长江口外低盐水团发展的正压不稳定机制分析

针对长江冲淡水扩展区域低盐水团现象,开展正压不稳定机制研究。基于1977年夏季低盐水团的演变特征分析,将初始形成的低盐水团看成小扰动,建立小扰动方程描述低盐水团运动,采用WKBJ方法求解小扰动方程,讨论了快波过程(重力惯性波)和慢波过程(余流作用)对低盐水团的影响,并给出了受慢变波包影响的能量演变方程。研究表明,快波过程对低盐水团基本没影响,低盐水团从口门向口外东北海域运动过程中,由于水深加大,慢波过程有利于低盐水团发展。

Barotropic instability mechanism analysis to development of low-salinity water lenses outside the Changjiang Estuary

Barotropic instability mechanism analysis was carried out to research the dynamic mechanism of the low-salinity water lenses (LSWL) in the expansion of the Changjiang diluted water (CDW). Based on the analysis of the LSWL’s character in 1977 summer, the initial LSWL was taken as small disturbance, and its equation founded to describe the motion of LSWL. The solution of the equation was obtained by WKBJ method, and was used to discuss the impact of the quickly varying wave (namely inertial-gravity wave) and the slowly varying wave(namely residual current) on LSWL. And the equation of energy evolution was founded, which was controlled by slowly varying wave packet. The main conclusion is that the quickly varying wave makes negligible influence on LSWL, but the slowly varying wave is helpful for the develop ment of LSWL because of depth increase when LSWL moves from the river mouth to the northeast.