海洋背景涡度对台风康森引起的近惯性波的影响研究

THE INFLUENCE OF OCEAN BACKGROUND VORTICITY ON NEAR-INERTIAL WAVES INDUCED BY TYPHOON CONSON

近惯性波是海洋中普遍存在的一种内波,它在海洋中的传播和耗散受到背景涡度的影响。基于混合坐标海洋模型(hybrid coordinate ocean model,HYCOM)再分析数据,研究了海洋背景正、负涡度对台风康森在南海引起的近惯性波的不同影响。结果表明:负涡度能捕捉并促进近惯性能量向海洋深层的传播,可传播到1200 m以深;而正涡度则阻碍近惯性能量的下传,使其主要集中在海洋上层500 m以内。负涡度区域能维持较强的近惯性能量10 d以上,而正涡度区域内的近惯性能量维持时间在1周左右。负涡度区域内的近惯性波由第二和第三模态主导,而正涡度区域内的近惯性波由第一和第二模态主导,导致海洋内部(500~1000 m)负涡度区域内的近惯性波剪切比正涡度区域内的近惯性波剪切强1~2个量级。波射线模型模拟结果显示,近惯性波在负涡度区域边缘发生反射,进而被负涡度区域捕获;而正涡度区域内的近惯性波有加速远离源地的趋势。上述结果进一步说明,海洋背景负涡度能增强近惯性能量的垂向传播,而正涡度则促进了近惯性能量的水平传播。

Near-inertial waves(NIWs)are a type of internal waves,and which are ubiquitous in the global ocean.The propagation and dissipation of NIWs are affected by the background vorticity.Based on the hybrid coordinate ocean model(HYCOM)reanalysis data,we studied the different effects of positive and negative background vorticities on the NIWs induced by Typhoon Conson in the South China Sea.Results show that the negative vorticity can capture and promote the propagation of near-inertial energy to the deep ocean(exceeding 1200 m depth).However,the positive vorticity inhibits the downward propagation of near-inertial energy,making it concentrated mainly within the upper 500 m.Strong near inertial energy in the negative vorticity region can last for more than 10 days,while that in the positive vorticity region only lasts only about a week.The NIWs in the negative vorticity region are dominated by the second and third modes,while those in the positive vorticity region are dominated by the first and second modes.As a result,the shear caused by NIWs in the negative vorticity region is 1~2 orders of magnitude stronger than that in the positive vorticity region at 500~1000 m depth.The simulation results of the ray-tracing model show that the NIWs are reflected at the edge of the negative vorticity region and then are captured by the negative vorticity region.In contrast,the NIWs in the positive vorticity region tend to accelerate away from the source.These results further indicate that the negative background vorticity enhances the vertical propagation of near-inertial energy,while the positive vorticity promotes the horizontal propagation of near-inertial energy.