Subjects: Geosciences >> Space Physics submitted time 2017-01-22
Abstract： This study use the wind data from the observation of China Langfang (39°N，117°E) meteor radar during the 1 April 2012 to 31 March 2013 to investigate the features of the mesospheric and lower thermospheric mean winds within 80-100 km altitude regions. The results show that the mean zonal winds and mean meridional winds both have obviously seasonal variations. During the winter, eastward winds prevail in the MLT ranges, which is strong in mesosphere and decrease versus increasing altitude. In the summer, westward winds dominate in mesosphere, and decrease along with increasing altitude, then turn to the strong eastward in lower thermosphere. The wind evolution in the spring and autumn are the transition characters between the summer and winter. The mean meridional winds are southward in summer and northward with sometimes reversal in winter, in general. The above main seasonal variations of mean winds are captured largely by the simulation of WACCM4 model and HWM93 model. WACCM overestimates the winds, but HWM93 underestimates the winds.
Peer Review Status:
Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-03
Abstract： Gravity wave activity in the upper stratosphere is investigated using density data retrieved from the Rayleigh lidar of National Space Science Center, Chinese Academy of Sciences. Combining the Rayleigh lidar data with the wind data of National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS), we study a mountain wave observed on November 11, 2013. The parameters of this mountain wave, such as propagation direction and propagation speed, have been calculated. Gravity wave perturbations are extracted from 0.5 h×1 km density profiles. The relative density perturbations are expressed by ρ'(z)=(ρ(z)-ρ0(z))/ρ0(z), where ρ(z) is the measured atmosphere density, and ρ0(z) is the background density which is calculated by fitting the logarithmic form of whole night mean density with 4 order polynomial. The background wind data are achieved by applying a linear polynomial fitting to the NCEP-GFS wind data between 20 to 48 km altitude. Using the data extracted from the complete density perturbations structure and the background wind data, we calculate the parameters of gravity waves observed on November 11, 2013 by the gravity wave dispersion equation. The complete density perturbation structure shows an obvious phenomenon of mountain gravity wave activity. The wave phases at same altitude remain unchanged in the whole night. The perturbation structure shows that vertical wavelength is about 5.5 km but changes with altitude. A group of over-determined equations can be established by substituting the data extracted from the complete density perturbations structure and the background wind data into the gravity wave dispersion equation. And two groups of solutions are obtained by using the least squares method to solve these over-determined equations. The wind profiles in the direction of two sets of solutions have been analyzed. A critical layer (zero wind layer) which will prevent the upward propagation of mounting waves is found in the wind profile in the direction of 37.9°(or 217.9°). Finally, the gravity waves observed on November 11, 2013 propagate in the direction of 52.4° from the north to the west, with a horizontal wavelength of 5.5 km. Compared with inertia waves, there is no downward-propagating or upward-propagating phase in the density perturbation structure. At the same altitude, the phase remains unchanged in the whole night. Such kind of gravity wave perturbation structures have been often observed in winter. Density data obtained by Rayleigh lidar and NCEP-GFS wind data at Beijing are used to analyze a mountain wave parameters observed on November 11, 2013. By analysis, we obtain terrain-generated gravity waves propagating in the direction of 52.4° from the north to the west, with a horizontal wavelength of 5.5 km and average vertical wavelength of 6.0 km. ©, 2015, Science Press. All right reserved.
Peer Review Status:Awaiting Review
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