北京地区重力波活动及其波谱的季节分布特性研究

Gravity Wave Parameters and Their Seasonal Variations Derived from Na Lidar Observations at Beijing

利用激光雷达对北京地区上空Na层进行持续观测,通过连续三年累积的夜间观测数据对北京地区重力波活动及其波谱进行研究.根据重力波的线性理论计算,得到北京地区上空的大气密度扰动规律、空间功率谱和时间频率谱.通过选择重力波波长在1~8 km,具有特定波长以及特定周期为60,45,25 min的重力波活动辅助研究重力波的季节变化规律,结果表明北京地区重力波大气密度扰动具有夏季大、冬季小的活动规律.结合波源与背景风场的季节性变化规律,分析得出北京上空重力波活动季节性变化的主要原因为青藏高原地形和对流因素与我国北方地区季节性背景风场共同作用的结果.

The nightly and seasonal variabiUty of gravity wave activity and spectra in the mesopause over Beijing are studied with 3 years of sodium lidar observations.Prom the linear layer density response to gravity wave forcing,the lidar data were analyzed to get the atmospheric density perturbations and their spectra.The atmospheric density perturbation,density variance for fluctuations with vertical scales between 2 and 10 km,and amplitudes of density perturbation spectra at m = 2π/8,2π/4,m = 2π/1.5,m = 2π/1,and ω — 2π/60,ω = 2π/40,2π/25 all exhibit large nightly variability as well as large seasonal variations,with the semiannual maxima occurring near the solstice.The mean RMS atmospheric density perturbation over Beijing are 5.8%,which are obviously larger in summer than that in winter and the maxima occur near the solstice.The m spectra show power law shapes,and their range of variation is between —1.97 and —3.67 with an annual mean value of—3.02,and ω spectra is between —1.06 and —2.08 with an annual mean value of —1.92,respectively.It is concluded that the reaction of the Qinghai-Tibet Plateau and the background wind may be the main reason of the gravity wave behaviors at Beijing.