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| Titel |
The equatorial ionospheric anomaly in electron content from solar minimum to solar maximum for South East Asia |
| VerfasserIn |
G. O. Walker, J. H. K. Ma, E. Golton |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 12, no. 2/3 ; Nr. 12, no. 2/3, S.195-209 |
| Datensatznummer |
250010321
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| Publikation (Nr.) |
 copernicus.org/angeo-12-195-1994.pdf |
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| Zusammenfassung |
| Median hourly, electron content-latitude
profiles obtained in South East Asia under solar minimum and maximum conditions
have been used to establish seasonal and solar differences in the diurnal
variations of the ionospheric equatorial anomaly (EIA). The seasonal changes
have been mainly accounted for from a consideration of the daytime meridional
wind, affecting the EIA diffusion of ionization from the magnetic equator down
the magnetic field lines towards the crests. Depending upon the seasonal
location of the subsolar point in relation to the magnetic equator diffusion
rates were increased or decreased. This led to crest asymmetries at the
solstices with (1) the winter crest enhanced in the morning (increased diffusion
rate) and (2) the same crest decaying most rapidly in the late afternoon (faster
recombination rate at lower ionospheric levels). Such asymmetries were also
observed, to a lesser extent, at the equinoxes since the magnetic equator
(located at about 9°N lat) does not coincide with the geographic equator.
Another factor affecting the magnitude of a particular electron content crest
was the proximity of the subsolar point, since this increased the local
ionization production rate. Enhancements of the EIA took place around sunset,
mainly during the equinoxes and more frequently at solar maximum, and also there
was evidence of apparent EIA crest resurgences around 0300 LST for all seasons
at solar maximum. The latter are thought to be associated with the commonly
observed, post-midnight, ionization enhancements at midlatitudes, ionization
being transported to low latitudes by an equatorward wind. The ratio increases
in crest peak electron contents from solar minimum to maximum of 2.7 at the
equinoxes, 2.0 at the northern summer solstice and 1.7 at northern winter
solstice can be explained, only partly, by increases in the magnitude of the
eastward electric field E overhead the magnetic equator
affecting the [E×B] vertical drifts. The most
important factor is the corresponding increase in ionization production rate due
to the increase in solar radiation flux. The EIA crest asymmetries observed at
solar maximum were less significant, and this is probably due to the
corresponding increase in ionization densities leading to an increase of the
retarding effect of ion-drag on the daytime meridional winds. |
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