南海北部反气旋涡旋边缘的次中尺度动力过程分析

doi:10.11978/2017079

摘要/Abstract

摘要：

广泛存在于上层海洋的次中尺度过程能有效地从平衡态的中尺度地转剪切中汲取动能, 并通过非地转斜压不稳定正向串级能量至小尺度的耗散过程, 从而对海洋物质能量输运、中尺度过程变异以及混合层再层化等产生重要影响。文章利用高分辨率(500m)的区域海洋数值模式ROMS(Regional Ocean Modeling System)模拟结果, 并结合理论分析, 对南海北部冬季典型反气旋涡的次中尺度动力过程进行了初步探讨。研究结果表明, 典型中尺度涡边缘存在显著的锋面, 锋面海域强烈的水平浮力梯度能有效地减小Ertel位涡, 有利于诱发次中尺度对称不稳定(symmetric instability); 锋生作用是引起该中尺度涡边缘发生对称不稳定的主要动力机制之一。同时, 次中尺度过程及其不稳定引起的垂向次级环流显著增强了混合层垂向物质能量交换, 最大垂向速度可达95m·d^-1, 影响深度最深至80m。

关键词: 南海北部, 反气旋涡, 锋面, 次中尺度过程, 对称不稳定

Abstract:

Mesoscale energy can be effectively extracted from geostrophic flows via sub-mesoscale processes and forward cascade to smaller dissipation scales. These ubiquitous sub-mesoscale processes in the upper ocean play an important role in the transport of mass and energy, mesoscale variability and re-stratification of mixed layer. Using the high-resolution (500-m) ROMS results, we preliminarily analyze the sub-mesoscale dynamic processes of typical anticyclonic eddy in the northern South China Sea in winter. Our results show that the strong lateral buoyancy gradient at eddy periphery can efficiently reduce the Ertel potential vorticity of the front, which exacerbates frontal instabilities and is favorable for the development of symmetric instability (SI). In this case, one of the most important mechanisms is the frontogenesis for the generation of frontal SI. Furthermore, sub-mesoscale processes and associated instabilities can trigger a strong vertical secondary circulation across the front. The vertical velocity is up to 95 m·d^-1, suggesting significant vertical exchanges of mass and energy in the mixed layer.

Key words: northern South China Sea, anticyclonic eddy, front, sub-mesoscale process, symmetric instability

郑瑞玺, 经志友, 罗士浩. 南海北部反气旋涡旋边缘的次中尺度动力过程分析[J]. 热带海洋学报, 2018, 37(3): 19-25.

Ruixi ZHENG, Zhiyou JING, Shihao LUO. Analysis of sub-mesoscale dynamic processes in the periphery of anticyclonic eddy in the northern South China Sea[J]. Journal of Tropical Oceanography, 2018, 37(3): 19-25.

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