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| Titel |
Seasonal variability and descent of mid-latitude sporadic E layers at Arecibo |
| VerfasserIn |
N. Christakis, C. Haldoupis, Q. Zhou, C. Meek |
| 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 ; 27, no. 3 ; Nr. 27, no. 3 (2009-03-02), S.923-931 |
| Datensatznummer |
250016427
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| Publikation (Nr.) |
 copernicus.org/angeo-27-923-2009.pdf |
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| Zusammenfassung |
| Sporadic E layers (Es) follow regular daily patterns in variability and
altitude descent, which are determined primarily by the vertical tidal wind
shears in the lower thermosphere. In the present study a large set of
sporadic E layer incoherent scatter radar (ISR) measurements are analyzed.
These were made at Arecibo (Geog. Lat. ~18° N; Magnetic Dip ~50°)
over many years with ISR runs lasting from several hours to
several days, covering evenly all seasons. A new methodology is applied, in
which both weak and strong layers are clearly traced by using the vertical
electron density gradient as a function of altitude and time. Taking a time
base equal to the 24-h local day, statistics were obtained on the
seasonal behavior of the diurnal and semidiurnal tidal variability and
altitude descent patterns of sporadic E at Arecibo. The diurnal tide, most
likely the S(1,1) tide with a vertical wavelength around 25 km, controls
fully the formation and descent of the metallic Es layers at low
altitudes below 110 km. At higher altitudes, there are two prevailing layers
formed presumably by vertical wind shears associated mainly with semidiurnal
tides. These include: 1) a daytime layer starting at ~130 km around
midday and descending down to 105 km by local midnight, and 2) a less
frequent and weaker nighttime layer which starts prior to midnight at ~130 km,
descending downwards at somewhat faster rate to reach 110 km by
sunrise. The diurnal and semidiurnal-like pattern prevails, with some
differences, in all seasons. The differences in occurrence, strength and
descending speeds between the daytime and nighttime upper layers are not
well understood from the present data alone and require further study. |
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