 1985)) obtained (every 15 min) at the two stations (PAL and SJC) on the nights of 16–17, 17–18 and 18–19 August, 2003. As mentioned earlier the nights selected include quiet (16–17 August), geomagnetically disturbed and recovery phases (17–18 and 18–19 August). It should be

Results and discussion

Even during geomagnetically quiet conditions, the nighttime ionospheric F-region shows relatively small day-to-day variability associated with both the plasma and neutral dynamics (e.g., Fagundes et al., 1999, Mendillo et al., 2001). However, during the storm conditions, the F-region in the equatorial and low latitude sectors undergoes much more pronounced changes sometimes both in the F-region height and peak electron density. These changes are associated with the solar wind-magnetosphere

Conclusions

In this paper, we have analyzed and presented the simultaneous ionospheric sounding observations carried out in the Brazilian sector at PAL and SJC during the intense geo-magnetic storm on August 18, 2003. The storm had a very broad main phase after the SSC. The main results are as follows:

1.
The near equatorial station PAL showed large F-region height changes on both the nights (17–18 and 18–19 August, 2003) during the main and recovery phases, though variations of the F-region peak electron

Acknowledgements

We convey our grateful thanks to the authorities of the “Rede Brasileira de Monitoramento Continuo de GPS” for kindly allowing us to use the GPS data obtained by RBMC and Ronaldo Marins de Carvalho, Observatorio Nacional, Rio de Janeiro, for kindly providing the magnetometer observations carried out at Vassouras, Brazil. Thanks are due to Dr. Carlos Martinis for kindly providing the Fejer–Scherliess storm-time drift model results and several helpful discussions. The research conducted at the

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Response of nighttime equatorial and low latitude F-region to the geomagnetic storm of August 18, 2003, in the Brazilian sector

Abstract

Introduction

Section snippets

Observations

Results and discussion

Conclusions

Acknowledgements

J. Atmos. Solar-Terr. Phys.

J. Atmosp. Sol. Terr. Phys.

J. Atmos. Terr. Phys.

Observations of equatorial F region plasma bubbles using simultaneous OI 777.4 nm and OI 630.0 nm imaging: new results

J. Geophys. Res.

Magnetospheric disturbance induced equatorial plasma bubble development and dynamics: a case study in the Brazilian sector

J. Geophys. Res.

Diagnostics of the magnetosphere using geomagnetic, auroral and airglow phenomena

Ann. Geophys.

Response of the equatorial ionosphere in the South Atlantic region to the great magnetic storm of July 15, 2000

Geophys. Res. Lett.

Equatorial ionization vertical plasma drift model over the Brazilian region

J. Geophys. Res.

Geomagnetic storms and equatorial spread-F

Ann. Geophys.

Effect of magnetic activity on the dynamics of equatorial F region irregularities

J. Geophys. Res.

The ionospheric disturbance dynamo

J. Geophys. Res.

Ionospheric storms – a review

Space Sci. Rev.

The equatorial neutral thermospheric response to geomagnetic forcing

Geophys. Res. Lett.

Ionospheric storms in the F2 region. Morphology and Physics (review)

Geomag. Aeron.

Auroral electrojet activity index AE and its universal time variations

J. Geophys. Res.

Observation of day-to-day variability in precursor signatures to equatorial F-region plasma depletions

Ann. Geophys.

Empirical models of storm time equatorial zonal electric fields

J. Geophys. Res.

Ionospheric storms in the F₂ region. Morphology and Physics (review)