Tropical Cells and a Secondary Circulation near the Northern Front of the Equatorial Pacific Cold Tongue
Tropical Cells and a Secondary Circulation near the Northern Front of the Equatorial Pacific Cold Tongue
复制标题
DOI：
10.1175/2010jpo4366.1
复制
发表时间：
2010-09-01
影响因子：
3.5
通讯作者：
Kessler, William S.
中科院分区：
文献类型：
--
作者：
Perez, Renellys C.;Cronin, Meghan F.;Kessler, William S.
用船载测量和模式描述了赤道太平洋中部经向垂直热带气旋(TCS)的平均结构和与冷舌北部锋面相关的次生环流。锋面的形状被热带不稳定波(TIW)的传播所缠绕。当在以北部锋面瞬时位置为中心的坐标系中平均速度时，测量结果显示表面锋面以北的气流(锋面附近的辐合流)出现近地表极小值。这种辐合和推断的下沉运动延伸到地面混合层以下，随深度向极地倾斜，并以辐散和上升流区域为经向边界。同样，模式显示，平均而言，地面冷舌水向锋区北移并潜入倾斜锋面以下，而锋面以北的次表层水则向南向锋面上移，然后在表层混合层中向北移动。结果表明，平均准绝热次级环流不是随锋面迁移的冻结场，而是高度依赖于锋面位相的冻结场：锋面向南移位时，锋面暖侧倾向于南下涌流，锋面向北移位时，锋面冷侧倾向于向北向下涌流。因此，当在地理坐标中平均时，观测到的和模拟的TCS似乎是赤道不对称的，并且在平均锋面附近几乎没有显示出二次环流的痕迹。
Shipboard measurements and a model are used to describe the mean structure of meridional-vertical tropical cells (TCs) in the central equatorial Pacific and a secondary circulation associated with the northern front of the cold tongue. The shape of the front is convoluted by the passage of tropical instability waves (TIWs). When velocities are averaged in a coordinate system centered on the instantaneous position of the northern front, the measurements show a near-surface minimum in northward flow north of the surface front (convergent flow near the front). This convergence and inferred downwelling extend below the surface mixed layer, tilt poleward with depth, and are meridionally bounded by regions of divergence and upwelling. Similarly, the model shows that, on average, surface cold tongue water moves northward toward the frontal region and dives below tilted front, whereas subsurface water north of the front moves southward toward the front, upwells, and then moves northward in the surface mixed layer. The model is used to demonstrate that this mean quasi-adiabatic secondary circulation is not a frozen field that migrates with the front but is instead highly dependent on the phase of the TIWs: southward-upwelling flow on the warm side of the front tends to occur when the front is displaced southward, whereas northward-downwelling flow on the cold side of the front occurs when the front is displaced northward. Consequently, when averaged in geographic coordinates, the observed and simulated TCs appear to be equatorially asymmetric and show little trace of a secondary circulation near the mean front.