Seasonal and intra-diurnal variability of small-scale gravity waves in OH airglow at two Alpine stations

Patrick Hannawald, Carsten Schmidt, René Sedlak, Sabine Wüst, Michael Bittner
2019 Atmospheric Measurement Techniques  
<p><strong>Abstract.</strong> Between December 2013 and August 2017 the instrument FAIM (Fast Airglow IMager) observed the OH airglow emission at two Alpine stations. A year of measurements was performed at Oberpfaffenhofen, Germany (48.09<span class="inline-formula"><sup>∘</sup></span><span class="thinspace"></span>N, 11.28<span class="inline-formula"><sup>∘</sup></span><span class="thinspace"></span>E) and 2 years at Sonnblick, Austria (47.05<span
more » ... n class="thinspace"></span>N, 12.96<span class="inline-formula"><sup>∘</sup></span><span class="thinspace"></span>E). Both stations are part of the network for the detection of mesospheric change (NDMC). The temporal resolution is two frames per second and the field-of-view is 55<span class="thinspace"></span>km<span class="thinspace"></span><span class="inline-formula">×</span><span class="thinspace"></span>60<span class="thinspace"></span>km and 75<span class="thinspace"></span>km<span class="thinspace"></span><span class="inline-formula">×</span><span class="thinspace"></span>90<span class="thinspace"></span>km at the OH layer altitude of 87<span class="thinspace"></span>km with a spatial resolution of 200 and 280<span class="thinspace"></span>m per pixel, respectively. This resulted in two dense data sets allowing precise derivation of horizontal gravity wave parameters. The analysis is based on a two-dimensional fast Fourier transform with fully automatic peak extraction. By combining the information of consecutive images, time-dependent parameters such as the horizontal phase speed are extracted. The instrument is mainly sensitive to high-frequency small- and medium-scale gravity waves. A clear seasonal dependency concerning the meridional propagation direction is found for these waves in summer in the direction to the summer pole. The zonal direction of propagation is eastwards in summer and westwards in winter. Investigations of the data set revealed an intra-diurnal variability, which may be related to tides. The observed horizontal phase speed and the number of wave events per observation hour are higher in summer than in winter.</p>
doi:10.5194/amt-12-457-2019 fatcat:bhrwizubt5a6zpvvxahipgbx4e