中层及低热层大气对局地时变热源的响应

Response of Mesosphere and Lower Thermosphere to a Localized and Time-Variable Thermal Source

采用二维交替方向隐格式(ADI),数值模拟了中高层大气对一个位于对流层高度范围的局地时变热源的响应．分析了这一过程中大气响应的能量密度,水平波数,垂直波数以及频率．模拟结果表明:响应波动携带能量向上传播,集中在较为狭窄的水平区域,该区域关于源的水平位置对称;相对于动量源驱动,热源的水平尺度对响应的水平波长决定性作用更加明显;对于高频振荡的热源,其响应的频率和源一致;响应的垂直波长(41 km)比源的垂直尺度(6 km)大得多．

By using the alternative-direction-implicit scheme, a two-dimensional fully nonlinear compressible atmospheric dynamic model is established, with which, the responses of the mesosphere and lower thermosphere to a localized and time-variable thermal source and a momentum forcing source in the troposphere are numerically simulated respectively. And then the energy density, the horizontal and vertical wavenumber and the frequency of the response are analyzed. The numerical results show that the response carrying the energy propagates from the troposphere and lower stratosphere upward to the mesosphere and lower thermosphere within a relatively narrow horizontal field which is symmetrical about the horizontal location of the heat source. The effect of the heat source upon the response is much stronger than that of the momentum forcing source. It is different in affecting the frequency, the horizontal wave length and the vertical wave length of the induced gravity wave. The horizontal wave length can be determined by the horizontal scale of the heat source, the frequency of the response is almost the same with the heat source with high frequency in the simulation, but the vertical wave length of the response is much larger than the vertical scale of the source. Usually, the longer the horizontal scale of the thermal source is, the larger the vertical wave length of the induced gravity wave.