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Meteor radar observations of mesosphere/lower thermosphere (MLT) daily temperatures have been performed at Collm, Germany since August 2004. The data have been analyzed with respect to long-period oscillations at time scales of 2--30 days. The results reveal that oscillations with periods of up to 6 days are more frequently observed during summer, while those with longer periods have larger amplitudes during winter. The oscillations may be considered as the signature of planetary waves. The results are compared with analyses from radar wind measurements. Moreover, the temperature oscillations show considerable year-to-year variability. In particular, amplitudes of the quasi 5-day oscillation have increased during the last decade, and the quasi 10-day oscillations are larger if the equatorial stratospheric winds are eastward. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Primary photoionisation of major ionospheric constituents is calculated from satellite-borne solar EUV measurements. Number densities of the background atmosphere are taken from the NRLMSISE-00 climatology. From the calculated ionisation rates, a proxy termed EUV-TEC, which is based on the global total ionisation is calculated, and describes the ionospheric response to solar EUV and its variability. The proxy is compared against the global mean ionospheric total electron content (TEC) derived from GPS data. Results show that the EUV-TEC proxy provides a better overall representation of global TEC than conventional solar indices like F10.7 do. The EUV-TEC proxy may be used for scientific research, and to describe the ionospheric effects on radio communication and navigation systems. [Copyright &y& Elsevier]

The recent solar minimum has been characterized by an anomalous strong decrease of thermospheric density since 2005. Here we analyze anomalies of mesosphere/lower thermosphere parameters possibly connected with this effect. In particular, nighttime mean LF reflection heights measured at Collm, Germany, show a very strong decrease after 2005, indicating a density decrease. This decrease is also visible in mean meteor heights measured with VHF meteor radar at Collm. This density decrease is accompanied by an increase of gravity wave (GW) amplitudes in the upper mesosphere and a decrease in the lower thermosphere. On the decadal scale, GWs are negatively correlated with the background zonal wind, but this correlation is modulated in the course of the solar cycle, indicating the combined effect of GW filtering and density decrease. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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 100hPa, 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. [Copyright &y& Elsevier]

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]

The response of the mesosphere/lower-thermosphere (MLT) region to a major stratospheric warming in Europe during winter 2000/2001 has been investigated using mesopause-region winds measured by meteor radar or the LF-D1 method over three stations (Castle Eaton, 52°N; Collm, 52°N; and Esrange 68°N). The vertical wind structure measured over the three sites, and its time evolution, are found to be quite similar despite the different techniques used in the measurements. The effects of stratospheric warming are very clear, and are similar over both the mid-latitude and high-latitude sites. The warming resulted in a reversal of both the zonal and meridional wind. In the zonal component, this reversal was apparently associated with a planetary-wave oscillation with a period of ∼10 days. The effect was most conspicuous in the vertical prevailing wind gradients. The mesopause-region effects thus seem to be the results of a superposition of an intensifying planetary wave and a slow overall decrease in the strength of the zonal prevailing winds. [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]

• Horizontal winds were measured by five meteor radars distributed from 13°E to 178°E in the middle and high-latitudes. • We studied planetary wave propagation during October 2017 – February 2018. • Planetary scale oscillations in the meridional wind are organized in groups. • Each group successively propagates from one site to another one. • Each group is observed at one site and almost disappears at the previous one. We present results of wind measurements near the mesopause carried out with meteor radars (MRs) at Collm (51°N, 13°E), Obninsk (55°N, 37°E), Kazan (56°N, 49°E), Angarsk (52°N, 104°E) and Anadyr (65°N, 178°E) from October 1, 2017 till March 31, 2018. The Collm and Kazan MRs are SKiYMET radars with vertical transmission and radio echo height finding, while the other radars operate with horizontal transmission and without height finding. We paid particular attention to the meridional wind variability with periods of 4–6 days and 9–11 days. The waves with these periods are seen as spots of the wave activity in the wavelet spectra and include oscillations with different periods and different discrete zonal wavenumbers. These wave packets successively propagate as a group of waves from one site to another one in such a way that they are observed at one site and almost disappear at the previous one. The 4–6 wave group includes planetary-scale oscillations (individual spectral components) which have eastward phase velocities and mostly zonal wavenumbers 2 and 3, and the vertical wavelength exceeds 70 km at middle latitudes. The source of the oscillations is the polar jet instability. The wave group itself propagates westward, and the amplitudes of wind oscillations are approximately 5–6 m/s as obtained from the wind data averaged over the meteor zone. The 9–11 day wave set propagates westward as a group and mainly consists of spectral components which have westward phase velocity and zonal wavenumber 1. Amplitudes of these wind perturbations strongly vary from station to station and can reach, approximately, 8 m/s. The vertical wavenumber is 0.014 km−1 as taken from the Kazan and 0.05 km−1 according to the Collm data. We obtained a global view on the waves by using the AURA MLS geopotential data. We found a good correspondence between wave features obtained from the MR wind measurements and the MLS data. To our knowledge, such a wave propagation of planetary wave in the mesosphere/lower thermosphere (MLT) region has so far not obtained much attention. [ABSTRACT FROM AUTHOR]

At the 10th Thermospheric Ionospheric GEospheric Research (TIGER/COSPAR) symposium held in Moscow in 2014 the achievements from the start of TIGER in 1998 were summarized. During that period, great progress was made in measuring, understanding, and modeling the highly variable UV-Soft X-ray (XUV) solar spectral irradiance (SSI), and its effects on the upper atmosphere. However, after more than 50 years of work the radiometric accuracy of SSI observation is still an issue and requires further improvement. Based on the extreme ultraviolet (EUV) data from the SOLAR/SolACES, and SDO/EVE instruments, we present a combined data set for the spectral range from 16.5 to 105.5 nm covering a period of 3.5 years from 2011 through mid of 2014. This data set is used in ionospheric modeling of the global Total Electron Content (TEC), and in validating EUV SSI modeling. For further investigations the period of 3.5 years is being extended to about 12 years by including data from SOHO/SEM and TIMED/SEE instruments. Similarly, UV data are used in modeling activities. After summarizing the results, concepts are proposed for future real-time SSI measurements with in-flight calibration as experienced with the ISS SOLAR payload, for the development of a space weather camera for observing and investigating space weather phenomena in real-time, and for providing data sets for SSI and climate modeling. Other planned topics are the investigation of the relationship between solar EUV/UV and visible/near-infrared emissions, the impact of X-rays on the upper atmosphere, the development of solar EUV/UV indices for different applications, and establishing a shared TIGER data system for EUV/UV SSI data distribution and real-time streaming, also taking into account the achievements of the FP7 SOLID (First European SOLar Irradiance Data Exploitation) project. For further progress it is imperative that coordinating activities in this special field of solar–terrestrial relations and solar physics is emphasized. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of the paper is to answer the question if planetary waves (PW) are capable of propagating into the thermosphere. First the simplest vertical structure equation of the classic tidal theory accounting for a realistic vertical temperature profile is considered. Analysis and simulation show that the well-known normal atmospheric modes (NM), which are trapped in the lower and middle atmosphere, exhibit a wave-like vertical structure with a large vertical wavelength in the thermosphere. Moreover, the reflection of these modes from the vertical temperature gradient in the lower thermosphere causes appearance of the wave-energy upward flux in the middle atmosphere, and in a linearized formulation this flux is constant above the source region. To investigate a possibility of the NM forcing by stratospheric vacillations and to consider the propagation of different PW up to the heights of the upper thermosphere, a set of runs with a mechanistic Middle and Upper Atmosphere Model has been performed. The results of the simulation show that quasi-stationary and longer-period PW are not able to penetrate into the thermosphere. The shorter-period NM and ultra-fast Kelvin wave propagate up to the heights of the lower thermosphere. However, above about 150km they are strongly suppressed by dissipative processes. The role of the secondary waves (nonmigrating tides) arising from nonlinear interaction between the primary migrating tides and quasi-stationary PW is discussed. We conclude that PW are not capable of propagating directly up to the heights of the ionospheric F2 region. It is suggested that other physical processes (for instance, the electrostatic field perturbations) have to be taken into account to explain the observed PW-like structures in ionospheric parameters. [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]

Mesosphere/lower thermosphere wind data sets from three midlatitude sites and UKMO assimilated wind data in the height range 0–55 km at 55°N were used to show the altitudinal and longitudinal variability of mean winds and planetary waves at mid-latitudes during solstices. In spite of the existence of longitudinal differences of the prevailing winds and the annual and semiannual oscillations, certain common features of the zonal wind height profiles are visible in the height range 10–100 km. The maxima of the mean annual winds and of the intensities of the annual and semiannual oscillations occur near the stratopause. In the height range 80–100 km there is an increase in the annual mean winds and in the amplitudes of the annual and semiannual oscillations; also the semiannual oscillation is larger than the annual one. Minima of the annual/semiannual oscillation amplitudes at heights of 85–95/80–85 km are accompanied by corresponding phase changes of 180 degrees in relation to those values near the stratopause. The height structure of meridional wind parameters is more complicated, with dependences on longitude and height. Longitudinal variability in the intensity of planetary waves was also found. [Copyright &y& Elsevier]

During the PSMOS Global-scale tidal variability experiment campaign of June 1–August 31, 1999, a network of radars made measurements of winds, waves and tides in the mesosphere/lower-thermosphere region over a wide range of latitudes. Clear evidence was found that fluctuations in tidal amplitudes occur on a global scale in both hemispheres, and that at least some of these fluctuations are periodic in nature. Modulation of the amplitude of the 12 h tide was particularly evident at periods of 10 and 16 days, suggesting a non-linear interaction with planetary waves of those periods to be responsible. In selected cases, the secondary waves predicted from non-linear theory could be identified and their zonal wave numbers determined. In some, but not all, cases the longitudinal structure of the secondary waves supports the theory of planetary-wave/tidal interaction being responsible for the observed tidal modulation. It was noted also that beating between a 12.4-lunar and the solar tide could produce a near 16-day modulation of the 12 h tide amplitude that is frequently observed in late summer. [Copyright &y& Elsevier]