Abstract
Abstract. Recent advances in the performance of CCD detectors have enabled a high time resolution study of the high latitude upper thermosphere with Fabry-Perot Interferometers (FPIs) to be performed. 10-s integration times were used during a campaign in April 2004 on an FPI located in northern Sweden in the auroral oval. The FPI is used to study the thermosphere by measuring the oxygen red line emission at 630.0 nm, which emits at an altitude of approximately 240 km. Previous time resolutions have been 4 min at best, due to the cycle of look directions normally observed. By using 10 s rather than 40 s integration times, and by limiting the number of full cycles in a night, high resolution measurements down to 15 s were achievable. This has allowed the maximum variability of the thermospheric winds and temperatures, and 630.0 nm emission intensities, at approximately 240 km, to be determined as a few minutes. This is a significantly greater variability than the often assumed value of 1 h or more. A Lomb-Scargle analysis of this data has shown evidence of gravity wave activity with waves with short periods. 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. At high latitudes gravity waves may be generated in-situ by localised auroral activity. Short period waves were detected in all four clear nights when this experiment was performed, in 630.0 nm intensities and thermospheric winds and temperatures. Waves with many periodicities were observed, from periods of several hours, down to 14 min. These waves were seen in all parameters over several nights, implying that this variability is a typical property of the thermosphere.
Highlights
Studying the small-scale structure of the thermosphere is important both to better understand the processes, such as the energetics and dynamics of the atmosphere, and to improve models of the atmosphere so that they can better predict physical quantities under different conditions
The all sky camera (ASC) keogram from Muonio, which is between the latitude of the KEOPS site and the tristatic position, is shown in Fig. 1, for 3 April 2004
ASC keograms are created by taking a vertical slice through the centre of each of the images from an ASC over the period of a night, and placed consecutively to show an overview of the night
Summary
Studying the small-scale structure of the thermosphere is important both to better understand the processes, such as the energetics and dynamics of the atmosphere, and to improve models of the atmosphere so that they can better predict physical quantities under different conditions. It is important to measure the thermosphere on small scales so that it can be understood over the same ranges as the ionosphere, and the structure within an instrument’s field of view can be observed. Since the ionosphere is known to exhibit small-scale structures such as auroral arcs, which are a few tens of kilometres in width, it is likely that we will observe meso-scale effects in the thermosphere, if the instrumentation present is sufficient to measure these effects. It is important to quantify and parameterise the small-scale variability to enable such models to improve their prediction of atmospheric values, especially under geomagnetically active conditions. Higher resolution data from this experiment will allow shorter period waves to be detected than have previously been seen in thermospheric data
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