Dependence of equatorial <i>F</i> region vertical drifts on season and solar cycle

Fejer, Bela G.; Farley, D. T.; Woodman, R. F.; Calderón, César

doi:10.1029/ja084ia10p05792

Cited by 323 publications

(182 citation statements)

References 26 publications

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“…These values remained above 0.29 Hz after 0953 UT, indicating the recovery and the strengthening of the eastward electric ®eld from 0950 UT in the E region which tracks the sharp increase in the H component at the equator from about 0830 UT. The occurrence of these irregularities subsequent to the disruption of the plasma drift pattern and the electron density distribution at equatorial latitude might suggest that the electric ®eld of high-latitude origin penetration event may be responsible for the triggering of these large-scale 3-m irregularity generations recorded on 27 May 1993 after 0950 UT, in agreement with Fejer and Kelley (1980), Fejer et al (1979a), and Fejer (1986.…”

Section: Ionospheric Electrodynamics Datasupporting

confidence: 66%

Equatorial electrojet as part of the global circuit: a case-study from the IEEY

Kobea

Amory‐Mazaudier²,

M.³

et al. 1998

Ann. Geophys.

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Abstract. Geomagnetic storm-time variations often occur coherently at high latitude and the day-side dip equator where they a ect the normal eastward Sq ®eld. This paper presents an analysis of ground magnetic ®eld and ionospheric electrodynamic data related to the geomagnetic storm which occured on 27 May 1993 during the International Equatorial Electrojet Year (IEEY) experiment. This storm-signature analysis on the auroral, mid-latitude and equatorial ground ®eld and ionospheric electrodynamic data leads to the identi®cat-ion of a sensitive response of the equatorial electrojet (EEJ) to large-scale auroral return current: this response consists in a change of the eastward electric ®eld during the pre-sunrise hours (0400±0600 UT) coherently to the high-, mid-, and equatorial-latitude H decrease and the disappearance of the EEJ irregularities between the timeinterval 0800±0950 UT. Subsequent to the change in h'F during pre-sunrise hours, the observed foF2 increase revealed an enhancement of the equatorial ionization anomaly (EIA) caused by the high-latitude penetrating electric ®eld. The strengthening of these irregularities attested by the Doppler frequency increase tracks the H component at the equator which undergoes a rapid increase around 0800 UT. The DH variations observed at the equator are the sum of the following components: S R , DP, DR, DCF and DT.

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Section: Ionospheric Electrodynamics Datasupporting

confidence: 66%

Equatorial electrojet as part of the global circuit: a case-study from the IEEY

Kobea

Amory‐Mazaudier²,

M.³

et al. 1998

Ann. Geophys.

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“…Further, near the magnetic equator, under normal conditions, the neutral wind dynamo also develops enhanced zonal electric field across the terminator because of the conductivity gradient as has been observed and modeled by several authors [Heelis et al, 1974;Farley et al, 1986;Fejer et al, 1979Fejer et al, , 2005. As such, at dusk, the eastward penetration electric field may add to the eastward electric field because of the neutral wind dynamo.…”

Section: Introductionmentioning

confidence: 87%

Response of the equatorial ionosphere at dusk to penetration electric fields during intense magnetic storms

et al. 2007

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different aspects of which have been widely studied by the community. We present here a very complete set of space and ground-based diagnostics that provide the vertical and latitudinal structures of the ionosphere within the South Atlantic magnetic anomaly (SAMA) region and the contiguous parts of South America and Africa. We show that for both storms, the dusk sector corresponding to the universal time (UT) interval between the fast decrease of the SYM-H index and minimum SYM-H value determines uniquely the longitude interval populated by equatorial plasma bubbles and depletions. Further, we find that the UT of these storms is such that the ionospheric density perturbations occur in the SAMA region, which are most extended in latitude and altitude compared with other regions of the globe. In the dusk sector, the eastward penetration electric field, associated with rapid SYM-H decrease, adds to the postsunset eastward E-field because of the F region dynamo, which may be specially enhanced in this longitude interval because of the increased zonal conductivity gradient caused by energetic particle precipitation. This enhanced E-field at dusk causes a rapid uplift of the ionosphere and sets off plasma instabilities to form bubbles or bite-outs. The decreased ion density seen in the Defense Meteorological Satellite Program (DMSP) in situ data at 840 km indicates that the ionospheric plasma has been lifted above the DMSP altitude and transported away from the region by diffusion along magnetic field lines. Plasma bubbles and bite-outs impact satellite communication and navigation systems by introducing scintillations and steep density gradients. This paper corroborates that intense magnetic storms follow the framework, developed by Su. Basu et al. (2001) for moderate storms, that specifies the longitude interval in which such disturbances are most likely to occur.

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“…It is well-known that the zonal electric field is westward at night (e.g., Fejer et al, 1979;Kelley, 1989) and there is no reason to think that the zonal electric field is changing sign at this time since such a trend does not show up in long-term averages except perhaps during summer solstice, solar minimum periods. We show some case studies later that show that the reversal does not occur.…”

Section: Simulations Of Post-midnight Upliftsmentioning

confidence: 99%

“…This relationship is due to the fact that the growth rate for the generalized RayleighTaylor instability is inversely proportional to the ion-neutral collision frequency, which decreases exponentially with altitude (Kelley et al, 1979a). A second term in the growth rate depends on the eastward electric field, which is destabilizing after F -region sunset and stabilizing during the night as dictated by the nominal F -region electric field driven by the dynamo wind systems (e.g., Fejer et al, 1979).…”

Section: Introductionmentioning

confidence: 99%

Observations and modeling of post-midnight uplifts near the magnetic equator

et al. 2006

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Abstract. We report here on post-midnight uplifts near the magnetic equator. We present observational evidence from digital ionosondes in Brazil, a digisonde in Peru, and other measurements at the Jicamarca Radio Observatory that show that these uplifts occur fairly regularly in the post-midnight period, raising the ionosphere by tens of kilometers in the most mild events and by over a hundred kilometers in the most severe events. We show that in general the uplifts are not the result of a zonal electric field reversal, and demonstrate instead that the uplifts occur as the ionospheric response to a decreasing westward electric field in conjunction with sufficient recombination and plasma flux. The decreasing westward electric field may be caused by a change in the wind system related to the midnight pressure bulge, which is associated with the midnight temperature maximum. In order to agree with observations from Jicamarca and Palmas, Brazil, it is shown that there must exist sufficient horizontal plasma flux associated with the pressure bulge. In addition, we show that the uplifts may be correlated with a secondary maximum in the spread-F occurrence rate in the post-midnight period. The uplifts are strongly seasonally dependent, presumably according to the seasonal dependence of the midnight pressure bulge, which leads to the necessary small westward field in the post-midnight period during certain seasons. We also discuss the enhancement of the uplifts associated with increased geomagnetic activity, which may be related to disturbance dynamo winds. Finally, we show that it is possible using simple numerical techniques to estimate the horizontal plasma flux and the vertical drift velocity from electron density measurements in the post-midnight period.

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Dependence of equatorial F region vertical drifts on season and solar cycle

Cited by 323 publications

References 26 publications

Equatorial electrojet as part of the global circuit: a case-study from the IEEY

Equatorial electrojet as part of the global circuit: a case-study from the IEEY

Response of the equatorial ionosphere at dusk to penetration electric fields during intense magnetic storms

Observations and modeling of post-midnight uplifts near the magnetic equator

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