Mesoscale variability in the northeastern tropical Pacific: Forcing mechanisms and eddy properties
Mesoscale variability in the northeastern tropical Pacific: Forcing mechanisms and eddy properties
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DOI：
10.1029/2012jc008008
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发表时间：
2012-07
影响因子：
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通讯作者：
Jun‐Hong Liang;J. McWilliams;J. Kurian;F. Colas;Peng Wang;Y. Uchiyama
中科院分区：
文献类型：
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作者：
Jun‐Hong Liang;J. McWilliams;J. Kurian;F. Colas;Peng Wang;Y. Uchiyama
[1]利用一系列数值解和卫星观测资料，研究了热带太平洋东北部中尺度涡的产生机制和性质。Tehuantepec海湾和Papagayo海湾上空的山地风急流的空间和时间分辨率对于准确模拟区域中尺度变化至关重要。前人提出的三种涡旋产生机制是局地瞬变风强迫、低频风和边界强迫的组合以及远赤道开尔文波强迫。在我们的模式中，瞬变风场由具有天气变率的风场来表示，而遥远的赤道开尔文波则由具有年际变率的5天开放边界条件来表示。对比了有和没有高频强迫的解决方案，以评估这三种机制的贡献。低频风和边界强迫的综合作用是近地平流层的主要涡旋强迫机制。在Tehuantepec地区，高频风强迫对中尺度变率的贡献大于远赤道开尔文波强迫，而在Papagayo地区，两者的贡献相当。Tehuantepec和Papagayo地区的涡旋在幅度和大小上都更大，并且比NETP其他地区的涡旋更有可能偏向赤道。涡旋的最大温度异常出现在50m深度附近。生命周期为6周的涡旋更有可能是反气旋的，而生命周期为6周的涡旋更有可能是气旋性的。大幅度长寿命涡旋的反气旋优势是风驱动的非对称偶极子自旋和大幅度气旋演化脆弱性的综合结果。
[1] The generation mechanisms and properties of the mesoscale eddies in the northeastern tropical Pacific (NETP) are studied using a series of numerical solutions and satellite observations. The spatial and temporal resolution of mountain wind jets over the Gulfs of Tehuantepec and Papagayo are essential for an accurate modeling of the regional mesoscale variability. Three previously proposed eddy generation mechanisms are the local transient wind forcing, the combined low-frequency wind and boundary forcing, and the remote equatorial Kelvin wave forcing. In our model, the transient wind-forcing was represented by wind fields with synoptic variability, and the remote equatorial Kelvin wave forcing by 5-day open boundary conditions with interannual variability. Solutions with and without high-frequency forcings are contrasted to evaluate the contributions of the three mechanisms. The combined low-frequency wind and boundary forcing is the primary eddy forcing mechanism in the NETP. In the Tehuantepec region, the high-frequency wind-forcing contributes more to the mesoscale variability than the remote equatorial Kelvin wave forcing, while in the Papagayo region, their contributions are comparable. Eddies in the Tehuantepec and Papagayo regions are larger in both amplitude and size, and are more likely to deflect equatorward than eddies in the rest of the NETP. The maximum temperature anomaly of eddies is at around 50 m depth. Eddies with lifetimes >6 weeks are more likely anticyclonic, while eddies with lifetimes <6 weeks are more likely cyclonic. The anticyclone-dominance for large-amplitude long-lived eddies is the combined consequence of wind-driven asymmetric dipole spin-up and the evolutionary fragility of large-amplitude cyclones.