The equatorial ionospheric electric fields. A review

Fejer, Bela G.

doi:10.1016/0021-9169(81)90101-x

Cited by 194 publications

(109 citation statements)

References 54 publications

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“…In response to the diurnal variations of the dynamo electric field [Fejer, 1981], the anomaly crest begins to form around 09:00 LT on a normal day. As time progresses, the anomaly crest intensifies and moves with a speed of about 1ø per hour to a higher latitude.…”

Section: Resultsmentioning

confidence: 99%

An investigation of motions of the equatorial anomaly crest

Yeh

Franke

Andreeva

et al. 2001

Geophysical Research Letters

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Abstract.Using more than 350 ionospheric images reconstructed tomographically, studies on the motion of the anomaly crest and its geophysical implications are carried out. On an average day, the crest forms at 09:00 LT and,,in the next two hours, moves poleward with a speed of about 1 ø per hour as it intensifies. This poleward motion is slowed as the crest reaches its highest latitude where it stays for several hours until early afternoon. Thereafter, the crest starts to weaken as it recedes with a speed of about 0.5 ø per hour equatorward. During 12:00-14:00 LT, the crest latitude is found to correlate with the fountain strength and the total number of electrons in a cross sectional plane at the observational longitude of the whole equatorial ionosphere.

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Section: Resultsmentioning

confidence: 99%

An investigation of motions of the equatorial anomaly crest

Yeh

Franke

Andreeva

et al. 2001

Geophysical Research Letters

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“…In this case, the average low solar flux indices were ~75; the high solar flux values were ~195 for June solstice and equinox, and 174 for December solstice. The evening upward and the nighttime downward drifts have small average values and are also highly variable for all seasons near solar minimum [e.g., Fejer, 1981]. In this case, spread F can be easily excited whenever the drift velocities after sunset are upward for periods longer than about half an hour due to either their quiet time variability or to upward disturbance drifts.…”

Section: Spread F During Premidnight Hoursmentioning

confidence: 99%

Effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread F

Fejer¹,

Scherliess²,

Paula³

1999

J. Geophys. Res.

650

754

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Abstract. We use radar observations from the Jicamarca Observatory from 1968 to 1992 to study the effects of the F region vertical plasma drift velocity on the generation and evolution of equatorial spread F. The dependence of these irregularities on season, solar cycle, and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts. In the early night sector, the bottomside of the F layer is almost always unstable. The evolution of the unstable layer is controlled by the history of the vertical drift velocity. When the drift velocities are large enough, the necessary seeding mechanisms for the generation of strong spread F always appear to be present. The threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux. The geomagnetic control on the generation of spread F is season, solar cycle, and longitude dependent. These effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields. The occurrence of early night spread F decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset. The generation of late night spread F requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour. These irregularities occur most often at -0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes. The occurrence of late night spread F is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux.

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“…This is in agreement with the observations of Banola et al (2001) for the same magnetic storm at the equatorial station Trivandrum. During D st excursions in the pre-midnight period, the eastward electric field is enhanced and consequently, the F-layer along with the irregularities formed at the bottom of the F-layer are lifted upwards (Fejer, 1981;Banola et al, 2001). …”

Section: Examples Of Category-iiimentioning

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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The equatorial ionospheric electric fields. A review

Cited by 194 publications

References 54 publications

An investigation of motions of the equatorial anomaly crest

An investigation of motions of the equatorial anomaly crest

Effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread F

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

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