线性准地转模型中基本流和辐射冷却对感热加热强迫的副热带高压形态的影响

The effect of basic flow and radiative cooling on the shape of subtropical high forced by sensible heating in a linear quasigeostrophic model

通过求取定常线性准地转位涡模式的数值解,研究了感热型垂直非均匀分布的冷、热源强迫所激发的副热带环流的结构特征,讨论了副热带背景风场和洋面辐射冷却对洋面副热带高压"三角形偏心"结构形成的重要作用。结果表明,基本流对感热加热强迫的副热带环流有重要影响,当基本流为常数时,感热加热强迫的气旋和反气旋主要集中在对流层中下层,且地面系统远强于中高层。当基本流为非常数时,其经向切变能改变气旋和反气旋中心的经向位置,使它移至0风速所在纬度附近;其垂直变化加强了中高层气旋和反气旋,中心位于对流层上层,与南亚高压的位置基本一致。研究结果还表明,在大洋东部洋面辐射冷却与副热带地区背景风场的共同作用下,形成了洋面副热带高压特有的"三角形偏心"结构。副热带高纬度的西风使感热强迫的洋面副热带高压东移,低纬度的东风使其西移,形成东北—西南走向的"平行四边形"结构,且中心位于大洋西部。大洋东部强洋面辐射冷却激发的洋面反气旋加强了大洋东部的副热带高压,使其中心东移至大洋东部,从而表现出东北—西南走向的"三角形偏心"结构。

The configuration of the subtropical circulation forced by sensible heating is studied using a linear quasigeostrophic model. The impacts of subtropical background zonal flow and radiative cooling on the formation of triangular off-centered configuration of the surface anticyclone are discussed. Results show that when the basic flow is constant, cyclones and anticyclones forced by sensible heating are mainly situated in the middle and lower troposphere and the amplitude at surface is much stronger than that in the middle and upper layers. When the basic flow is not constant, the meridional shear of basic flow can change the meridional locations of the forced cyclone and anticyclone centers lying approximately where the zero zonal wind is located. The vertical shear of basic flow strengthens the upper layer anticyclone, makes it stronger than the surface anticyclone, and the anticyclone center is located in the upper troposphere, which is similar to the South Asia High. In addition, it is found that the surface anticyclone forms when long-wave radiative cooling in the eastern Pacific Ocean and the basic flow of the subtropical area are both considered.Subtropical westerlies in higher latitudes make the surface anticyclone move eastward, and subtropical easterlies in lower latitudes lead to its westward moving. As a result, the parallelogram surface anticyclone is forced extending from northeast to southwest and its center is situated in the western Pacific Ocean. Furthermore, radiative cooling intensifies the surface anticyclone in the eastern Pacific Ocean and causes its center to move eastward. As a result, the triangular and off-centered configuration of the surface anticyclone appears.