scholarly journals Longitudinal differences observed in the ionospheric F-region during the major geomagnetic storm of 31 March 2001

2004 ◽  
Vol 22 (9) ◽  
pp. 3221-3229 ◽  
Author(s):  
Y. Sahai ◽  
P. R. Fagundes ◽  
F. Becker-Guedes ◽  
J. R. Abalde ◽  
G. Crowley ◽  
...  
Keyword(s):  
Geomagnetic Storm ◽  
Recovery Period ◽  
Negative Phase ◽  
Quiet Period ◽  
Geomagnetic Disturbances ◽  
Low Latitude ◽  
F Region ◽  
Similarities And Differences ◽  
Worldwide Network ◽  
Ionospheric Sounding

Abstract. A new ionospheric sounding station using a Canadian Advanced Digital Ionosonde (CADI) was established for routine measurements by the "Universidade do Vale do Paraiba (UNIVAP)" at São José dos Campos (23.2° S, 45.9° W), Brazil, in August 2000. A major geomagnetic storm with gradual commencement at about 01:00 UT was observed on 31 March 2001. In this paper, we present and discuss salient features from the ionospheric sounding measurements carried out at S. J. Campos on the three consecutive UT days 30 March (quiet), 31 March (disturbed) and 1 April (recovery) 2001. During most of the storm period, the foF2 values showed negative phase, whereas during the two storm-time peaks, large F-region height variations were observed. In order to study the longitudinal differences observed in the F-region during the storm, the simultaneous ionospheric sounding measurements carried out at S. J. Campos, El Arenosillo (37.1° N, 6.7° W), Spain, Okinawa (26.3° N, 127.8° E), Japan and Wakkanai (45.5° N, 141.7° E), Japan, during the period 30 March-1 April 2001, have been analyzed. A comparison of the observed ionospheric parameters (h'F and foF2) in the two longitudinal zones (1. Japanese and 2. Brazilian-Spanish) shows both similarities and differences associated with the geomagnetic disturbances. Some latitudinal differences are also observed in the two longitudinal zones. In addition, global ionospheric TEC maps from the worldwide network of GPS receivers are presented, showing widespread TEC changes during both the main and recovery phases of the storm. The ionospheric sounding measurements are compared with the ASPEN-TIMEGCM model runs appropriate for the storm conditions. The model results produce better agreement during the quiet period. During the disturbed period, some of the observed F-region height variations are well reproduced by the model results. The model foF2 and TEC results differ considerably during the recovery period and indicate much stronger negative phase at all the stations, particularly at the low-latitude ones.

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

2004 ◽  
Vol 22 (9) ◽  
pp. 3211-3219 ◽  
Author(s):  
W. L. C. Lima ◽  
F. Becker-Guedes ◽  
Y. Sahai ◽  
P. R. Fagundes ◽  
J. R. Abalde ◽  
...  
Keyword(s):  
Space Weather ◽  
Reasonable Agreement ◽  
Quiet Period ◽  
Geomagnetic Disturbances ◽  
Low Latitude ◽  
F Region ◽  
Collaborative Program ◽  
Weather Events ◽  
Similarities And Differences ◽  
Low Latitude Ionosphere

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.

scholarly journals He<sup>+</sup> dominance in the plasmasphere during geomagnetically disturbed periods: 1. Observational results

2002 ◽  
Vol 20 (4) ◽  
pp. 461-470 ◽  
Author(s):  
M. H. Denton ◽  
G. J. Bailey ◽  
C. R. Wilford ◽  
A. S. Rodger ◽  
S. Venkatraman
Keyword(s):  
Geomagnetic Storm ◽  
Plasma Temperature ◽  
Recovery Phase ◽  
Geomagnetic Disturbance ◽  
Topside Ionosphere ◽  
Exchange Reactions ◽  
Geomagnetic Disturbances ◽  
Model Calculations ◽  
Flux Tubes ◽  
F Region

Abstract. Observations made by the DMSP F10 satellite during the recovery phase from geomagnetic disturbances in June 1991 show regions of He+ dominance around 830 km altitude at 09:00 MLT. These regions are co-located with a trough in ionisation observed around 55° in the winter hemisphere. Plasma temperature and concentration observations made during the severe geomagnetic storm of 24 March 1991 are used as a case study to determine the effects of geomagnetic disturbances along the orbit of the F10 satellite. Previous explanations for He+ dominance in this trough region relate to the part of the respective flux tubes that is in darkness. Such conditions are not relevant for this study, since the whole of the respective flux tubes are sunlit. A new mechanism is proposed to explain the He+ dominance in the trough region. This mechanism is based on plasma transport and chemical reaction effects in the F-region and topside ionosphere, and on the time scales for such chemical reactions. Flux tubes previously depleted by geomagnetic storm effects refill during the recovery phase from the ionosphere as a result of pressure differences along the flux tubes. Following a geomagnetic disturbance, the He+ ion recovers quickly via the rapid photoionisation of neutral helium, in the F-region and the topside. The recovery of the O+ and H+ ions is less rapid. This is proposed as a result of the respective charge exchange reactions with neutral atomic hydrogen and oxygen. Preliminary model calculations support the proposed mechanism.Key words. Magnetospheric physics (storms and sub-storms, plasmasphere)

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

2009 ◽  
Vol 27 (12) ◽  
pp. 4463-4477 ◽  
Author(s):  
Y. Sahai ◽  
F. Becker-Guedes ◽  
P. R. Fagundes ◽  
A. J. de Abreu ◽  
R. de Jesus ◽  
...  
Keyword(s):  
Geomagnetic Storms ◽  
Ionospheric Irregularities ◽  
South American ◽  
The South ◽  
Geomagnetic Disturbances ◽  
Plasma Bubbles ◽  
F Region ◽  
A Chain ◽  
Ionospheric Sounding ◽  
Gps Observations

Abstract. The response of the ionospheric F-region in the South American sector during the super geomagnetic storms on 29 and 30 October 2003 is studied in the present investigation. In this paper, we present ionospheric sounding observations during the period 29–31 October 2003 obtained at Palmas (a near equatorial location) and Sao Jose dos Campos (a location under the southern crest of the equatorial ionospheric anomaly), Brazil, along with observations during the period 27–31 October 2003 from a chain of GPS stations covering the South American sector from Imperatriz, Brazil, to Rio Grande, Argentina. Also, complementary observations that include sequences of all-sky images of the OI 777.4 and 630.0 nm emissions observed at El Leoncito, Argentina, on the nights of 28–29 (geomagnetically quiet night) and 29–30 (geomagnetically disturbed night) October 2003, and ion densities observed in the South American sector by the DMSP F13, F14 and F15 satellites orbiting at about 800 km on 29 and 30 October 2003 are presented. In addition, global TEC maps derived from GPS observations collected from the global GPS network of International GPS Service (IGS) are presented, showing widespread and drastic TEC changes during the different phases of the geomagnetic disturbances. The observations indicate that the equatorial ionospheric irregularities or plasma bubbles extend to the Argentinean station Rawson (geom. Lat. 33.1° S) and map at the magnetic equator at an altitude of about 2500 km.

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

2007 ◽  
Vol 39 (8) ◽  
pp. 1325-1334 ◽  
Author(s):  
Y. Sahai ◽  
F. Becker-Guedes ◽  
P.R. Fagundes ◽  
W.L.C. Lima ◽  
Y. Otsuka ◽  
...  
Keyword(s):  
Geomagnetic Storm ◽  
Low Latitude ◽  
F Region

Ionospheric response of equatorial and low latitude F-region during the intense geomagnetic storm on 24–25 August 2005

2012 ◽  
Vol 49 (3) ◽  
pp. 518-529 ◽  
Author(s):  
R. de Jesus ◽  
Y. Sahai ◽  
F.L. Guarnieri ◽  
P.R. Fagundes ◽  
A.J. de Abreu ◽  
...  
Keyword(s):  
Geomagnetic Storm ◽  
Low Latitude ◽  
Ionospheric Response ◽  
F Region

scholarly journals The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003

2007 ◽  
Vol 25 (4) ◽  
pp. 863-873 ◽  
Author(s):  
F. Becker-Guedes ◽  
Y. Sahai ◽  
P. R. Fagundes ◽  
E. S. Espinoza ◽  
V. G. Pillat ◽  
...  
Keyword(s):  
Geomagnetic Storm ◽  
Recovery Phase ◽  
Peak Height ◽  
Electron Content ◽  
Total Electron ◽  
Equatorial Station ◽  
Ionospheric Response ◽  
F Region ◽  
The Difference ◽  
Ionospheric Sounding

Abstract. A very intense geomagnetic storm (superstorm) began with storm sudden commencement (SSC) at 08:03 UT on 20 November 2003, as a result of the coronal mass ejection (CME) by sunspot 484 hurled into space on 18 November 2003. The geomagnetic storm attained |Dst|max=472 nT at 20:00 UT (20 November). In this paper we present the simultaneous ionospheric sounding observations, using the Canadian Advanced Digital Ionosondes (CADIs), carried out from Palmas (PAL; 10.2° S, 48.2° W; dip latitude 5.5° S; a near equatorial station) and São José dos Campos (SJC; 23.2° S, 45.9° W; dip latitude 17.6° S; station located under the crest of equatorial ionospheric anomaly), Brazil. In addition, total electron content (TEC) measurements from several GPS receiving stations in the Brazilian sector during this storm are presented. The simultaneous ionospheric sounding observations carried out at SJC and PAL, and TEC observations on 3 consecutive days viz., 19 November (quiet), 20 November (disturbed) and 21 November (recovery phase) are presented. Salient features from the ionospheric observations in the Brazilian sector during the superstorm are discussed. The difference in the observed ionospheric response at the two stations (PAL and SJC) is considerable. This is not surprising given that PAL is close to the magnetic equator and SJC is near the crest of the equatorial ionospheric anomaly (EIA). It should be pointed out that soon after the SSC (about 4 h later), the F-region critical frequency (foF2), the F-region peak height (hpF2), and variations of virtual heights at different frequencies (iso-frequency plots) all show wavelike oscillations of the F-region during daytime at both the ionospheric sounding stations. Unusual rapid uplifting of F-region at PAL was observed during both the main and recovery phases of the storm.

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