低纬斜压两层模式大气半地转适应过程

利用斜压两层模式研究了赤道平面近似下的低纬热带大气适应过程。指出低纬斜压大气适应过程主要受重力惯性内波控制。通过重力惯性内波对初始非地转能量的频散，使纬向运动达到地转平衡，而经向维持非地转运动，正压模式下称为半地转平衡，斜压模式下称为半热成风平衡。通过对垂直运动方程的求解，可知，垂直运动只与重力惯性内波相联系，其产生与初始斜压位涡度无关，而只与初始时刻的垂直运动和垂直运动倾向有关，半地转适应使运动趋向水平运动。讨论了半热成风平衡的建立及其物理机制，指出由于重力惯性内波激发出垂直运动，与垂直运动相联系的水平辐合辐散调整流场和温度场之间的关系，使温压场最终达到半热成风平衡。通过对适应过程终态的分析，指出平均温度场和切变流场之间的适应方向决定于初始非半地转扰动的尺度与斜压Ｒｏｓｓｂｙ变形半径有关的特征尺度的比值，当比值大于１时，切变流场向平均温度场适应；当比值小于１时，平均温度场向切变流场适应

THE SEMI-GEOSTROPHIC ADAPTATION PROCESS WITH TWO-LAYER BAROCLINIC MODEL IN LOW LATITUDE ATMOSPHERE

In this paper,the adaptation process in low latitude is discussed by means of the two-layer barolinic model on the equator B plane,showing that the adaptation process in low latitude is mainly dominated by the internal inertial gravity wave.The initial ageostrophic energy is dispersed by the internal inertial gravity wave,and as a result,the geostrophic motion is obtained in zonal direction while the ageostrophic motion maintains in meridional direction,which can be called semi-geostrophic balance in barotropic model as well as semi-thermal-wind balance in baroclinic model.The vertical motion is determined both by the distribution of the initial vertical motion and that of the initial vertical motion tendency,but it is unrelated to the initial potential vorticity.Finally,the motion tends to be horizontal.The discussion of the physical mechanism of the semi-thermal-wind balance in low latitude shows that the achievement of the semi-thermal-wind balance is due to the adjustment between the stream field and the temperature field through the horizonal convergence and divergence which is related to the vertical motion excited by the internal inertial gravity wave.The terminal adaptation state obtained shows that the adaptation direction between the mean temperature field and the shear flow field is determined by the ratio of the scale of the initial ageostrophic disturbance to the scale of one character scale related to the baroclinic Rossby radius of deformation.The shear stream field adapts to the mean temperature field when the ratio is larger than 1,and the mean temperature field adapts to the shear stream field when the ratio is smaller than 1.