The Subpolar Front of the Japan/East Sea. Part III: Competing Roles of Frontal Dynamics and Atmospheric Forcing in Driving Ageostrophic Vertical Circulation and Subduction
The Subpolar Front of the Japan/East Sea. Part III: Competing Roles of Frontal Dynamics and Atmospheric Forcing in Driving Ageostrophic Vertical Circulation and Subduction
复制标题
日本/东海的副极地锋。
DOI：
10.1175/jpo-d-11-0154.1
复制
发表时间：
2012
影响因子：
3.5
通讯作者：
and Leif N. Thomas
中科院分区：
文献类型：
--
作者：
Yutaka Yoshikawa;Craig M. Lee;and Leif N. Thomas
本文用一个非静力数值模式研究了风应力和地面冷却对日本/东海副极地锋非地转垂直环流和俯冲作用的影响。在风和/或冷却强迫的实验中，非地转垂直环流相对于非强迫情况增强。地面冷却和风应力通过加强锋生和锋弯曲来加强环流。风通过产生内部重力波进一步加强垂直运动。顺风（即，沿着锋面射流）将表面水从锋面的密度较大的一侧输送到较轻的一侧，使其向较高分层的区域迁移，并增强锋面的垂直混合。这导致等密度柱从密度跃层的中部出露，地表水沿密度跃层沿着消减。因此，下锋面的风会增强俯冲作用，使俯冲作用下降到密度跃层的中部，而不是下部。另一方面，冷却将等密度线从更深的地方抬升到地表，从而允许流体俯冲到更深的地方。与垂直环流相反，锋面俯冲更容易被地面冷却而不是风应力所强化，因为风强迫环流的一部分（例如，内部重力波）对俯冲没有贡献。当风应力和地面冷却同时作用时，非地转垂直环流和锋面俯冲最强烈。
The effects of wind stress and surface cooling on ageostrophic vertical circulation and subduction at the subpolar front of the Japan/East Sea are investigated using a nonhydrostatic numerical model. In experiments forced by wind and/or cooling, ageostrophic vertical circulation is enhanced relative to the unforced case. Both surface cooling and wind stress intensify the circulation by enhancing frontogenesis associated with frontal meandering. Winds further strengthen vertical motions by generating internal gravity waves. Downfront winds (i.e., oriented along the frontal jet) transport surface water from the denser to lighter side of the front, causing it to migrate toward the region of higher stratification and enhancing the vertical mixing at the front. This induces outcropping of isopycnals from the middle of the pycnocline along which surface water is subducted. Hence downfront winds enhance subduction down to the middle of the pycnocline, but not beneath. On the other hand, cooling uplifts isopycnals from greater depths to the surface so that it allows for the subduction of fluid to greater depths. In contrast to the vertical circulation, frontal subduction is more intensified by surface cooling than wind stress, because part of wind-forced circulation (e.g., internal gravity wave) does not contribute to subduction. Ageostrophic vertical circulation and frontal subduction are most intense when both wind stress and surface cooling are at play.