Analysis of the northern South China Sea counter-wind current in winter using a data assimilation model
Analysis of the northern South China Sea counter-wind current in winter using a data assimilation model
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DOI：
10.1007/s10236-015-0817-y
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发表时间：
2015-02
期刊：
影响因子：
2.3
通讯作者：
Jiping Xie;Jiang Zhu;Laurent Bertino;F. Counillon
中科院分区：
文献类型：
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作者：
Jiping Xie;Jiang Zhu;Laurent Bertino;F. Counillon
近十年来，南海暖流由于其冬季在东南沿海逆风流动的特点而引起了人们的广泛关注。对SCSWC的观测监测还不足以对该洋流的特性进行可靠的评估。先前的建模尝试是在理想化或简化的框架下进行的，例如，粗分辨率、不切实际的风强迫、人工测深和/或缺少动力过程。目前尚不清楚上述近似会在多大程度上影响SCSWC的性能。本文综合了1993 - 2005年南海的最新资料同化系统。该系统采用带潮汐强迫的混合海洋模式（HYCOM），并受真实大气强迫的强迫。为了更真实地定位中尺度特征，系统利用集成最优插值（EnOI）同化沿航迹高程数据，研究1996-2005年SCSWC的特征。研究了冬季SCSWC的特征，发现冬季SCSWC主要沿100 m等深线流动，并以斜压结构存在于地表以下至50 m深度；主岩心位于20-30 m深度，由比陆架水温暖的水组成；而洋流的宽度小于100公里。同时，根据日输出，表明1月份的电流是高暂态的。另外，在没有潮汐强迫和同化的情况下进行的模拟表明，海流的瞬态特性主要是由大气强迫驱动的，而中尺度涡旋增强了海流的变率。相反，潮汐强迫似乎降低了南海swc的强度，正如潮流的潮汐整流所预期的那样。
The South China Sea Warm Current (SCSWC) has drawn considerable attentions in the past decade due to its characteristic of flowing against the wind direction along the coast of Southeast China during winter. Observational monitoring of the SCSWC is yet insufficient to firmly assess of the property of this current. Prior modeling attempts have been carried out in idealized or simplified framework, e.g., coarse resolution, unrealistic wind forcing, artificial bathymetry, and/or missing dynamical processes. It is still unclear to what extent the above approximations may affect the properties of the SCSWC. In this study, a state-of-the-art data assimilation system of the South China Sea has been integrated from 1993 to 2005. The system uses the Hybrid Ocean Model (HYCOM) with tidal forcing and is forced with realistic atmospheric forcing. In order to ensure a more realistic positioning of the mesoscale features, the system assimilates along-track altimetry data with the Ensemble Optimal Interpolation (EnOI) to investigate the properties of the SCSWC for the period 1996–2005. The properties of the SCSWC in winter time are investigated and found: the current mainly follows the 100 m isobaths and exists from immediately below the surface to the depth of 50 m with a baroclinic structure; the main core is located at 20–30 m depths and is composed of water warmer than the shelf water; and the width of the current is less than 100 km. Meanwhile, based on the daily output, it was shown that the current is highly transient in January. Additional simulations without tidal forcing and without assimilation suggest that the transient property of the current is mainly driven by the atmospheric forcing while the mesoscale eddies enhance its variability. On the contrary, tidal forcing seems to reduce the strength of the SCSWC, as expected from tidal rectifying of the current.