Seasonal and geomagnetic control of equatorial scintillations in two longitudinal sectors

Aarons, J.; Mullen, J. P.; Koster, J.P.; DaSilva, R.F.; Medeiros, Jéssica Ramalho de; Medeiros, R. T. de; Bushby, A. J.; Pantoja, J.; Lanat, J.; Paulson, M. R.

doi:10.1016/0021-9169(80)90090-2

Cited by 75 publications

(36 citation statements)

References 10 publications

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“…Any change in the electric field influences the occurrence of low-latitude scintillations. With increasing interest in understanding the behavior of ionospheric irregularities near the magnetic equator, efforts have been made to examine the influence of solar and magnetic activity over the occurrence of scintillations associated with ionospheric irregularities (Aarons et al, 1980;Rastogi et al, 1981;DasGupta et al, 1985;Dabas et al, 1989;Pathak et al, 1995;Chakraborty et al, 1999;Kumar and Gwal, 2000;Banola et al, 2001;Basu et al, 2001a, b;Bhattacharya et al, 2002). Analysis of the role of magnetic storms on low-latitude scintillations has shown that for most of the storms for which the recovery phase starts after midnight, the probability of occurrence of scintillation activity is enhanced during the post-midnight period (Aarons and Das Gupta, 1984;Kumar and Gwal, 2000).…”

Section: Introductionmentioning

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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Section: Introductionmentioning

confidence: 99%

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

2004

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“…Using the incoherent scatter radar observations at Jicamarca during geomagnetically disturbed periods, pointed out that anomalous reversals of electric fields from westward to eastward are accompanied by the increase of spread-F activity. The equatorial spread-F and scintillation activity in the morning local time shows strong correlation with Kp index (AARONS et al, 1980). BOWMAN (1975BOWMAN ( , 1978 pointed out the positive correlation between the bottomside spread-F occurrence in the postmidnight local time and the, geomagnetic activity, and suggested that this correlation may be attributable to the passage of TID produced by energy injection into the auroral region during substorms.…”

Section: Introductionmentioning

confidence: 97%

Ionospheric disturbances induced by substorm associated electric fields in the low-latitude F-region.

Takahashi¹,

Oya²,

Watanabe³

1987

J. geomagn. geoelec

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Based on the observation of low latitude ionosphere around 600 km altitude by the Hinotori satellite, well-defined signatures of the ionospheric disturbances associated with substorm activities are found. In the wide area of the nightside equatorial region, a remarkable enhancement of local electron density takes place in response to the enhancement of the AE index, with a time delay shorter than the revolution period of the satellite (97 min). The enhanced region is usually accompanied by several signatures which indicate the dynamical effects acting on the events, i.e. the development of the equatorial anomaly, longitudinal substructures and formation of the plasma bubbles. These signatures can be interpreted by dynamical uplift of the equatorial ionosphere. On the other hand, the equatorial anomaly is suppressed in dayside. Both of the nightside enhancement and the dayside suppression of the equatorial anomaly are induced simultaneously, although they are followed by rather different time sequential developments. The basic signatures of the ionospheric disturbance can be reasonably explained by dynamical effects of the disturbance electric field which is induced by substorm activities. The polarity of the disturbance electric field should be eastward in nightside and westward in dayside, and duration of the disturbance field is estimated to be about one hour or less.

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“…Such prediction can help to avoid blackouts and distortions in VLF communication due to ionospheric irregularities and can also help to advance the understanding of the nature of scintillations. The understanding of the variation of scintillation activity with solar epoch and seasons is well established by Koster (1972) and Aarons et al (1980). The scintillation activity during geomagnetic storms and disturbances is less well understood.…”

Section: Introductionmentioning

confidence: 99%

Role of the magnetospheric and ionospheric currents in the generation of the equatorial scintillations during geomagnetic storms

Biktash

2004

Ann. Geophys.

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Abstract. The equatorial ionosphere parameters, K p , D st , AU and AL indices characterized contribution of different magnetospheric and ionospheric currents to the Hcomponent of geomagnetic field are examined to test the geomagnetic activity effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict near 70% of scintillations from Aarons' criteria using the D st index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of electron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind -magnetosphere -ionosphere during magnetic storms have progressed greatly. According to present view, the intensity of the electric fields and currents at the polar regions, as well as the magnetospheric ring current intensity, are strongly dependent on the variations of the interplanetary magnetic field. The magnetospheric ring current cannot directly penetrate the equatorial ionosphere and because of this difficulties emerge in explaining its relation to scintillation activity. On the other hand, the equatorial scintillations can be observed in the absence of the magnetospheric ring current. It is shown that in addition to Aarons' criteria for the prediction of the ionospheric scintillations, models can be used to explain the relationship between the equatorial ionospheric parameters, h F , f oF 2, and the equatorial geomagnetic variations with the polar ionosphere currents and the solar wind.

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Seasonal and geomagnetic control of equatorial scintillations in two longitudinal sectors

Cited by 75 publications

References 10 publications

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

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

Ionospheric disturbances induced by substorm associated electric fields in the low-latitude F-region.

Role of the magnetospheric and ionospheric currents in the generation of the equatorial scintillations during geomagnetic storms

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