Ionospheric storm of early November 1993 in the Indian equatorial region

Sastri, J. H.; Jyoti, N.; Somayajulu, V. V.; Chandra, H.; Devasia, C. V.

doi:10.1029/1999ja000372

Cited by 83 publications

(65 citation statements)

References 45 publications

(19 reference statements)

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“…It follows from the results of Fesen et al (1989) that the equatorial anomaly may be disrupted by the magnetic storm, and the major factor influencing the storm-time ionospheric behavior is the neutral wind. This point of view was reiterated in recent studies, for example, by Sastri et al (2000), with particular reference to the wellknown storm in early November 1993. The coupled thermosphere ionosphere plasmasphere electrodynamic model was used by Fuller-Rowell et al (2002) to model the low-latitude ionosphere and plasmasphere for a hypothetical geomagnetic storm at equinox and high solar activity without taking into account geomagnetic storm disturbances in an electric field.…”

Section: Introductionmentioning

confidence: 91%

<i>F</i>-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

2004

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Abstract.We have presented a comparison between the modeled N mF 2 and hmF 2, and N mF 2 and hmF 2 which were observed at the equatorial anomaly crest and close to the geomagnetic equator simultaneously by the Akita, Kokubunji, Yamagawa, Okinawa, Manila, Vanimo, and Darwin ionospheric sounders and by the middle and upper atmosphere (MU) radar (34.85 • N, 136.10 • E) during the 25-27 August 1987 geomagnetically storm-time period at low solar activity near 201 • , geomagnetic longitude. A comparison between the electron and ion temperatures measured by the MU radar and those produced by the model of the ionosphere and plasmasphere is presented. The corrections of the storm-time zonal electric field, E , from 16:30 UT to 21:00 UT on 25 August bring the modeled and measured hmF 2 into reasonable agreement. In both hemispheres, the meridional neutral wind, W, taken from the HWW90 wind model and the NRLMSISE-00 neutral temperature, T n , and densities are corrected so that the model results agree with the ionospheric sounders and MU radar observations. The geomagnetic latitude variations in N mF 2 on 26 August differ significantly from those on 25 and 27 August. The equatorial plasma fountain undergoes significant inhibition on 26 August. This suppression of the equatorial anomaly on 26 August is not due to a reduction in the meridional component of the plasma drift perpendicular to the geomagnetic field direction, but is due to the action of storm-time changes in neutral winds and densities on the plasma fountain process. The asymmetry in W determines most of the northsouth asymmetry in hmF 2 and N mF 2 on 25 and 27 August between about 01:00-01:30 UT and about 14:00 UT when the equatorial anomaly exists in the ionosphere, while asymmetries in W, T n , and neutral densities relative to the geomagnetic equator are responsible for the north-south asymmetry in N mF 2 and hmF 2 on 26 August. A theory of the primary mechanisms causing the morning and evening peaks in the electron temperature, T e , is developed. An appearCorrespondence to: A. V. Pavlov (pavlov@izmiran.rssi.ru) ance, magnitude variations, latitude variations, and a disappearance of the morning T e peaks during 25-27 August are caused by variations in E , thermospheric composition, T n , and W. The magnitude of the evening T e peak and its time location are decreased with the lowering of the geomagnetic latitude due to the weakening of the effect of the plasma drift caused by W on the electron density. The difference between 25 August and 26-27 August in an appearance, magnitude and latitude variations, and a disappearance of the evening T e peak is caused by variations in W, the thermospheric composition, T n , and E .

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Section: Introductionmentioning

confidence: 91%

<i>F</i>-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

2004

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“…Such a situation may create irregularities and this might be the cause of scintillations during midnight and post-midnight periods. Sastri et al (2000) have suggested that, even in the presence of favorable conditions, like an eastward electric field, some as yet unidentifiable factors may suppress the generation of fresh irregularities in the post-midnight period. Using the measurements of thermospheric neutral wind and irregularities drift, Valladares et al (2002) have investigated the coupling between ions and neutrals at the equatorial latitudes.…”

Section: Effect Of Magnetic Activitymentioning

confidence: 99%

Effect of solar and magnetic activity on VHF scintillations near the equatorial anomaly crest

2004

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Abstract. The VHF amplitude scintillation recorded during the period January 1991 to December 1993 in the declining phase of a solar cycle and April 1998 to December 1999 in the ascending phase of the next solar cycle at Varanasi (geogr. lat.=25.3 • , long. =83.0 • , dip=37 • N) have been analyzed to study the behavior of ionospheric irregularities during active solar periods and magnetic storms. It is shown that irregularities occur at arbitrary times and may last for <30 min. A rise in solar activity increases scintillations during winter (November-February) and near equinoxes (March-April; September-October), whereas it depresses the scintillations during the summer (May-July). In general, the role of magnetic activity is to suppress scintillations in the pre-midnight period and to increase it in the post-midnight period during equinox and winter seasons, whilst during summer months the effect is reversed. The pre-midnight scintillation is sometimes observed when the main phase of D st corresponds to the pre-midnight period. The annual variation shows suppression of scintillations on disturbed days, both during premidnight and post-midnight period, which becomes more effective during years of high solar activity. It is observed that for magnetic storms for which the recovery phase starts postmidnight, the probability of occurrence of irregularities is enhanced during this time. If the magnetic storm occurred during daytime, then the probability of occurrence of scintillations during the night hours is decreased. The penetration of magnetospheric electric fields to the magnetic equator affects the evolution of low-latitude irregularities. A delayed disturbance dynamo electric field also affects the development of irregularities.

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“…∼600 m/s) in meridional direction. It has been emphasized that AGWs affect the ionosphere primarily through their meridional winds, which drag the ionization along the inclined magnetic field lines (Kirchengast et al, 1996;Sastri et al, 2000). The height of the ionization layer is thus changed and an increase in layer height leads to a positive ionospheric storm if the height dependence of ionization production and loss is considered.…”

Section: Introductionmentioning

confidence: 99%

Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone

Dashora

Sharma²,

Dabas

et al. 2009

Ann. Geophys.

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Abstract.Results pertaining to the response of the equatorial and low latitude ionosphere to a major geomagnetic storm that occurred on 15 May 2005 are presented. These results are also the first from the Indian zone in terms of (i) GPS derived total electron content (TEC) variations following the storm (ii) Local low latitude electrodynamics response to penetration of high latitude convection electric field (iii) effect of storm induced traveling atmospheric disturbances (TAD's) on GPS-TEC in equatorial ionization anomaly (EIA) zone.

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Ionospheric storm of early November 1993 in the Indian equatorial region

Cited by 83 publications

References 45 publications

<i>F</i>-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

<i>F</i>-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

Effect of solar and magnetic activity on VHF scintillations near the equatorial anomaly crest

Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone

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Ionospheric storm of early November 1993 in the Indian equatorial region

Cited by 83 publications

References 45 publications

&lt;i&gt;F&lt;/i&gt;-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

&lt;i&gt;F&lt;/i&gt;-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

Effect of solar and magnetic activity on VHF scintillations near the equatorial anomaly crest

Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone

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<i>F</i>-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

<i>F</i>-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987