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

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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
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