平衡流形成的机制与锋生

利用最小能量原理讨论了非地转流经过调整后的平衡态的情况。对于两维模型来说，不平衡流通过调整获得的平衡终态依赖于初始不平衡场的分布特点。如果不平衡流的初始位涡是非均匀的，则其通过适应过程而达到的平衡状态不一定满足热成风关系；对于初始位涡是均匀的或为零的不平衡流来说，如果初始密度的水平变化不是非常显著，则运动最后可以达到热成风平衡状态，反之，最后的平衡态则不满足成风关系，对于这种情况，我们利用广义动量坐标系进行了详细讨论。

Mechanism of balanced flow and frontogenesis

The final balanced state of an initial unbalanced flow is discussed with the same method as Vallis (1992). For the two-dimensional, inviscid, rotating and nonlinear model, the final state of the flow depends on the initial conditions. If the initial potential vortcity of the flow is non-uniform, the final state is not necessarily geostrophic. However, for the zero and uniform potential vorticity flow, the final state will satisfy the thermal wind relation when the length scale of the initial disturbance is large enough. Otherwise,discontinuity will occur in the geostrophic solution. In this case, the final balanced state will not be geostrophic any longer and an extended momentum coordinate is introduced to overcome the multi-value problem.