Abstract
An intriguing and rare gravity wave event was recorded on the night of 25 April 2017 using a multi-wavelength all-sky airglow imager over northern Germany. The airglow imaging observations at multiple altitudes in the mesosphere and lower thermosphere region reveal that a prominent upward propagating wave structure appeared in O(1S) and O2 airglow images. However, the same wave structure was observed to be very faint in OH airglow images, despite OH being usually one of the brightest airglow emissions. In order to investigate this rare phenomenon, the altitude profile of the vertical wavenumber was derived based on collocated meteor radar wind-field and SABER temperature profiles close to the event location. The results indicate the presence of a thermal duct layer in the altitude range of 85–91 km in the south-west region of Kühlungsborn, Germany. Utilizing these instrumental datasets, we present an evidence to show how a leaky duct layer partially inhibited the wave progression in the OH airglow emission layer. The coincidental appearance of this duct layer caused the wave amplitudes to diminish, resulting to exhibit as the faint wave front in the OH airglow images during the course of the night over northern Germany.
Highlights
Multi-wavelength nighttime all-sky airglow imaging has become a widely used technique to retrieve valuable information of atmospheric gravity waves (GWs) as well as the dynamics of the mesosphere and lower thermosphere (MLT) region
Figures 2(g-l) depict the 170 corresponding 2D FFT filtered images overlaid on the MMARIA horizontal 1 hour averaged wind field in two dimensions at the centroid height of O(1S) airglow emission in the MLT region
The bottom subplots represent their corresponding 2D FFT filtered images overlaid on the MMARIA 2D horizontally resolved wind field 175 at the centroid height of the respective airglow emissions
Summary
Multi-wavelength nighttime all-sky airglow imaging has become a widely used technique to retrieve valuable information of atmospheric gravity waves (GWs) as well as the dynamics of the mesosphere and lower thermosphere (MLT) region. GWs play a key role in the upper atmospheric dynamics because of their inherent properties of transferring momentum and energy from lower atmospheric regions to the middle and upper atmosphere (Fritts and Alexander, 2003). The earlier imaging studies using airglow emissions originating in the MLT region revealed different types of dynamical events like quasimonochromatic GWs, ripples, mesospheric fronts (Taylor et al 1995; Walterscheid et al, 1999; Hecht et al, 2001; Smith et al, 2003; Makhlouf et al, 1995; Bageston et al, 2011; Lakshmi Narayanan et al., 2012; Sarkhel et al, 2012; 2015a; 2015b; 2019; Hozumi et al, 2019; Mondal et al, 2021). Large-scale waves can reach to the MLT region depending on their phase velocity compared to the background mean flow whereas small-scale waves are more susceptible to thermal and Doppler ducting (Walterscheid et al, 1999). GWs propagation through a region of thermal/Doppler ducting can explain some of the properties of mesospheric fronts like the long-distance horizontal propagation
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