 |
| Titel |
High-speed solar wind streams and polar mesosphere winter echoes at Troll, Antarctica |
| VerfasserIn |
S. Kirkwood  , A. Osepian, E. Belova, Y.-S. Lee |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 33, no. 6 ; Nr. 33, no. 6 (2015-06-01), S.609-622 |
| Datensatznummer |
250121201
|
| Publikation (Nr.) |
 copernicus.org/angeo-33-609-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| A small, 54 MHz wind-profiler radar, MARA, was operated at Troll, Antarctica
(72° S, 2.5° E), continuously from November 2011 to
January 2014, covering two complete Antarctic winters. Despite very low
power, MARA observed echoes from heights of 55–80 km (polar mesosphere winter
echoes, PMWE) on 60% of all winter days (from March to October). This
contrasts with previous reports from radars at high northern latitudes, where
PWME have been reported only by very high power radars or during rare periods
of unusually high electron density at PMWE heights, such as during solar
proton events. Analysis shows that PWME at Troll were not related to solar
proton events but were often closely related to the arrival of high-speed
solar wind streams (HSS) at the Earth, with PWME appearing at heights as low
as 56 km and persisting for up to 15 days following HSS arrival. This
demonstrates that HSS effects penetrate directly to below 60 km height in
the polar atmosphere. Using local observations of cosmic-noise absorption
(CNA), a theoretical ionization/ion-chemistry model and a statistical model
of precipitating energetic electrons associated with HSS, the electron
density conditions during the HSS events are estimated. We find that PMWE
detectability cannot be explained by these variations in electron density and
molecular-ion chemistry alone. PWME become detectable at different thresholds
depending on solar illumination and height. In darkness, PWME are detected
only when the modelled electron density is above a threshold of about
1000 cm−3, and only above 75 km height, where negative ions are few.
In daylight, the electron density threshold falls by at least 2 orders of
magnitude and PWME are found primarily below 75 km height, even in
conditions when a large proportion of negative ions is expected. There is
also a strong dawn–dusk asymmetry with PWME detected very rarely during
morning twilight but often during evening twilight. This behaviour cannot be
explained if PMWE are caused by small-scale structure in the
neutral/molecular-ion gas alone but may be explained by the presence of
charged meteoric dust. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|