ON THE FORMATION AND THE DESTRUCTION OF THERMAL WIND IN A SIMPLE BAROCLINIC ATMOSPHERE

In this paper, the principle of the variation,of the vertical motion in the adjusting process of the Thermal wind is discussed by means of a simple two-layer baroclinic model. When the thermal wind vorticity in wind field is larger than that in temperature field, the ascending motion must accelerated, and vice versa. For the baroclinic system in the upper troposphere between 250 mb and 750 mb, the temperature field is adjusted towards wind field when.the scale of the system is smaller than a critical scale L0, and the reversed is true when the scale of the system is larger than L0. This is, demonstrated by calculated examples in which two horizontal scale are used. They are about 1000 km and 300 km respectively. In the former (1000 km), the adjustment is mainly towards the temperature field, and later is mainly towards the wind field. According to the contrast between the rate of the formation of the thermal wind and that of the destruction, we elucidate primarily the physical process of the formation of the quisi-geostrophic motion and non-geostrophic motion. Finally we applied the method proposed in present paper to examine the baroclinic instability of the long wave, and then clerify the vorticity mechanism of the baroclinic instability.