Abstract
Abstract. Gravity waves are an important feature of mesosphere - lower thermosphere (MLT) dynamics, observed using many techniques and providing an important mechanism for energy transfer between atmospheric regions. It is known that some gravity waves may propagate through the mesopause and reach greater altitudes before eventually "breaking" and depositing energy. The generation, propagation, and breaking of upper thermospheric gravity waves have not been studied directly often. However, their ionospheric counterparts, travelling ionospheric disturbances (TIDs), have been extensively studied in, for example, radar data. At high latitudes, it is believed localised auroral activity may generate gravity waves in-situ. Increases in sensor efficiency of Fabry-Perot Interferometers (FPIs) located in northern Scandinavia have provided higher time resolution measurements of the auroral oval and polar cap atomic oxygen red line emission at 630.0 nm. A Lomb-Scargle analysis of this data has shown evidence of gravity wave activity with periods ranging from a few tens of minutes to several hours. Oscillations are seen in the intensity of the line as well as the temperatures and line of sight winds. Instruments are located in Sodankylä, Finland; Kiruna, Sweden; Skibotn, Norway, and Svalbard in the Arctic Ocean. A case study is presented here, where a wave of 1.8 h period has a phase speed of 250 ms-1 with a propagation angle of 302°, and a horizontal wavelength of 1600 km. All the FPIs are co-located with EISCAT radars, as well as being supplemented by a range of other instrumentation. This allows the waves found in the FPI data to be put in context with the ionosphere and atmosphere system. Consequently, the source region of the gravity waves can be determined.
Highlights
Atmospheric gravity waves are an important mechanism for the transfer of energy and momentum throughout the atmosphere
The aim of this paper is to show gravity waves have been found in the upper thermosphere in the northern auroral oval and polar cap regions, in neutral atom emission intensities as well as temperatures and winds
It is a potentially good night to find gravity waves because Travelling Ionospheric Disturbances (TIDs) appear to be present as clear wavefronts can be seen in the electron density (Fig. 2a)
Summary
Atmospheric gravity waves are an important mechanism for the transfer of energy and momentum throughout the atmosphere. Gravity waves have mostly been studied in the stratosphere, mesosphere, and lower thermosphere regions as these have the largest powers and so have a significant role. AGWs are important as they can transport energy and momentum large distances, for example, redistributing energy to equatorial latitudes. Gravity waves have been observed in the upper thermosphere over the southern polar cap, for example, by de Deuge et al (1994) and Innis et al (2001) with photometer observations of the 630.0 nm oxygen emissions and by Innis and Conde (2002) in satellite data. Innis and Conde (2001) observed gravity waves in vertical thermospheric winds from the Dynamics Explorer 2 (DE2) satellite Gravity waves have been observed in the upper thermosphere over the southern polar cap, for example, by de Deuge et al (1994) and Innis et al (2001) with photometer observations of the 630.0 nm oxygen emissions and by Innis and Conde (2002) in satellite data. Innis and Conde (2001) observed gravity waves in vertical thermospheric winds from the Dynamics Explorer 2 (DE2) satellite
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