THE FOUNDATION AND MOVEMENT OF TROPICAL SEMI-GEOSTROPHIC ADAPTATION

The breakdown and foundation of geostrophic balance is one of the important movements in the mid-and high-latitude atmosphere and oceans.In the tropical area,the value of Coriolis parameter is so small that it is difficult to satisfy the bi-geostrophic equilibrium between the pressure and velocity fields.However,in the tropical area,the zonal velocity of some motions in the atmosphere and oceans is large,so the Coriolis force is not small,geostrophic balance can exist in zonal direction,i.e.semi-geostrophic balance.Furthermore,in the dominant area of Hadley circulation in the atmosphere or the area near the ocean meridional boundary,the meridional velocity is large,so geostrophic balance can also exist in meridional direction.In this paper,the process of the dispersion of inertial gravity wave and the foundation of semi-geostrophic balance are first discussed.Second,the adjustment process between the velocity and pressure fields after adaptation is also viewed,and the scale criterion of the semi-geostrophic adaptation is discussed,i.e.for the motion with meridional scale greater than the equatorial Rossby radius of deformation,the velocity and pressure fields after adaptation change to fit the initial pressure field;on the contrary,the fields change to fit the initial zonal velocity field,and the strength of the fields after adaptation depends on the zonal scale.