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Abstract: During recent years, special attention has been paid to understanding the background circulation of the middle atmosphere. Particularly in the mesosphere/lower thermosphere (MLT) region, this has involved including data from a range of new radar measurements. It has also involved the comparison of existing empirical middle atmosphere wind models, such as CIRA-86 and HWM-93 to the new data. This has led to the construction of empirical models of MLT winds such as the Global Empirical Wind Model (GEWM). Further investigations are aimed at the construction of new empirical and semi-empirical wind models of the entire middle atmosphere including these new experimental results. The results of a new wind climatology (0–100km) are presented here, based upon the GEWM, a reanalysis of stratospheric data, and a numerical model which is used to fill the gap between data from the stratospheric and MLT regions. [Copyright &y& Elsevier]

Abstract: An updated mechanistic circulation model is used to calculate monthly tables of winds and temperatures in the middle atmosphere, including mean values, tides, and stationary planetary waves. The model includes realistic background ozone and water vapour climatologies and a long-term mean stationary planetary wave forcing from Met Office analyses. The results are compared with existing empirical climatologies. The model climatology may be used as reference values for measurements, or to complete empirical climatologies especially for the height regions not well covered with measurements. [Copyright &y& Elsevier]

Abstract: Radar measurements of mesosphere/lower thermosphere winds are carried out since several decades, now allowing the detection of long-term trends and to distinguish from long-period oscillations connected with the solar cycle or atmospheric decadal variability. Here we analyse Collm (52°N, 13°E) LF mean winds near 95km. The analysis of prevailing winds, tidal amplitudes and phases show (1) a decrease of the summer meridional wind. This change is probably due to modifications of gravity wave filtering through the mesospheric summer jet, (2) a tendency for a decrease of semidiurnal tidal amplitudes, connected with a tidal phase shift. This decrease possibly originates from a combination of CO2 increase and ozone decrease, and (3) an increase of the westerly wind in the mesopause region, probably connected with tropospheric circulation variability and anthropogenic climate change. [Copyright &y& Elsevier]

Collm (52°N, 15°E) mid-latitude mesosphere/lower thermosphere (MLT) zonal winds are investigated with respect to a possible influence of the Southern Oscillation (SO). It is found that in winter the prevailing wind is positively correlated with the Southern Oscillation index (SOI), which qualitatively fits to the response of the low-latitude stratosphere on the SO. In summer, however, there is a negative correlation between MLT zonal winds and SOI. A possible mechanism, which includes slightly enhanced planetary wave propagation to the MLT in summers of low SOI is discussed. [Copyright &y& Elsevier]

Abstract: This work presents an analysis of spectra and estimations of zonal wavenumbers for mean wind and semidiurnal tide amplitude oscillations observed during July–September 1998 by 3 meteor radars and one MF radar. A number of mean wind and tidal amplitude oscillations are found that are possibly related to the evolution of the summer mesospheric zonal wind jet. The mean zonal wind undergoes several significant variations (“transitions”) during this time interval. These changes were accompanied by a frequency decreasing of the QTDW (quasi-2-day wave) in such a way that oscillations with a period of roughly about 36–44h at the beginning of the measurements were replaced by strong 48-h waves, which in its turn after the end of the QTDW burst are replaced by a set of 3–6 day oscillations. Before the strong 48-h wave appearance we observe mean zonal wind variations with a temporal scale of 4 days. The set of 3–6 days includes 3–4 day waves with and 5–6 day waves with . The last wave is absent in the upper stratosphere during the time of observations and suggests to appear in the mesosphere. The both waves could represent a signature of the simultaneous non-linear excitation of a triad of waves. The zonal wind “transitions” also reflected in the semidiurnal tide by modulations of the tidal amplitudes with periods of 3–4 days and about 5 days. Some features observed at the end of summer 1998 could be explained by interaction between a zonally averaged wind variation and the semidiurnal tide. In a spectral representation, this variation looks like an oscillation, but is not a planetary wave. The strongest long-period modulations of the semidiurnal tide were observed during strong geopotential perturbations in the stratosphere of the Southern hemisphere. [Copyright &y& Elsevier]

The GPS/MET satellite measurements during years 1995–1997 at altitudes 2–35 km are used to obtain global distributions of meso-scale variances of the refraction index (“dry temperature”) at different stratospheric altitudes. Individual dry temperature profiles are smoothed using second order polynomial approximations in 7 km thick layers centered at 2, 5, 10, 15, 20, 25, 30 and 35 km. Refraction index deviations from smoothed values and their variances are obtained for each profile and are averaged for each month of the year during the GPS/MET experiment. Global distributions of dry temperature variances have inhomogeneous structure. Locations and latitude distributions of the variance maxima and minima depend on altitudes and months of year. The reasons for the small- and meso-scale refraction index perturbations in the tropo–stratosphere could be meso-scale irregularities, turbulence and internal gravity waves. Magnitudes of the refraction index variances are larger in the regions of tropo–stratrospheric jet streams and of equatorial deep convection. [Copyright &y& Elsevier]

The mesosphere/lower thermosphere (MLT) wind data from the 46 ground-based (GB) MF and meteor radar (MR) stations, located at the different latitudes over the globe, and the space-based (SB) HRDI data were used for constructing of the empirical global climatic 2-D prevailing wind model at 80–100 km heights for all months of the year. The main data set is obtained during 1990–2001 period. It is shown that the three datasets (MF, MR, HRDI) are mainly well correlated. However, a certain systematic bias between the GB and SB data at 96 km exists, as well as that between the MF and MR data higher 88 km. Simple correction factors are proposed to minimize these biases. The 2-D distant-weighted least-square interpolation procedure for some arbitrary collection of points was used for drawing model contour plots. The model is available in the computer readable form and may be used for construction of the new CIRA model. [Copyright &y& Elsevier]