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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. [ABSTRACT FROM AUTHOR]

Abstract: Piecewise trend analysis is applied to midlatitude mesosphere/lower thermosphere winds over Europe and Canada. In summer, there are similar trends in each time series of prevailing winds. The zonal prevailing winds in winter show partly opposite behavior at different longitudes, which may be explained by a stationary planetary wave (SPW) influence. Differences between Collm (52°N, 15°E) and Obninsk (55°N, 37°E), both in Europe, are correlated with SPW variability at the interannual time scale, and with tropospheric circulation at the decadal time scale. There are also hints that summer zonal prevailing winds are connected with Southern Hemisphere planetary waves at long time scales. The long-term variation of semidiurnal tidal (SDT) amplitudes corresponds with that of the zonal prevailing wind in a sense that several joint breakpoints of trends are visible. Obninsk and Collm SDT amplitudes show, however, an out-of-phase variability on the decadal time scale. [Copyright &y& Elsevier]

Abstract: A possible planetary wave (PW) coupling between the stratosphere and ionosphere by the modulation of gravity waves (GW) is studied using midlatitude atmospheric datasets from 2002 to 2008. Information of GW is retrieved from space-based SABER temperature profiles by extracting the potential energy for vertical wavelengths shorter than 6km. For calculating stationary and travelling proxies of wave activity the data are arranged to a daily evenly spaced 3-dimensional basis. From temperature and potential energy fields direct and indirect (modulation) indices of PW activity are obtained between 30 and 130km. From the comparison with stratospheric PW, analysed from MetOffice reanalyses, and ionospheric PW type oscillations (PWTO) from GPS-TEC data, a possible coupling process is derived. The results reveal a potential connection between the stratosphere and ionosphere by PW activity around solar maximum (2002–2005) caused by the modulation of GW at midlatitudes. [Copyright &y& Elsevier]

Abstract: This paper presents a new method to estimate the meteoroid mass from specular meteor observations. The basis of this method is the ability of a standard meteor radar to measure meteoroid head velocity, the height of detection, the source radiant (on a statistical basis) and the electron line density in the specular point. The electron line density can be related to the mass ablation rate by applying an ionization efficiency model. Selecting potential meteoroids from the Geminid meteor shower according to their source radiant and velocity distribution and combining all of these measurements with a numerical single body meteor ablation model permits to compute the meteoroid mass, deceleration and temperature in the specular point. The pre-atmospheric properties of an average meteoroid are estimated by fitting the single body ablation model to the estimates of the meteor parameters in the specular points. [Copyright &y& Elsevier]

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: 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 90–92km 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. [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]

The theory of atmospheric normal modes (ANMs) predicts the existence of relatively short-period gravity-inertia ANMs. Simultaneous observations of surface air-pressure variations by barometers at distant stations of the Global Geodynamics Project network during an interval of 6 months were used to detect individual gravity-inertia ANMs with periods of ∼2–5 h. Evidence was found for five ANMs with a lifetime of ∼10 days. The data of the stations, which are close in both latitude and longitude, were utilized for deriving the phases of the detected ANMs. The phases revealed wave propagation to the west and increase of zonal wavenumbers with frequency. As all the detected gravity-inertia ANMs are westward propagating, they are suggested to be generated due to the breakdown of migrating solar tides and/or large-scale Rossby waves. The existence of an ANM background will complicate the detection of the translational motions of the Earth's inner core. [ABSTRACT FROM AUTHOR]

Abstract: For the investigation of meteoroid properties the measurement of the electron line density in meteor ambipolar plasma trails is an important parameter, which becomes accessible by a radar calibration. Radars operating in the frequency range between 20 and 50MHz are also sensitive to extraterrestrial radio waves. Depending on the geographic position and beam tilt each system observes a characteristic pattern of cosmic emissions, which can be considered to be Gaussian noise. This work demonstrates the possibilities to perform a radar calibration for standard commercial all-sky meteor radars using a delay line method and a calibrated noise source. Additionally, we also used the cosmic noise sources to estimate the impact of the antenna pattern and potential losses of the hardware (e.g. cables, connectors). The calibrated radio noise measurements are compared to a reference by mapping the Collm radar beam pattern on a sky noise maps available in the literature. [Copyright &y& Elsevier]

Abstract: The zonally averaged UK Meteorological Office (UKMO) zonal mean temperature and zonal winds for the latitudes 8.75°N and 60°N are used to investigate the low-latitude dynamical response to the high latitude sudden stratospheric warming (SSW) events that occurred during winter of the years 1998–1999, 2003–2004 and 2005–2006. The UKMO zonal mean zonal winds at 60°N show a short-term reversal to westward winds in the entire upper stratosphere and lower mesosphere and the low-latitude winds (8.75°N) show enhanced eastward flow in the upper stratosphere and strong westward flow in the lower mesosphere during the major SSW events at high latitudes. The mesosphere and lower thermosphere (MLT) zonal winds acquired by medium frequency (MF) radar at Tirunelveli (8.7°N, 77.8°E) show a change of wind direction from eastward to westward several days before the onset of SSW events and these winds decelerate and weak positive (eastward) winds prevail during the SSW events. The time variation of zonal winds over Tirunelveli is nearly similar to the one reported from high latitudes, except that the latter shows intense eastward winds during the SSW events. Besides, the comparison of daily mean meridional winds over Tirunelveli with those over Collm (52°N, 15°E) show that large equatorial winds are observed over Tirunelveli during the 2005–2006 event and over Collm during the 1998–1999 events. The variable response of MLT dynamics to different SSW events may be explained by the variability of gravity waves. [Copyright &y& Elsevier]

Abstract: The coupling of the neutral atmosphere and the ionosphere through planetary waves (PW) (zonal wavenumber 0–5) is investigated by spherical harmonic analyses of the ionospheric total electron content (TEC). These analyses detect mean variations, standing and travelling waves which are assumed to be signatures of PW. Database used for TEC analyses are 3 years of hourly TEC maps covering the higher middle and polar latitudes. They are regularly produced by DLR Neustrelitz. The obtained results are compared with PW analyses using NCEP/NCAR and Met Office stratospheric reanalyses. Case studies show that signatures of PW occur simultaneously in the middle atmosphere and ionosphere. [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 measurements from the low-orbit satellite GPS/MET in the atmosphere at 2–35 km altitudes are used to obtain global distributions of mesoscale variances of the radio wave refraction index (as a measure of dry temperature). Individual refraction index and dry temperature profiles are smoothed using second order polynomial approximations within layers of 5–10 km thickness centered at different altitudes. The refraction index deviations from the smoothed values and their variances are obtained for each profile and are averaged for each month of the year during the GPS/MET experiment during the years 1995–1997. Latitude–longitude and latitude–height distributions of the refraction index variances show inhomogeneous structures. Locations and latitude distributions of the maximum and minimum values of the variance depend on altitude and month of year. The reasons for the small- and mesoscale refraction index perturbations in the troposphere–stratosphere may be mesoscale turbulence and internal gravity waves. The magnitudes of the refraction index variances are larger in the regions of tropospheric jet streams and of equatorial deep convection. [Copyright &y& Elsevier]

Abstract: The horizontal wind data from the standard version of Canadian Middle Atmosphere Model Data Assimilation System (CMAM-DAS) have been analyzed to obtain the diurnal wind structures in the mesosphere. In the standard version of CMAM-DAS, meteorological observations from radiosondes, aircraft, surface measurements, and satellites are assimilated only in the troposphere and stratosphere (below 1-hPa) with no increments applied in the mesosphere. Results for the years 2006–2008 are being used here as part of the Canadian International Polar Year (IPY) program and the Canadian Network for the Detection of Atmospheric Change (CANDAC) Research Program. The CMAM-DAS shows good overall agreement with radar observations for the seasonal characteristics of the diurnal tides at single stations from low-middle latitudes. The most prominent nonmigrating diurnal tides revealed by the CMAM-DAS winds at 88km include the westward propagating component with zonal wavenumber 2 (DW2), the standing oscillation (D0), and the eastward propagating wavenumbers 3 (DE3) and 2 (DE2). A detailed discussion of the latitudinal and seasonal variations and Hough modes is provided for these predominant nonmigrating components and the migrating tide (DW1). The modeled nonmigrating diurnal tides, on both monthly (60-day windows) and annual time scales, are generally in good agreement with those determined from TIDI (TIMED Doppler interferometer) and from UARS-HRDI (High Resolution Doppler Imager)/WINDII (Wind Imaging Interferometer). This work provides further evidence for the tidal forcing from below. [Copyright &y& Elsevier]

Abstract: Internal gravity waves (IGWs) over Kharkiv (49°30′N, 36°51′E) have been studied by using an automatic goniometer of a meteor radar (AG MR), with its antenna directed to the East. The AG MR carries out Doppler measurements of the radial drift velocity and the position of the reflecting area of meteor trails. In order to obtain information about IGW parameters, an algorithm was used that processes the AG MR wind data by dividing the measured volume into several sub-volumes, and by carrying out wavelet analysis of wind variations in these areas. Results of 1 year (1987) of AG MR data show a good qualitative correspondence with literature results. There is an increase of IGW activity during the change of the zonal background wind in spring and autumn. It was found that the mean IGW horizontal phase velocity and predominating horizontal propagation direction change with season. However, the mean period (1.5h), the dominant amplitude (∼30m/s) and the vertical phase velocity do not strongly vary in the course of the year. The mean vertical and horizontal wavelengths were found to be 40 and 250km, respectively. [Copyright &y& Elsevier]

Abstract: Five years of global temperatures retrieved from radio occultations measured by Champ (Challenging Minisatellite Payload) and SAC-C (Satelite de Aplicaciones Cientificas-C) are analyzed for gravity waves (GWs). In order to separate GWs from other atmospheric variations, a high-pass filter was applied on the vertical profile. Resulting temperature fluctuations correspond to vertical wavelengths between 400m (instrumental resolution) and 10km (limit of the high-pass filter). The temperature fluctuations can be converted into GW potential energy, but for comparison with parameterization schemes GW momentum flux is required. We therefore used representative values for the vertical and horizontal wavelength to infer GW momentum flux from the GPS measurements. The vertical wavelength value is determined by high-pass filtering, the horizontal wavelength is adopted from a latitude-dependent climatology. The obtained momentum flux distributions agree well, both in global distribution and in absolute values, with simulations using the Warner and McIntyre parameterization (WM) scheme. However, discrepancies are found in the annual cycle. Online simulations, implementing the WM scheme in the mechanistic COMMA-LIM (Cologne Model of the Middle Atmosphere—Leipzig Institute for Meteorology) general circulation model (GCM), do not converge, demonstrating that a good representation of GWs in a GCM requires both a realistic launch distribution and an adequate representation of GW breaking and momentum transfer. [Copyright &y& Elsevier]

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]

Abstract: 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 (1.1–1.4m/s/year) in the earlier years of measurements become smaller (about 6 times) in the beginning of the 1970s. [Copyright &y& Elsevier]

A network of 15 northern hemisphere radars has been used to measure horizontal winds in the mesosphere and lower thermosphere during the PSMOS campaign of Summer 1999. The radars are sited at latitudes ranging from 21°N to 75°N and longitudes from 142°E to 157°W. The data were examined to investigate the Northern Hemisphere structure of the quasi-2-day planetary wave during the interval June–August. The amplitude of the 2-day wave was found to exhibit great day-to-day variability. In particular, significant periodic fluctuations in amplitude occurred with periods of 8–10 and 14–17 days. These modulations were strongest in July and largely absent in June and August. In July, the wave activity can be resolved into three westward-propagating waves with zonal wave numbers of 2, 3 and 4. The periods associated with these wave numbers were 53–56, 48–50 and 42–43 h, respectively. The simultaneous presence of at least two spectral components with periods close to each other may serve to explain the observed amplitude modulations as a result of a beating between different spectral components. An earlier analysis of the planetary-wave field during this interval has revealed a westward propagating ∼16-day wave with zonal wave number 1 (Journal of Atmospheric and Solar-Terrestrial Physics 64 (2002b) 1865–1896). A non-linear interaction between this ∼16-day planetary wave and the (3,0) Rossby-gravity mode (the 2-day-wave) provides a possible mechanism to generate the above ∼42 h/wavenumber 4 wave and the ∼55 h/wavenumber 2 waves as sum and difference secondary waves. A bispectral analysis was used to further investigate non-linear interactions between members of the planetary-wave field and suggested a number of interactions occur within the planetary-wave field, but that some of the interactions also involve the non-migrating diurnal tide with zonal wavenumber 6. [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]

Observations from 2 optical ground stations and 3 MF radars at high and mid-latitudes have been combined to describe “springtime transitions” in atomic oxygen and the mesopause wind fields and waves for eight years (1991–1998). The typical signature in the Stockholm (60°N, 20°E) OI 558 nm ‘green-line’ emission involves a rapid (circa) 2-days rise in the nighttime value by factors of 2 or so, with a subsequent decrease by factors of 3–10. There is considerable inter-annual variability in these green-line emissions, and also the hydroxyl airglow (intensities and temperatures) at Bear Lake Observatory (Utah, 42°N, 115°W), but the 6–8 year means do show a characteristic airglow “springtime transition” (AST) near the end of March. MF radars from Tromsø (70°N, 19°E), Juliusruh (55°N, 13°E) and Saskatoon (52°N, 107°W) demonstrate springtime reversals in the mean (daily) zonal winds at 85–95 km, both annually and in 8 year means, at times near the airglow “transitions”. The “tongue” of easterlies (near March 30) is a long-established feature of mesopause dynamics, and clear indications of associated changes in tides and gravity wave fluxes are also presented.The TIME-GCM is also used to investigate the characteristics of the airglow and winds during the interval associated with the AST events. Useful similarities with the observed variations are demonstrated. [Copyright &y& Elsevier]

Observations of mean winds and semidiurnal and diurnal tides in the mesosphere/lower-thermosphere (MLT) region were made during the 3-month Planetary-Scale Mesopause Observing System Summer 1999 campaign. Data from 22 ground-based radars (and from two other instruments with measurements for the same period but in 1998) allow us to investigate the ability of the GSWM-00 to simulate the solar tides in the mesopause region (90–95 km). Here we have found that the GSWM-00 provides an increasingly reasonable estimate of most of the tidal characteristics in the MLT region. However, the representation of the 24 h tide appears superior to that of the 12 h tide. Some of these discrepancies are studied in detail. In particular, the observations reveal significant 12 h tidal amplitudes at high latitudes in the Northern Hemisphere summer. There is evidence for relation between the longitudinal variability of the mean zonal wind and the tidal characteristics seen from the radar wind measurements in the summer middle latitudes and a quasi-stationary planetary wave with zonal wave number one. [Copyright &y& Elsevier]