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

Patrick Hannawald,Sabine Wüst,René Sedlak,Michael Bittner,Carsten Schmidt

doi:10.5194/amt-12-457-2019

Patrick Hannawald, Sabine Wüst + Show 3 more

Open Access

https://doi.org/10.5194/amt-12-457-2019

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Abstract

Abstract. 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∘ N, 11.28∘ E) and 2 years at Sonnblick, Austria (47.05∘ N, 12.96∘ 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 km × 60 km and 75 km × 90 km at the OH layer altitude of 87 km with a spatial resolution of 200 and 280 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.

Highlights

Hydroxyl (OH) airglow, originally investigated by Meinel (1950), can be used as a tracer for atmospheric dynamics in the middle atmosphere, especially for the investigation of gravity waves (Peterson, 1979; Taylor et al, 1993; Gardner and Taylor, 1998 and many more)
We have shown two airglow observation data sets with high spatio-temporal resolution
The instrument FAIM was located in the Alpine region first at Oberpfaffenhofen, Germany (OPN, 48.09◦ N, 11.28◦ E) and at Sonnblick Observatory, Austria (SBO, 47.05◦ N, 12.96◦ E)

Summary

Introduction

Hydroxyl (OH) airglow, originally investigated by Meinel (1950), can be used as a tracer for atmospheric dynamics in the middle atmosphere, especially for the investigation of gravity waves (Peterson, 1979; Taylor et al, 1993; Gardner and Taylor, 1998 and many more). The OH airglow layer is located at about 87 km altitude and has a half-width (full width at half maximum) of roughly 8 km (Baker and Stair Jr., 1988). For example from von Savigny (2015) or Wüst et al (2017), show that the altitude change can be up to a few kilometres, the shape of the distribution with height may vary. Many OH bands contribute to the overall intensity in the visible and short-wave infrared range The intensity in the short-wave infrared is much higher than in the visible range. Exposure times of instruments observing the OH airglow can be much lower when addressing the short-wave infrared emissions (mainly OH(3-1) and OH(4-2)). The temporal resolution of the FAIM data is comparatively high, up to two frames per second (Hannawald et al, 2016; Sedlak et al, 2016)

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