A case study of gravity wave dissipation in the polar MLT region using sodium LIDAR and radar data
This paper is primarily concerned with an event observed from 16:30 to 24:30 UT on 29 October 2010 during a very geomagnetically quiet interval (Kp ≤ 1). The sodium LIDAR observations conducted at Tromsø, Norway (69.6° N, 19.2° E) captured a clearly discernible gravity wave (G...
| Main Authors: | , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-10-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/32/1195/2014/angeo-32-1195-2014.pdf |
| Summary: | This paper is primarily concerned with an event observed from 16:30 to
24:30 UT on 29 October 2010 during a very geomagnetically quiet interval
(Kp ≤ 1). The sodium LIDAR observations conducted at Tromsø, Norway
(69.6° N, 19.2° E) captured a clearly discernible gravity
wave (GW) signature. Derived vertical and horizontal wavelengths, maximum
amplitude, apparent and intrinsic period, and horizontal phase velocity were
about ~ 11.9 km, ~ 1.38 × 10<sup>3</sup> km, ~ 15 K, 4 h,
~ 7.7 h, and ~ 96 m s<sup>−1</sup>, respectively, between a height of 80 and 95 km. Of particular
interest is a temporal development of the uppermost altitude that the GW
reached. The GW disappeared around 95 km height between 16:30 and 21:00 UT,
while after 21:00 UT the GW appeared to propagate to higher altitudes (above
100 km). We have evaluated three mechanisms (critical-level filtering,
convective and dynamic instabilities) for dissipations using data obtained by
the sodium LIDAR and a meteor radar. It is found that critical-level
filtering did not occur, and the convective and dynamic instabilities
occurred on some occasions. MF radar echo power showed significant
enhancements between 18:30 and 21:00 UT, and an overturning feature of the
sodium mixing ratio was observed between 18:30 and 21:20 UT above about
95 km. From these results, we have concluded that the GW was dissipated by wave breaking and instabilities before 21:00 UT. We have also
investigated the difference of the background atmosphere for the two
intervals and would suggest that a probable cause of the change in the GW
propagation was due to the difference in the temperature gradient of the
background atmosphere above 94 km. |
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| ISSN: | 0992-7689 1432-0576 |