Weather of the postsunset equatorial anomaly recorded daily during 2 years near solar maximum

The maximum F layer electron density of the postsunset equatorial anomaly is the location of the most disruptive scintillation to transionospheric L band transmissions when intersected by an equatorial bubble. Because bubble occurrence is essentially random, the anomaly is studied here for evidence...

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Veröffentlicht in:Space weather 2007-01, Vol.5 (1), p.np-n/a
1. Verfasser: Whalen, James A.
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Sprache:eng
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Zusammenfassung:The maximum F layer electron density of the postsunset equatorial anomaly is the location of the most disruptive scintillation to transionospheric L band transmissions when intersected by an equatorial bubble. Because bubble occurrence is essentially random, the anomaly is studied here for evidence of the predictability of the magnitude of its electron density and therefore of the magnitude of scintillation in the event of bubble occurrence. Measurements are by ionospheric sounders in the western American sector daily for 2 years during solar maximum. This first description of the weather of the anomaly for such an extended duration displays also the major climatological dependences on season and on solar flux, both of which reflect the dependence on the maximum prereversal E × B drift velocity. The most significant finding is that the anomaly electron density varies at intervals of a few days continuously throughout the entire 2 years. Within these intervals, maximum‐to‐minimum ratios are from 2 to ∼7 within overall magnitudes from 1 to ∼7 × 106 el/cm3. Although otherwise seemingly random, two extraordinary phenomena are evident. The first consists of extremely high magnitudes of electron density that recur for three solar rotations, the latitudinal profiles of which extend to midlatitudes and which are observed also in eastern Asia. The second, quasiperiodic variations of ∼3 days, appear nearly continuously also through three solar rotations. Evidence that both result from variations of the maximum prereversal E × B drift velocity indicates the presence of two contrasting mechanisms affecting drift velocity. The high magnitudes have not been observed before, but the quasiperiodic variations are similar to those observed in the daytime anomaly, where they are attributed to oscillations in the neutral mesosphere. Whatever the mechanism, recurrence of the magnitude of the anomaly indicates the possibility that it may be predicted, and therefore conditions may be predicted under which scintillation can occur.
ISSN:1542-7390
1542-7390
DOI:10.1029/2006SW000235