Abstract
Abstract. An all-sky airglow imager (ASAI) was installed at Xinglong, in northern China (40.2° N, 117.4° E) in November 2009 to study the morphology of atmospheric gravity waves (AGWs) in the mesosphere and lower thermosphere (MLT) region. Using one year of OH airglow imager data from December 2009 to November 2010, the characteristics of short-period AGWs are investigated and a yearlong AGW climatology in northern China is first ever reported. AGW occurrence frequency in summer and winter is higher than that in equinoctial months. Observed bands mainly have horizontal wavelengths from 10 to 35 km, observed periods from 4 to 14 min and observed horizontal phase speeds in the range of 30 to 60 m s−1. Most of the bands propagate in the meridional direction. The propagation directions of the bands show a strong southwestward preference in winter, while almost all bands propagate northeastward in summer. Although the wind filtering in the middle atmosphere may control AGW propagations in the zonal direction, the non-uniform distribution of wave sources in the lower atmosphere may contribute to the anisotropy in the meridional direction in different seasons. Additionally, as an indication of local instability, the characteristics of ripples are also analyzed. It also shows seasonal variations, occurring more often in summer and winter and mainly moving westward in summer and eastward in winter.
Highlights
The atmospheric gravity wave (AGW) is an important atmospheric phenomenon (Hines, 1960)
We study the characteristics of wave patterns, including both bands and ripples, observed by the all-sky airglow imager (ASAI) of near infrared (NIR) hydroxyl (OH)
To start the statistical study of the AGWs observed by the Xinglong imager, we checked the observing weather condition and the occurrence frequency of wave structures for each month from December 2009 to November 2010
Summary
The atmospheric gravity wave (AGW) is an important atmospheric phenomenon (Hines, 1960). Bands are large-scale, long-lived and often extended over the entire field of view These AGWs can propagate freely or be ducted by thermal and/or wind ducts in the MLT (Isler et al, 1997; Walterscheid et al, 1999; Hecht et al, 2001b; Snively and Pasko, 2005). The large-scale structures in airglow images, such as lowfrequency AGWs, tides, Milky Way and abrupt background change can distort the wave spectrum calculation. To remove this distortion, we take a step of detrending, which involves fitting a plane (constant) to the TD images and subtracting the plane from the TD images.
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