The upper mesosphere/lower thermosphere wind field nonzonality as possible sign of the external forcing from above and from below

Dynamical Climatology of the Upper Mesosphere, Lower Thermosphere and Ionosphere

“…But experiments have revealed this non-zonality. The similar pattern of the zonal prevailing wind response to strong geomagnetic storms for Badary (East Siberia) and Collm (Central Europe) is clearly visible e.g, from Figure 10 (Kazimirovsky et al, 1999). We can say that during strong (Ap >100) magnetic storm the zonal wind speed decreases at both sites, but after the storm some differences remain (e.g., the time of returning to the level preceding key day is different).…”

“…However, the systematic differences between similar seasonal variations are evident for semi-diurnal meridional tide amplitudes (V 2y ) that are systematically larger over Siberia than over Europe. The longitudinal variation of the semi-diurnal tidal amplitudes is possibly a consequence of the longitudinal variation of the mean flow (Kazimirovsky et al, , 1999 or a consequence of the nonlinear wave-mean flow and wave-wave interactions (see below, Section 3.5).…”

“…Details of both the regularities and regional distinctions for Collm and Badary are given in numerous publications (e.g., Schminder et al, 1980Schminder et al, , 1987Kazimirovsky et al, 1988Kazimirovsky et al, , 1999Kazimirovsky and Kokourov, 1991;Kazimirovsky and Vergasova, 2001b). The detailed long-term comparison of MLT winds at Collm and Saskatoon, Canada (52°N, 107°W) was realized for 1983-1998 by Jacobi et al (2001a, b).…”

Indications of long-term changes in the lower thermosphere prevailing zonal wind regime

“…It is known that in the winter months the wind reversals in the lower thermosphere can be associated with sudden stratospheric warmings and the spring circulation rearrangements there often coincide in time with so-called "final" stratospheric warmings [e.g., Kazimirovsky et al, 2003]. Principally, strong geomagnetic storms can be also associated with the lower thermosphere wind reversals [e.g., Kazimirovsky et al, 1999]. The variations in daily values of the prevailing zonal wind velocity (Vox) are shown in Figure 2 for two observatories and 10-11 years of observations.…”

“…The technique of these measurements (space diversity reception method in the LF range) was numerously described [e.g., Kazimirovsky and Vergasova, 2001]. The statistical analysis of data and comparison of the results made it possible to establish the mean climatic norms for the seasonal variations of the prevailing (mean, background) wind and to reveal the longitudinal (regional) variability of the lower thermosphere wind regime possibly associated to the external forcing from below [Kazimirovsky and Vergasova, 2001;Kazimirovsky et al, 1999Kazimirovsky et al, , 2003].…”