The Response of Quasigeostrophic Oceanic Vortices to Tropical Cyclone Forcing
The Response of Quasigeostrophic Oceanic Vortices to Tropical Cyclone Forcing
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DOI：
10.1175/jpo-d-11-06.1
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发表时间：
2011-10-01
影响因子：
3.5
通讯作者：
Halliwell, George R.
中科院分区：
文献类型：
--
作者：
James, Benjamin;Shay, Lynn K.;Halliwell, George R.
利用等流海洋模式研究了准地转（QG）海洋涡旋对热带气旋强迫的响应。从卡特里娜飓风期间获得的观测资料中得到的理想化的洋流和风场用于初始化该模式。研究发现，上升流响应是海洋混合层（OML）气流加速旋度的函数，而不是风应力旋度的函数。当它在气旋（反气旋）QG涡旋上转译时，在TC的眼下主要存在上升流（下升流）状态。由于下沉、深层暖水柱上的瞬时湍流夹带（弱分层）和近惯性能量的垂直弥散的综合作用，在反气旋上发生了类似1摄氏度的OML冷却。相比之下，由于上升流、紧密垂直热梯度区域（强分层）上的瞬时湍流夹带以及近惯性能量的捕获（增强了OML底部的垂直切变和混合）的综合作用，OML上发生的类似4摄氏度的冷却发生在气旋上。QG涡旋的旋转速率影响近惯性波的色散。随着气旋和反气旋的旋转增加，近惯性响应转向更有能量的频率，从而增强垂直切变和混合。tc引起的QG涡旋温度异常随时间向西传播，使冷尾流变形。因此，为了准确模拟TC诱导的OML冷却和反馈机制对风暴强度的影响，耦合的海洋-大气TC模式必须解析地转海洋涡旋位置以及热、密度和速度结构。
The response of quasigeostrophic (QG) oceanic vortices to tropical cyclone (TC) forcing is investigated using an isopycnic ocean model. Idealized oceanic currents and wind fields derived from observational data acquired during Hurricane Katrina are used to initialize this model. It is found that the upwelling response is a function of the curl of wind-driven acceleration of oceanic mixed layer (OML) currents rather than a function of the wind stress curl. Upwelling (downwelling) regimes prevail under the TC's eye as it translates over cyclonic (anticyclonic) QG vortices. OML cooling of similar to 1 degrees C occurs over anticyclones because of the combined effects of downwelling, instantaneous turbulent entrainment over the deep warm water column (weak stratification), and vertical dispersion of near-inertial energy. By contrast, OML cooling of similar to 4 degrees C occurs over cyclones due to the combined effects of upwelling, instantaneous turbulent entrainment over regions of tight vertical thermal gradients (strong stratification), and trapping of near-inertial energy that enhances vertical shear and mixing at the OML base. The rotational rate of the QG vortex affects the dispersion of near-inertial waves. As rotation is increased in both cyclones and anticyclones, the near-inertial response is shifted toward more energetic frequencies that enhance vertical shear and mixing. TC-induced temperature anomalies in QG vortices propagate westward with time, deforming the cold wake. Therefore, to accurately simulate the impact of TC-induced OML cooling and feedback mechanisms on storm intensity, coupled ocean atmosphere TC models must resolve geostrophic ocean eddy location as well as thermal, density, and velocity structures.