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| Titel |
Coincident extremely large sporadic sodium and sporadic E layers observed in the lower thermosphere over Colorado and Utah |
| VerfasserIn |
B. P. Williams, F. T. Berkey, J. Sherman, C. Y. She |
| 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 ; 25, no. 1 ; Nr. 25, no. 1 (2007-02-01), S.3-8 |
| Datensatznummer |
250015756
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| Publikation (Nr.) |
 copernicus.org/angeo-25-3-2007.pdf |
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| Zusammenfassung |
| On the night of 2 June 2002, the sodium lidar in Fort Collins, CO (40.6 N,
105 W) measured an extremely strong sporadic sodium layer lasting from 03:30 to
05:00 UT with several weaker layers later in the night at 06:00 and 09:00 UT. There is a
double layer structure with peaks at 101 and 104 km. The peak sodium density
was 21 000 atoms/cm3 with a column abundance of up to twice that of the
normal sodium layer. The peak density was 500 times greater than the typical
density at that altitude. The sporadic layer abundance and strength factor
were higher than any reported in the literature. The two lidar beams,
separated by 70 km at this altitude, both measured 0.6 h periodicities in
the abundance, but out of phase with each other by 0.3 h. There is also
evidence for strong wave activity in the lidar temperatures and winds. The
NOAA ionosonde in Boulder, CO (40.0 N, 105 W) measured a critical frequency
(foEs) of 14.3 MHz at 03:00 UT on this night, the highest value
anytime during 2002. The high values of total ion density inferred means
that Na+ fraction must have been only a few percent to explain the
neutral Na layer abundances. The Bear Lake, Utah (41.9 N, 111.4 W) dynasonde
also measured intense Es between 02:00 and 05:00 UT and again from 06:00 to 08:00 UT
about 700 km west of the lidar, with most of the ionograms during these
intervals measuring Es up to 12 MHz, the limit of the ionosonde sweep.
Other ionosondes around North America on the NGDC database measured normal
foEs values that night, so it was a localized event within North
America. The peak of Es activity observed in Europe during the summer
of 2002 occurred on 4 June. The observations are consistent with the current
theories where a combination of wind shears and long period waves form and
push downward a concentrated layer of ions, which then chemically react and
form a narrow layer of sodium atoms. |
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