Response of the equatorial and low-latitude ionosphere during the space weather events of April 2002

W L C Lima,F Becker-Guedes,J R Abalde,Y Sahai,G Crowley,P R Fagundes,J A Bittencourt

doi:10.5194/angeo-22-3211-2004

Abstract

Abstract. A digital ionosonde, of the type known as Canadian Advanced Digital Ionosonde (CADI), has been in routine operation at São José dos Campos (23.2° S, 45.9° W; dip latitude 17.6° S), Brazil, since August 2000. A new CADI was installed at Palmas (10.2° S, 48.2° W; dip latitude 5.5° S), Brazil, in April 2002. The two CADIs are part of a new network being established in a collaborative program between UNIVAP and CEULP/ULBRA, to study the equatorial and low-latitude ionospheric regions in Brazil. In this paper we present and discuss the effects of the space weather events during 17-20 April 2002, as evidenced by the ionospheric parameter changes from simultaneous observations at São José dos Campos and Palmas. A comparison of the observed ionospheric parameters (h'F, hpF2 and foF2) at the two stations, separated only by about 1460km, shows both similarities and differences associated with the geomagnetic disturbances. Also, a comparison of the observed F-region parameters with the ASPEN-TIMEGCM model results is presented. The model results show reasonable agreement during the quiet period of observations, but some discrepancies have been observed during the geomagnetic disturbances.

Highlights

The studies related to space weather events are becoming increasingly important in the Sun-Earth system
During geomagnetic storms, which are extreme forms of space weather disturbances, the electric fields in the equatorial ionosphere could be primarily affected by two processes: 1) the solar wind-magnetosphere dynamo, associated with prompt or direct penetration of the magnetospheric convective electric field (e.g. Senior and Blanc, 1984; Spiro et al, 1988) and 2) the ionospheric disturbance dynamo, due to global thermospheric wind circulation associated with Joule heating at high latitude (e.g. Blanc and Richmond, 1980)
In this paper we present the simultaneous ionospheric sounding observations carried out at Palmas and Sao Josedos Campos, to investigate the response of the equatorial and low-latitude ionospheric regions during the space weather events which occurred in the period 16–20 April 2002

Summary

Introduction

The studies related to space weather events are becoming increasingly important in the Sun-Earth system. A new ionospheric sounding station equipped with a Canadian Advanced Digital Ionosonde (CADI) (Grant et al, 1995) was put in operation at Palmas (10.2◦ S, 48.2◦ W; dip latitude 5.5◦ S), in the equatorial region in Brazil, on 14 April 2002. Another ionospheric sounding station with a CADI was in routine operation at Sao Josedos Campos (23.2◦ S, 45.9◦ W; dip latitude 17.6◦ S), a low-latitude station in Brazil, since August 2000. The F -region parameters, obtained for the two ionospheric sounding stations, are compared with the model results (hourly values) generated by the Advanced SPace ENvironment (ASPEN)−Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM) (Crowley et al, 1999; see Roble and Ridley, 1994), for the period 16–20 April 2002

Observations

Results and discussions

Storm-time h F and f oF 2 variations

Positive phase

Observations and the ASPEN-TIMEGCM model results

Conclusions