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| Titel |
Relation between the occurrence rate of ESF and the equatorial vertical plasma drift velocity at sunset derived from global observations |
| VerfasserIn |
C. Stolle, H. Lühr, B. G. Fejer |
| 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 ; 26, no. 12 ; Nr. 26, no. 12 (2008-12-08), S.3979-3988 |
| Datensatznummer |
250016324
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| Publikation (Nr.) |
 copernicus.org/angeo-26-3979-2008.pdf |
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| Zusammenfassung |
In this study, we investigate two global
climatological data sets; the occurrence rate of Equatorial Spread-F
(ESF), associated with
equatorial plasma irregularities,
at ~400 km altitude
obtained from CHAMP observations, and the evening
equatorial vertical plasma drift, vz,
from ROCSAT-1 measurements.
First, as retrieved for a solar flux level of F10.7=150,
the longitudinal variation of the two independently derived
quantities correlates between 84% and 93%
in the seasons December solstice, equinox and June solstice.
The highest correlation is found for the solstice seasons
when vz is integrated over local time
around the prereversal enhancement (PRE) and displaced
6° towards east.
The integrated vz is a suitable estimate of the ionospheric height
at the time just after the PRE and the 6°
displacement is consistent with ESF eastward drift during
2 h which is assumed between creation and detection at satellite altitudes.
Second, our analyses reveal a global threshold vz which is required to
observe ESF at satellite altitudes. This threshold depends linearly
on solar flux with correlations of 97%.
Both results bring global evidence on the linear relations between ESF
and the vertical plasma drift
which have been proven only by local observations
so far.
This paper includes the first global map of the
seasonal/longitudinal variation of the ESF occurrence rate over
local time being valid for high solar flux years 2001–2004.
The map reveals, e.g. a longitudinal dependence of the persistence of the
plasma irregularities
indicating that longitude dependent mechanisms other than
the PRE determine the ESF lifetime. |
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