Effects of the major geomagnetic storms of October 2003 on the equatorial and low‐latitude F region in two longitudinal sectors

Abstract

[1] The intense modifications in the ionosphere-thermosphere system in the equatorial and low-latitude regions associated with the dynamic and electrodynamic coupling from high to low latitudes and chemical changes during geomagnetic storms are important space weather issues. In the second half of October 2003, the intense solar activity resulted in one intense and two major geomagnetic storms on 29 and 30 October. In this paper we present and discuss the ionospheric sounding observations carried out from Palmas and São José dos Campos, Brazil (the Brazilian sector), and Ho Chi Minh City, Vietnam, and Okinawa, Japan (the East Asian sector), during these storms. The two sectors are separated by about 12 hours in local time (so while one sector is in daytime, the other one is in nighttime) and provide valuable information related to the storm-time longitudinal differences. Copious storm-time changes were observed in both sectors. It should be pointed out that the two longitudinal sectors investigated in the present study clearly show the global nature of the storm-time effects. However, the responses to the storm-time effects are also associated with the local time in the two sectors. The present investigations show that there are both similarities and differences in the storm-time response in the two sectors. During the storm main phases, with sharp decreases of the Dst index, both sectors showed (dusk or dawn periods) fast uplifting of the F layer associated with magnetospheric electric field penetration. Although in the East Asian sector, Ho Chi Minh City and Okinawa are located fairly close in longitude, with only 2 hour difference in local lime, on occasions the storm-time responses have been very different. Some differences in the latitudinal response of the F region were also observed in the two sectors. Both positive and negative storm phases have been observed at all the four stations. A comparison of the ionospheric parameters obtained from the TIMEGCM model runs and the observed ionospheric parameters at the four stations shows a reasonable agreement during the quiet periods. During the geomagnetic disturbance period, when there were sharp decreases in Dst, some of the observed rapid uplifts of the F region peak heights are not reproduced by the model results. Also, sometimes the model foF2 results differ considerably from the observed foF2 variations. The period investigated represents an extreme storm situation for validation of the model and points to ways in which the model might be improved in the future.

Response of the equatorial ionosphere at dusk to penetration electric fields during intense magnetic storms

“…It illustrates the variations of the critical frequency (foF2), minimum virtual height (h 0 F), and the virtual height at 0.8 foF2 (h p F2) of the F region [Sahai et al, 2005]. In conformity with the DMSP data shown in Figure 8d, the ionosonde measurements indicate much enhanced critical frequency, foF2, at 20 LT as high as 10 MHz at the equator and 15 MHz over the southern crest of the anomaly at SJC.…”

Oxygen ion uplift and satellite drag effects during the 30 October 2003 daytime superfountain event

“…Recently, promptly penetrating electric fields (PPEFs) associated with major IEF events have been discovered to last more than several hours at ionospheric heights (Tsurutani et al, 2004;Maruyama et al, 2004;Mannucci et al, 2005;Sahai et al, 2005;Huang et al, 2005). When these electric fields are intense and are in the dawnto-dusk (eastward if viewed from the Northern Hemisphere)…”

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

“…As described by Gopalswamy et al (2005) the solar-terrestrial events of late October and early November 2003, popularly referred as the Halloween storms, represent the best observed cases of extreme space weather activity observed to date and have generated research covering multiple aspects of solar eruptions and their space weather effects. and Sahai et al (2005) have mentioned that on 28 and 29 October launch of fast coronal mass ejections (CMEs) were associated with the solar flares and their impacts on the Earth's magnetosphere resulted in major geomagnetic storms on 29 and 30 October (Halloween storms). The geomagnetic storms on the 29 and 30 October (and their interplanetary causes) were discussed in greater detail by Wu et al (2005) and Mannucci et al (2005).…”

“…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).…”