摘要
在边界层动力学中 ,涡动粘性系数是影响边界层风场结构的一个重要参数。本文利用边界层动力学中的 Ekman动量近似理论 ,给出了涡动粘性系数随高度缓变条件下的 Ekman动量近似边界层模式解 ,着重讨论了边界层的风场结构、水平散度、垂直涡度以及边界层顶部的垂直速度。结果分析表明 :与常值涡动粘性系数情况相比 ,在边界层低层随高度增加的涡动粘性系数可以导致低层边界层风速随高度迅速增加 ,即风速垂直切变增加 ,同时风速矢与地转风之间的夹角减小。惯性项作用可以导致上述作用在气旋性区域减小、而在反气旋性区域增大。随高度增加的涡动粘性系数导致水平散度绝对值、垂直涡度绝对值以及边界层顶部的垂直速度绝对值在气旋性区域减小 ,而在反气性旋区域增大。
In boundary layer dynamics,the eddy diffusivity is a important parameter for the wind structure in the planetary boundary layer.In the present study,a solution of a vertically variable eddy viscosity boundary layer model under the Ekman momentum approximation is proposed.The effect of inertial term and vertical varying eddy viscosity on the wind structure,horizontal divergence,and vertical vorticity in the boundary layer and vertical motion at the top of boundary layer are discussed in detail.In comparison with the constant eddy viscosity Ekman model,the eddy viscosity increasing with height results in the increasing of vertical wind shear and deceasing of the angle between the wind vector and x axis.The inertial term enhances these effects in the anti cyclonic and weakens in the cyclonic.The eddy viscosity increasing with height decreases the absolute values of horizontal divergence,vertical vorticity in the boundary layer and vertial motion at the top of the boundary layer.Moreover,the effect of inertial term brings on the increasing of vertical motion at the top of the boundary layer in the anti cyclonic and decreasing in cyclonic.The interaction between the eddy viscosity and inertial terms is an important process in the boundary layer dynamics.
出处
《气象科学》
CSCD
北大核心
2001年第4期433-444,共12页
Journal of the Meteorological Sciences
基金
国家重点基础研究发展规划项目 ( G1 9980 4 0 90 7)
国家自然科学基金项目 ( 4 0 0 75 0 1 0 )资助
