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| Titel |
Diurnal and seasonal occurrence of polar patches |
| VerfasserIn |
A. S. Rodger, A. C. Graham |
| 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 ; 14, no. 5 ; Nr. 14, no. 5, S.533-537 |
| Datensatznummer |
250012291
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| Publikation (Nr.) |
 copernicus.org/angeo-14-533-1996.pdf |
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| Zusammenfassung |
| Analysis of the diurnal and seasonal
variation of polar patches, as identified in two years of HF-radar data from
Halley, Antarctica during a period near sunspot maximum, shows that there is a
broad maximum in occurrence centred about magnetic noon, not local noon. There
are minima in occurrence near midsummer and midwinter, with maxima in occurrence
between equinox and winter. There are no significant correlations between the
occurrence of polar patches and the corresponding hourly averages of the solar
wind and IMF parameters, except that patches usually occur when the
interplanetary magnetic field has a southward component. The results can be
understood in terms of UT and seasonal differences in the plasma concentration
being convected from the dayside ionosphere into the polar cap. In summer and
winter the electron concentrations in the polar cap are high and low,
respectively, but relatively unstructured. About equinox, a tongue of enhanced
ionisation is convected into the polar cap; this tongue is then structured by
the effects of the interplanetary magnetic field, but these Halley data cannot
be used to separate the various competing mechanisms for patch formation. The
observed diurnal and seasonal variation in the occurrence of polar patches are
largely consistent with predictions of Sojka et al. (1994) when their
results are translated into the southern hemisphere. However, the ionospheric
effects of flux transfer events are still considered essential in their
formation, a feature not yet included in the Sojka et al. model. |
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