Distribution of medium-scale acoustic gravity waves in polar regions according to satellite measurement data

A dominant acoustic-gravity mode in the polar thermosphere

“…The directions of AGW propagation follow a systematic behaviour suggesting that their propagation is controlled by the wind (Fedorenko and Kryuchkov, 2011b). The most evident feature is the predominant propagation of AGW from the nightside to the dayside, i.e.…”

“…It is easy to see that the wave propagates in reverse flight direction (leftwards in the plot). Almost all observed polar AGWs were propagating towards the dayside (Johnson et al, 1995;Fedorenko and Kryuchkov, 2011a). Note that the systematic phase shift between the density variation of different gases in Fig.…”

“…In the day sector the region of increased wave activity is bounded by the auroral oval, but in the night sector it can span down to lower geomagnetic latitudes. The dominant horizontal wavelength in the polar thermosphere is 500-600 km (Fedorenko and Kryuchkov, 2011a;Johnson et al, 1995). In the following subsections we briefly summarize the main features of polar AGWs as deduced primarily from DE2 measurements.…”

“…2 we plotted relative variations of densities of individual gases above the pole. The increase of the amplitude with the growth of the molecular mass (on the right) and the quasi-antiphase oscillations of He and heavy gases (on the left) are the characteristic signatures of AGW (Dudis and Reber, 1976;Fedorenko and Kryuchkov, 2011a).…”

“…It follows from the analysis of Dynamics Explorer 2 (DE2) data that at heights from 250 to 400 km above the polar caps the AGWs with wavelengths of several hundreds of kilometres are systematically observed at different geomagnetic activity levels (Fedorenko and Kryuchkov, 2011a). DE2's orbit with the perigee 250 km, the apogee 1000 km, and the inclination 89.9…”