中文摘要：

利用子午工程海南激光雷达对我国海南地区上空进行持续观测,通过3年的累积观测数据对我国低纬度地区重力波活动的季节分布特性进行研究,依据重力波线性理论对海南地区上空的大气密度扰动规律、空间功率谱及时间频率谱进行分析,并通过选择波长在1km至8km范围内具有特定波长以及具有波动周期为60 min至25min的特定频率的重力波辅助研究大气密度扰动的季节变化规律,总结得出海南地区重力波活动具有夏季大、春秋季小、而冬季依然频繁的季节性分布规律.结合海南地区特殊的地理位置与当地季节性气候特征分析得出海南地区上空重力波活动季节性变化的可能原因为青藏高原地形及我国南海地区存在的热带强对流与赤道潜流共同作用的结果.

英文摘要：

Sodium lidar is recognized as a useful tool to investigate gravity wave（GW）which influences the circulation,structure and composition of middle and upper atmosphere notably.For further understanding GW and their characteristics,more sufficient observational data within global models,especially those at low latitude are extremely expected.Meanwhile,long-term observations are also quite helpful for the GW analysis.As one part of Meridian Project,the observational Na lidar system at Hainan（19.50°N,109.1°E）employed the double wavelengths laser beam,which is consists of three channels for Mie scattering,Rayleigh scattering and broadband sodium fluorescence.A pulsed Nd：YAG laser was rebuilt to trigger off two green laser beams simultaneously,one of which was 532 nm and used to excite the Mie and Rayleigh scattering,and the other laser beam pumped by apulsed dye laser was about 589 nm and with 30 mJ per pulse.Resonant fluorescence from the sodium layer was received by a Cassegrain telescope with a primary mirror of 1000 mm diameter.The lidar profiles are stored automatically in a computer.The temporal and spatial resolution was about167 sand 96m,respectively.Seasonal variations of the GW activity and their spectra at Hainan were studied with comparison to the previous reports and the predictions of theories of GW saturation and dissipation.The seasonal variations of GW activity and characteristics spectra at Hainan are mainly presented as follows：（1）The mean RMS atmospheric density perturbation over Hainan are 5.63 %,which at solstice are obviously larger than that near the equinox.And the GW activity in winter is still active,which are quite different from those reports at the middle latitude area.（2）Due to the linear theory,the mspectra were calculated which show power law shapes and their range of variation were between-2.14and-3.56 with an annual mean value of-2.93.The calculatedωspectra were between-1.22and-2.36 with an annual mean value of-1.80,respectively.（3）The amplitudes of atmospher