摘要
当地形次尺度强迫的作用与显式的经典动力作用效应相当时,地形重力波拖曳力对于环流的维持,以及动量和热量通量输送的动力效应变得十分显著。这种地形次尺度拖曳作用项可通过参数化的方法,在动力方程中加入额外的小项而引入数值模式。目前成熟的地形重力波拖曳参数化方法,如第1代基于线性单波理论的参数化方案;以及侧重考虑了临界层作用等因素对拖曳力的额外贡献的第2代参数化方案,都无法有效表达风速垂直变化引起的波动应力随高度变化的特征。基于上述考虑,本文给出了一个双波参数化方案用于计算地形重力波拖曳中由线性自由传播重力波造成的波动应力的垂直分布。通过二阶WKB近似,它对由风速垂直变化引起的对波动应力的选择性临界层吸收过程和经典的临界层吸收过程做了显式处理;而在不发生临界层吸收现象的地区,则用两个单波同时在垂直方向上进行应力的传播,并利用波饱和标准进行应力耗散。进一步地在真实地形(以大别山地区为个例)条件下的测试结果表明,通过在不同理想风速廓线以及北半球冬季中纬度纬向平均风廓线下对波动应力垂直分布的计算,证明该方案确实能有效地给出应力随高度变化的特征。
When the magnitude of sub-scale ographic forcing is comparable with explicitly ordinary dynamic forcing, the drag effect reduced by ographic gravity wave is to be significant for maintaining dynamic balance of atmospheric circulation, as well as the momentum and energy transport. Such sub-scale ographic forcing should be introduced into numerically atmospheric model by the means of drag being parameterized. Furthermore, the currently mature ographic gravity wave drag parameterization, whatever the first-generation （based on lineal singlewave theoretical framework） or the second-generation drag parameterization （an important extra forcing by the contribution of critical level absorption）, they can not correctly and effetely describe the vertical profile of wave stress under the influence of ambient wind shearing. Based on aforementioned consideration, a two-wave scheme was proposed to parameterize the ographic gravity wave drag by freely propagating gravity waves. It starts with a second order WKB approximation, and treats the wave stress attenuations caused either by the selective critical level absorption or the classical critical level absorption explicitly; while in regions where critical levels are absent, it transports the wave stress vertically by two sinusoidal waves and deposits them according to the wave saturation criteria. This scheme is thus used to conduct some sample computations over the Dabie Mountain region. The results showed that the new two-wave scheme is able to model the vertical distribution of the wave stress more realistically.
出处
《气象学报》
CAS
CSCD
北大核心
2007年第5期733-743,共11页
Acta Meteorologica Sinica
基金
国家自然基金项目(40575017)
国家重点基础研究发展规划项目(973:2004CB418301)
博士点专项科研基金(2005028035)
关键词
地形重力波拖曳
双波参数化方案
临界层吸收
WKB近似
Ographic gravity wave drag （OGWD）, Two-wave parameterization of OGWD, Critical-level absorption, WKB Approximation.
