Ionospheric response to a geomagnetic storm during November 8–10, 2004

K G Simi,G Manju,S Alex,Tarun Kumar Pant,M K Madhav Haridas,S R Prabhakaran Nayar

doi:10.5047/eps.2012.09.005

Abstract

This paper investigates the response of the equatorial, and near equatorial, ionosphere to geomagnetic disturbances during the period November 8–10, 2004. Ionosonde data from Trivandrum (8.5°N 77°E and dip 0.5°N) and SHAR (13.5°N, 80.2°E, dip ~5.5°N), magnetic field data from Tirunelveli (8.7°N, 76.9°E, dip latitude 0.5°S) and Alibag (18.64°N, 72.87°E), and GUVI O/N2 data in the Indian longitude sector, are used for the study. The behavior of interplanetary parameters is also examined in conjunction with the ionospheric data. On 8 November, the EIA around noontime is not fully inhibited even though the electrojet strength an indicates inhibition of EIA due to a disturbance dynamo electric field effect. It is the enhanced O/N2 over TRV and SHAR, with a larger increase over SHAR, which results in a larger (than expected) value of the EIA proxy parameter. On 9 November, the comparable values of foF2 at TRV and SHAR around noon time is due to the combined effect of a weakened anomaly in the presence disturbance dynamo electric field effects leading to the EIA crest being near SHAR, and increased O/N2 values at TRV and SHAR with a larger increase at TRV. On 10 November, the very strong values of the EIA proxy-SHAR parameter is attributed to the combined effects of prompt penetration electric field related modulations of EIA, and significant O/N2 changes at the equatorial, and near equatorial, latitude. Thus, the study reveals the important role of storm-induced O/N2 changes, along with prompt penetration electric fields and disturbance dynamo electric fields in modulating the ionization distribution in the equatorial ionization anomaly (EIA) region during this period.

Highlights

The ionospheric response to changes in solar wind conditions has been the subject of intense study for many years (Blanc and Richmond, 1980; Fuller-Rowell et al, 1997; Prolss, 1997; Buonsanto, 1999; Richmond and Lu, 2000)
From solar wind data available from the Advanced Composition Explorer (ACE) satellite, coronal mass ejection effects were evident during 7–10 November as the solar wind velocity increased from 420 to 660 km/s, particle densities increased to 27 cm−3, and Bz became strongly southward
A minimum value of −363 nT at around 1000 IST. This period is marked as the main phase of the storm. This is followed by a recovery phase, as is evident from the SYM (H) index and interplanetary magnetic field (IMF) Bz .The AE index (Fig. 1(b)) exhibits a peak of 2189 nT around this time. 3.2 Response of O/N2 at TRV and SHAR for the storm period viz-a-viz the control day pattern Figure 2 depicts the O/N2 values for 8, 9 and 10 November, 2004, along with the control day pattern for 6 November, 2004

Summary

Introduction

The ionospheric response to changes in solar wind conditions has been the subject of intense study for many years (Blanc and Richmond, 1980; Fuller-Rowell et al, 1997; Prolss, 1997; Buonsanto, 1999; Richmond and Lu, 2000). Fejer et al (2007) studied the electric fields over equatorial ionosphere during the November 7–9, 2004, geomagnetic storm, using radar measurements from the Jicamarca Radio Observatory, magnetometer observations from the Pacific sector and ionosonde data from Brazil They showed very large eastward and westward daytime electrojet current perturbations with lifetimes of about an hour (indicative of undershielding and overshielding prompt penetration electric fields) in the Pacific equatorial region during November 7, which was the main phase of the storm. Their results highlight that the relationships between prompt penetration, solar wind electric fields, and polar cap potentials, are far more complex than implied by simple proportionality factors. For SHAR, the O/N2 value is obtained by averaging the values over the region 11.5◦N–15.5◦N and 75◦E–85◦E

Interplanetary measurements

Discussion

Conclusion