Effects of Thermal Forcing on the Local Circulation

Many factors have impact on local circulation such as surface friction, topography, thermal forcing and so on. Attentions are paid to the spatial and temporal variation of wind, temperature, divergence and vorticity which is at the bottom of thermal forcing. Thermal forcing has effect on surface and atmosphere. In order to conduct research on the effects of thermal forcing on local circulation, based on the two dimension Bossinesq equations of mesocscale incompressibile at mospheric motion including surface heating, a set of perturbation solutions that mainly including perturbations of vertical motion, horizontal motion, pressure and temperature forced by surface heating is obtained. Then the perturbation effects on the local circulation forced by thermal heating, and temporal and spatial variations of the perturbation fields are qualitatively discussed by using dynamics method. The main conclusions are as follows: The intensity of moment turbulence is positive correlation with the thermal forcing, but in stable stratification, it is negative to stability parameter. Under the condition of fixed altitude and time, differential surface heating is beneficial to the formation of horizontal gradient of temperature or horizontal shear of wind, there is ascending motion in the heating center and sinking motion in both sides of heating center. The horizontal wind disturbance, distribution of vertical wind shear and variation of horizontal divergence resulted from surface heating are opposite to those from atmospheric heating. The distribution of horizontal vorticity is caused by surface heating, there is negative vorticity in the west side of heating center and positive in the east side. But for atmospheric heating, there is negative vorticity in both sides of heating center. The variation tendency of horizontal vorticity with time is opposite in the two kinds of heating. A simple physical model can be concluded by researching and analyzing. The horizontal gradient of temperature can be caused by the uneven heating of surface and the structure of wind can be changed, by which divergence, vorticity and vertical shear of wind can be caused. Because of the ascending motion caused by convergence of airflow in the center of heating, it is beneficial to releasing latent heat of condensation in atmosphere. The horizontal wind disturbance, distribution of vertical winds hear and variation of horizontal divergence resulted from atmospheric heating are opposite to those from surface heating. And two symmetry local vertical circulation cells are formed which are the central axes of surface atmospheric heating. The results not only strengthen people's understanding of the mechanism and the rule of local circulation, but also hold the theoretical significance leading to many local circulation problems(such as urban heat island, valley breeze, land and sea breeze and air turbulence)and the influences of thermal forcing on these local circulations.