地形对长波和超长波不稳定发展的影响

图3.2.1—3.2.5表示了地形对长波和超长波移动和发展影响的一般规律。如以地形脊对东移西风冷槽的影响为例,当地形相当涡度和扰动涡度的振辐比a_m/a_(20)较小时,在它越过地形脊时,首先流场槽减弱而温度槽加强,减弱的流场槽以较快的速度移动,而温度槽则相对减慢,越过地形脊后,流场槽又重新增强。 我们根据地形的影响,初步讨论了一锢囚气旋在向风坡填塞,在背风坡又重新产生的物理过程。超长波的斜压不稳定的不能发展,是由于温度场东进和流场西退造成的。根据地形脊对超长波脊移动的影响,可以推测,在两个地形超长波脊之间的地区,最有利于超长波脊的不稳定发展。阻塞脊出现频数的地理分布的观测结果和理论推测有很好的一致性。

THE MOUNTAIN EFFECTS ON THE BAROCLINIC INSTABILITY OF THE LONG AND ULTRA-LONG WAVES IN THE ATMOSPHERE

The general rules about the mountain effects on the movement and development of the long and ultra-long wayes are shown in Fig.3.2.1-3.2.5.When a westerly cold trough moves eastward over a mountain, if, a_m/a₂, the amplitude ratio of the topographic equivalent vorticity to its wind field vorticity, is relatively small, its amplitude damps in wind field and amplifys in temperature, and its wave speed in wind field is faster than that in temperature field. As it has crossed the ridge of the mountain, its wind and temperature change inversly.The physical process of the cyclo-benesis in the lee side is discussed in some details. In the situation without the mountain, the mean wind field of the ultra-long waves generally westward,but the shear wind and temperature field moves generally eastward. It is the reason why the ultra-long wave is not so baroclinic unstable as the long wave.It is deduced theoretically that the ridges of the ultra-long waves are favorable to amplify between two topographic ridges with same scale, and this deduction is well consistent with the geographic distribution of the observed frequency of the blocking ridges, which is shown in Fig.5.2.