风生边界急流稳定性的渐近理论

Asymptotic theory of the wind-driven boundary jet's stability

观测表明,当冬季盛吹北风时,在南中国海西边界附近将形成一支向南的急流,在一定条件下这支急流可弯曲成波动甚至形成涡旋.本文应用等值浅水模式,采用截断模方法,分析了急流的稳定性,并给出急流上不稳定波出现的条件.分析表明只有当向南的风生急流很强很窄时,由变性的Kelvin波和风应力强迫出的地形Rossby波在长波波段耦合而出现不稳定,不稳定波在波长约200 km时向北传播的相速度约为0.2 m.s-1,波振幅增长到e倍所需的时间约1.5天.分析进一步表明,夏季向北的风生流在海洋的西边界附近是稳定的.这些结果在一定程度上解释了观测结果.

In observation, there is a southward jet in the western boundary of the South China Sea （SCS）, when the north wind is strong in winter. The jet stream can bend into wave, even eddy under certain conditions. In the text, we used equivalent shallow water model and truncated model method to analyse the stability of the jet, and pointed out the conditions of the appearing of instable wave. The results indicate that when the southward wind-driven current is strong and narrow, the metamorphic Kelvin wave and wind stress forced ＂topographic Rossby-wave＂ can couple into instable wave in the long-wave period. When the wavelength of the instable wave is about 200 km, it spreads northward at a speed about 0.2 m· s^-1, and the amplitude of the wave can increase to e multiples in about 1.5 days. Further analyses indicate that the northward wind-driven current in the western these conclusions. boundary of the ocean is stable in summer. The observation can partly be explained by