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The behaviour of the zonal prevailing wind in the autumn mesosphere/lower thermosphere (MLT) and its correlations with dynamical processes in the lower atmosphere is considered in terms of the autumn transition date (ATD) variability. The ATD is defined as the day when the rate of zonal wind decrease in the MLT region reaches its maximum in September–October. The method is applied to MLT radar wind data obtained at Collm (52°N, 15°E) and Obninsk (55°N, 37°E) during 1979–2007 and 1979–2011, respectively. The interannual variability of the ATDs depends on the direction of the stratospheric equatorial zonal winds at 30 hPa, i.e. the phase of the equatorial quasi-biennial oscillation (QBO). There is also a statistically significant correlation between the ATDs and the Northern Annular Mode (NAM) index taken at upper tropospheric/lower stratospheric heights during the westerly phase of the QBO. Numerical simulations with a mechanistic global circulation model demonstrate that high NAM indices correspond to later ATD and that the ATD, defined from the zonal wind characteristics, depends on the gravity wave flux.

The interannual variability of a 5–7 day wave was investigated on the basis of Obninsk meteor wind data (1979–2010), Microwave Limb Sounder geopotential heights (2004–2011) and ERA project data (1958–2011) for August–September. Several points of evidence were found indicating that the wave variabilities in the mid-latitude mesosphere/lower thermosphere (MLT) and in the lower stratosphere are significantly connected in the Northern Hemisphere. Statistically significant correlations between the year-to-year variability of the wave period (+0.86) and the date of the amplitude maxima (+0.71) estimated from the Obninsk meridional wind data and the ERA project geopotential heights (at 1 hPa) are obtained if the years 1980, 1989, 2006 and 2008 are excluded as years with a significant difference between the wave periods at the two levels. There is also a possible influence of the wave activity from the Southern Hemisphere. According to the MLS geopotential heights, the wave could not have readily propagated into the mid-latitude MLT from the stratosphere in 2006 and 2008, though we found that it can propagate from the Southern Hemisphere through the equator into the Northern Hemisphere. For other MLS years, the statistically significant coherent behaviour of geopotential height oscillations is observed in the mid-latitude MLT and upper stratosphere during August–September. In turn, the interannual variability of the wave amplitudes in the mid-latitude upper stratosphere are significantly anti-correlated (−0.8) with the variability of the Northern Annular Mode index at upper troposphere heights under eastward quasi-biennial equatorial winds taken at 50 hPa. There is no significant correlation under the opposite phase possibly because of some leakage of the wave activity from the Southern Hemisphere into the Northern Hemisphere through the equator.

Long-term variability of the mesosphere/lower thermosphere (lower E region ionosphere) since 1970 has been analyzed using wind data series obtained at Collm (52° N, 15° E) using the LF drift method and at Obninsk (55° N, 37° E) applying VHF meteor radar. Applying piecewise linear trend analysis with a priori unknown number and positions of breakpoints shows that trend models with breakpoints are generally to be preferred against straight lines. There is a strong indication for a change of trends in wind parameters around 1975–1980. Similar changes are also found in the lower atmosphere, e.g., in tropospheric temperatures. This indicates a coupling between atmospheric layers at time scales of decades.

Recent analysis of the long-term behavior of different geophysical data has demonstrated that trend parameters can change during a period of observation. Sophisticated general methods for an objective analysis of structural changes in linear trends have been developed during the last 10 years. Such methods are applied for an analysis of changes in trend parameters of the mesosphere/lower thermosphere wind observed over Obninsk (55°N, 37°E) from 1964 to 2007 and Collm (52°N, 15°E) from 1979 to 2008, respectively. We found that trend models with breakpoints are generally preferred against straight lines. At Obninsk, there are break-years in trends of the winter prevailing winds close to 1977, when a climatic regime shift was observed. The break-years in trends of the semidiurnal tides for both stations are close to years of possible changes in stratospheric ozone. Correlations of the Obninsk and Collm winds with atmospheric indices are also considered.

We present time series of January–May mean mesosphere/lower thermosphere (MLT) mean winds and planetary wave (PW) proxies over Europe together with stratospheric stationary planetary waves (SPW) at 50°N and time series of European ozone laminae occurrence. The MLT winds are connected with stratospheric PW and laminae at time scales of several years to decades. There is a tendency for increased wave activity after 1990, together with more ozone laminae and stronger MLT zonal winds. However, possible coupling processes are not straightforward. While mean MLT winds before the 1990s show similar interannual variations than stratospheric PW at 100 hPa, later a tendency towards a connection of the MLT with the middle stratosphere SPW is registered. There is also a tendency for a change in the correlation between lower and middle stratosphere SPW, indicating that coupling processes involving the European middle atmosphere from the lower stratosphere to the mesopause region have changed.

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 (0–100 km) 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.

Tendencies of mesosphere/lower thermosphere winds are investigated using updated multi-year ground-based data obtained at three mid-latitude stations located at Collm (Germany), Obninsk (Russia) and Saskatoon (Canada). For the first time for the mesosphere/lower thermosphere winds we consider in this study a family of trends, which includes both broken and straight-lines, to check a possible change of the wind tendencies during 1964–2004. General peculiarities of year-to-year wind variations are considered for annual mean, winter and summer prevailing winds and semidiurnal tides. Our results suppose a change in rates/directions of wind tendencies during the time interval 1964–2004. In particular, the annual mean zonal (eastward) wind decreases until the 1980s, but after that does not have a significant trend; similarly, the annual mean meridional (northward) wind increases until the 1990s and then does not have a significant trend. The behaviour of the summer prevailing wind both for the meridional and zonal components differ from that of annual winds, so that they increase after the trend's break. Rather large rates of decrease of tidal amplitudes (1.1–1.4 m/s/year) in the earlier years of measurements become smaller (about 6 times) in the beginning of the 1970s.

Two very long data sets of mesopause region winds measured over Obninsk (55°N, 37°E) and Collm (52°N, 15°E) in the time interval 1973–2000 are compared. Measurements are carried out using a meteor radar at Obninsk and the LF D1 method at Collm. The meteor wind measurements over Obninsk were carried out without height resolution. The long-term means of both prevailing and tidal winds show good correspondence if a reference height of 90–92 km for Obninsk is assumed. The interannual and interdecadal variability of the prevailing winds is different over Collm and Obninsk. This is probably partly due to regional variations of the mesospheric/lower thermospheric wind field. The semidiurnal tidal amplitudes have decreased during the last 30 years over both Central and Eastern Europe, which is accompanied by a shift in the semidiurnal tidal phase.

The Arctic MLT wind regime parameters measured at the ground-based network of MF and meteor radar stations (Andenes 69° N, Tromsø 70° N, Esrange 68° N, Dixon 73.5° N, Poker Flat 65° N and Resolute Bay 75° N) are discussed and compared with those observed in the mid-latitudes. The network of the ground-based MF and meteor radars for measuring winds in the Arctic upper mesosphere and lower thermosphere provides an excellent opportunity for study of the main global dynamical structures in this height region and their dependence from longitude. Preliminary estimates of the differences between the measured winds and tides from the different radar types, situated 125-273km apart (Tromsø, Andenes and Esrange), are provided. Despite some differences arising from using different types of radars it is possible to study the dynamical wind structures. It is revealed that most of the observed dynamical structures are persistent from year to year, thus permitting the analysis of the Arctic MLT dynamics in a climatological sense. The seasonal behaviour of the zonally averaged wind parameters is, to some extent, similar to that observed at the moderate latitudes. However, the strength of the winds (except the prevailing meridional wind and the diurnal tide amplitudes) in the Arctic MLT region is, in general, less than that detected at the moderate latitudes, decreasing toward the pole. There are also some features in the vertical structure and seasonal variations of the Arctic MLT winds which are different from the expectations of the well-known empirical wind models CIRA-86 and HWM-93. The tidal phases show a very definite longitudinal dependence that permits the determination of the corresponding zonal wave numbers. It is shown that the migrating tides play an important role in the dynamics of the Arctic MLT region. However, there are clear indications with the presence in some months of non-migrating tidal modes of significant appreciable amplitude.

Long-term wind measurements carried out at 6 northern midlatitude sites (Saskatoon, Sheffield, Juliusruh, Collm, Obninsk, Kazan) are investigated to establish a climatology of the semidiurnal tide in the mesopause region for the narrow latitudinal range between 52°N and 56°N. Comparison of zonal and meridional components shows that in general the horizontal components are circularly polarized. Intercomparison of amplitudes and phases generally shows good agreement between the results from the different measuring systems. The results are compared with an empirical model of the semidiurnal tide. The longitudinal variation of the semidiurnal tide is small in summer, but the tidal amplitudes in winter are larger at Saskatoon and Kazan, compared with the results from the other sites. The possible influence of wave–tidal interaction in the stratosphere on the interannual variability of this difference is discussed.

The seasonal variations of the zonal winds measured by meteor/MF radars and by the wind-imaging interferometer (WINDII) on board of the UARS satellite, are analyzed and compared with the ground-based Global Empirical Wind Model (GEWM) and satellite-based WINDII prevailing wind model, which are independently derived from the observational data sets. A general consistency in the main global scale wind structures is observed. The seasonal variations of zonal wind in the both models are described by almost the same annual and semi-annual components. But systematic bias is found for the annual mean zonal winds of the two models, with the GEWM winds generally smaller than those of WINDII by factor 2–2.5. This bias is practically independent of altitude and can be described by a term of A cos 4x, where A is about 20 m/s and x is colatitude. Possible origin of this offset is discussed.

Wind measurements carried out at 6 European sites are investigated to set up a climatology of the semidiurnal tide in the mesopause region over Europe for the latitudinal range between 50°N and 56°N. Intercomparison of amplitudes and phases generally shows good agreement of the results from the different measuring systems. The longitudinal variation of the semidiurnal tide is small. The results are compared with an empirical model of the semidiurnal tide.

Observational amplitudes and phases of semidiurnal tidal oscillations from over 30 meteor and MF radar facilities extending from 65° N to 68° S are utilized to construct a 2-D empirical model of the migrating semidiurnal tide (ST). The model extends from 80 to 100 km and has been constructed for all months of the year. A characteristic feature of the model is a distinct ST amplitude saturation in the lower thermosphere. Comparisons between the empirical model and available theoretical/numerical models, and with particular ground- and space-based data sets are presented.

The relative role in maintaining momentum balance in the lower thermosphere of different wave processes is considered. Based on the 2-D global empirical meridional wind model and on the empirical migrating semidiurnal tide model the momentum fluxes for different seasons are calculated. The main features of global structure of mean meridional winds in the lower thermosphere induced by semidiurnal tide (ST) propagation and dissipation are revealed.

Comparisons are made between climatological dynamic fields obtained from ground-based (GB) and space-based (SB) instruments with a view towards identifying SB/GB intercalibration issues for TIMED and other future aeronomy satellite missions. SB measurements are made from the High Resolution Doppler Imager (HRDI) instrument on the Upper Atmosphere Research Satellite (UARS). The GB data originate from meteor radars at Obninsk, (55° N, 37° E), Shigaraki (35° N, 136° E) and Jakarta (6° S, 107° E) and MF spaced-antenna radars at Hawaii (22° N, 160° W), Christmas I. (2° N, 158° W) and Adelaide (35° S, 138° E). We focus on monthly-mean prevailing, diurnal and semidiurnal wind components at 96km, averaged over the 1991-1999 period. We perform space-based (SB) analyses for 90° longitude sectors including the GB sites, as well as for the zonal mean. Taking the monthly prevailing zonal winds from these stations as a whole, on average, SB zonal winds exceed GB determinations by ~63%, whereas meridional winds are in much better agreement. The origin of this discrepancy remains unknown, and should receive high priority in initial GB/SB comparisons during the TIMED mission. We perform detailed comparisons between monthly climatologies from Jakarta and the geographically conjugate sites of Shigaraki and Adelaide, including some analyses of interannual variations. SB prevailing, diurnal and semidiurnal tides exceed those measured over Jakarta by factors, on the average, of the order of 2.0, 1.6, 1.3, respectively, for the eastward wind, although much variability exists. For the meridional component, SB/GB ratios for the diurnal and semidiurnal tide are about 1.6 and 1.7. Prevailing and tidal amplitudes at Adelaide are significantly lower than SB values, whereas similar net differences do not occur at the conjugate Northern Hemisphere location of Shigaraki. Adelaide diurnal phases lag SB phases by several hours, but excellent agreement between the two data sources exists for semidiurnal tidal phases throughout the year. These results are consistent with phase retardation effects in the MF radar technique that are thought to exist above about 90km. Prevailing and tidal amplitudes from Shigaraki track year-to-year variations in SB fields, whereas in the Southern Hemisphere poorer agreement exists. The above hemispheric differences are due in part to MF vs. meteor radar techniques, but zonal asymmetries and day-to-day variability, combined with inadequate sampling, may also be playing a role. Based on these results, some obvious recommendations emerge that are relevant to combined GB/SB studies as part of TIMED and other future aeronomy missions.