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This paper is primarily concerned with an event observed from 16:30 to24:30 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 gravitywave (GW) signature. Derived vertical and horizontal wavelengths, maximumamplitude, apparent and intrinsic period, and horizontal phase velocity wereabout ~ 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 particularinterest is a temporal development of the uppermost altitude that the GWreached. 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 (above100 km). We have evaluated three mechanisms (critical-level filtering,convective and dynamic instabilities) for dissipations using data obtained bythe sodium LIDAR and a meteor radar. It is found that critical-levelfiltering did not occur, and the convective and dynamic instabilitiesoccurred on some occasions. MF radar echo power showed significantenhancements between 18:30 and 21:00 UT, and an overturning feature of thesodium mixing ratio was observed between 18:30 and 21:20 UT above about95 km. From these results, we have concluded that the GW was dissipated by wave breaking and instabilities before 21:00 UT. We have alsoinvestigated the difference of the background atmosphere for the twointervals and would suggest that a probable cause of the change in the GWpropagation was due to the difference in the temperature gradient of thebackground atmosphere above 94 km

A case study of gravity wave dissipation in the polar MLT region using sodium LIDAR and radar data