利用瑞利激光雷达观测北京地区上平流层地形重力波活动

本文利用中国科学院空间科学与应用研究中心的瑞利激光雷达首次观测到了平流层地形重力波活动的现象,并结合美国国家环境预报中心(NCEP)的全球预报系统(GFS)的风场数据分析了该地形重力波的基本参数.与惯性重力波相比较,地形重力波的密度扰动没有下传的相位,在同一高度上,其扰动相位保持不变.北京空间科学与应用研究中心瑞利激光雷达自2012年开始观测实验以来,已经观测到多起地形重力波活动事件.本文以2013年11月11日的观测数据为例,研究北京上空的地形重力波活动,并结合GFS风场数据分析了北京上平流层地形重力波的波长、传播方向、传播速度等参量.通过分析得到在2013年11月11日北京上空存在一列传播方向为北偏西52.4°,水平波长为5.5 km,平均垂直波长约为6.0 km的地形重力波.

Terrain-generated gravity waves in the upper stratosphere detected by Rayleigh lidar

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.