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Savenkova E.N.,Russian State Hydrometeorological University | Kanukhina A.,Russian State Hydrometeorological University | Pogoreltsev A.I.,Russian State Hydrometeorological University | Merzlyakov E.G.,Institute for Experimental Meteorology
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2012

The interannual variability of the springtime transition date of the stratospheric circulation is analyzed on the basis of the data assimilated in the UK Met Office and NCEP/NCAR models. As a proxy for the zonal mean flow we use the geostrophic wind calculated at 65.7. N from geopotential heights of the 10. hPa pressure level. The results show that the springtime transition date depends on the planetary-wave activity in the stratosphere and there is a tendency to the later date with a rate of about 4 days per decade. The significant correlation between the interannual variability of the spring transition date and amplitudes of stationary planetary wave with zonal wave number 1 is found. A noticeable dependence of the breakup date on the NAM index and the QBO phase is observed. © 2011 Elsevier Ltd.

Chang L.C.,University of Colorado at Boulder | Ward W.E.,University of New Brunswick | Palo S.E.,University of Colorado at Boulder | Du J.,University of Cambridge | And 16 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2012

In this study, ground-based observations of equinox diurnal tide wind fields from the first CAWSES Global Tidal Campaign are compared with results from five commonly used models, in order to identify systematic differences. WACCM3 and Extended CMAM are both self-consistent general circulation models, which resolve general climatological features, while TIME-GCM can be forced to approximate specific conditions using reanalysis fields. GSWM is a linear mechanistic model; while GEWM is an empirical model derived from ground-based and satellite observations. The models resolve diurnal tides consistent in latitudinal structure with observations, dominated by the upward propagating (1,1) mode. There is disagreement in the magnitudes of the tidal amplitudes and vertical wavelengths, while differences in longitudinal tidal variability indicate differences in the nonmigrating tides in the models. These points suggest inconsistencies in model forcing, dissipation, and background winds that must be examined as part of a coordinated effort from the modeling community. © 2010 Elsevier Ltd.

Liu R.Q.,University of Leipzig | Liu R.Q.,Nanjing University of Information Science and Technology | Jacobi C.,University of Leipzig | Hoffmann P.,University of Leipzig | And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2010

A piecewise linear model is developed to detect climatic trends and their structural changes in time series with a priori unknown number and positions of breakpoints (BPs). The departure (i.e., the initial noise term) of trends from time series is allowed to be interpreted by the first- and second-order autoregressive models. The goodness of fit of candidate models, if the residuals are accepted as normally distributed white noise, is evaluated using the Schwarz Bayesian Information Criterion (BIC). The uncertainties of all trend parameters are estimated using the Monte-Carlo method. The model is applied to the mesosphere and lower thermosphere (MLT) winds obtained at Collm, Germany, during 1960-2007. A persistent increase after ∼1980 of the zonal prevailing wind is observed in all seasons and hence in the zonal annual mean based on the primary models. Trends of the meridional prevailing wind are different for different seasons. Several major trend BPs are identified in the annual mean zonal and meridional winds according to BIC. However, in view of the large wind variability before the late 1970s, alternative models are considered. This provides four additional minor breaks. In some cases, the initial noise must be further interpreted by autoregressive models, suggesting that other unidentified factors may also play a role. © 2010 by the American Geophysical Union.

Merzlyakov E.G.,Institute for Experimental Meteorology | Jacobi C.,University of Leipzig | Solovjova T.V.,Institute for Experimental Meteorology
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2015

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. © 2014 Elsevier Ltd.

Jacobi C.,University of Leipzig | Hoffmann P.,University of Leipzig | Liu R.Q.,Nanjing University of Information Science and Technology | Merzlyakov E.G.,Institute for Experimental Meteorology | And 3 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2012

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. © 2011 Elsevier Ltd.

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