中文摘要：

通过数值试验的方法，研究非保守系统中的基流平衡被破坏和重建过程中，产生非平衡中尺度环流与不稳定能量造成的对流关系，着重探索在形成持续时间较长、尺度较大的深厚湿对流的物理过程中，强迫与不稳定的相互作用。研究结果表明：强迫流比不稳定流小一个量级。强迫流虽然本身的量值较小，但是强迫流是不稳定流的触发机制。如果环境场具有深厚的不稳定层（垂直或倾斜方向），并且环境场强迫出一定振幅的呈上升运动的强迫流，则在0～3小时以后，将在强迫流上升运动中心激发出不稳定流上升运动中心，或使已经存在的不稳定流上升运动中心向强迫流上升运动中心移动。

英文摘要：

Slantwise convection caused by frontogenesis and moist symmetric instability also can lead to band rain. In virtual atmosphere, it is difficult to separate frontogenesis from moist symmetric instability, because they are associated with each other. In the process of deep moist convection with the characteristics of long duration and large scale, the interaction between forced and instable mesoscale convection become more complex. Based on the numerical method, the interaction between forced and instable convection in the process of the break and rebuilding of equilibrium state is discussed using mesoscale numerical-model output of Meiyu front heavy rain process in China. The instable convection is defined as the convection caused by conditional instability or conditional symmetric instability, and the ascending motion caused by the forced factor except the instable one is named as the forced convection. For moist atmosphere, the atmospheric instable factor is defined by convective condensation heat item. In theory, the ageostrophic omega equation should be used only with convective condensation heat item on the right side of the equation to compute the instable convection. But in practice, the parameterized scheme is used to compute the instable convection, the scheme is not only complex, but also with definite error. The numerical result of sensitivity test is used to resolve the instable convection. There are several kinds of reasons resulting in the forced convection, they are ageostrophic forced effect of atmospheric motion, terrain, environmental thermodynamic force and friction. The whole forced convection caused by all factors could not be computed accurately. So the mesoscale circumfluence caused by ageostrophic force is just considered, the ageostrophic omega equation only with ageostrophic force is used to compute the force convection. The MM5 mesoscale simulation system is chosen to make a numerical experiment for a typical Meiyu-front process standing from 23 to 24 June 1999. Three experiment schem