Journal of Tropical Oceanography >
Spatial and seasonal differences of the upper-ocean submesoscale processes in the South China Sea
Copy editor: YIN Bo
Received date: 2020-09-30
Request revised date: 2021-03-05
Online published: 2021-03-15
Supported by
National Key Research and Development Program of China(2017YFA0604104)
Opening Foundation of State Key Laboratory of Tropical Oceanography(South China Sea Institute of Oceanology)(LTO1907)
Chinese Postdoctoral Foundation(2018M642148)
Jiangsu Planned Projects for Postdoctoral Research Funds(2018K149C)
National Natural Science Foundation of China(41776040)
Laboratory for Ocean Dynamics and Climate, Pilot Qingdao National Laboratory for Marine Science and Technology(OCFL-201804)
Copyright
The South China Sea (SCS) is the largest marginal sea in the western Pacific Ocean. Due to the significant monsoons and the impact of the Kuroshio intrusion via the Luzon Strait, the local dynamic environment is complicated. Thus, the submesoscale behaviors in the SCS show clear spatial and temporal differences. In this paper, based on the outputs of a high-resolution numerical model, we examine the spatial and seasonal differences of submesoscale processes, influence depth and possible influencing factors in different sub-regions (the northern SCS, the central SCS basin, the western SCS, and the southern SCS). We find that the seasonal variation and mechanisms in each region is unique: The northern part is affected by the winter monsoon and the intrusion of the Kuroshio obviously, so that the mixed layer instability (MSI) is strong; and the submesoscale processes (SMPs) are active in winter. The SMPs in the central basin also shows stronger in winter and weaker in summer. The enhanced summer SMPs in the western SCS are attributed to the summer monsoon. The multi-island topography in the southern SCS generates great submesoscale wake eddies, which do not show significant seasonality.Statistical analysis shows that submesoscale processes tend to be associated with strong positive relative vorticity and high strain; in contrast, negative values of potential vorticity are more likelyto appear in the surface layer with poor fluid stability. Furthermore, we discuss the main energy sources and control factors of SMPs by analyzing their energetics.
Key words: South China Sea; submesoscale; seasonal variation; upper ocean; spatial difference
YANG Xiaoxiao , CAO Haijin , JING Zhiyou . Spatial and seasonal differences of the upper-ocean submesoscale processes in the South China Sea[J]. Journal of Tropical Oceanography, 2021 , 40(5) : 10 -24 . DOI: 10.11978/2020116
图1 水平分辨率为7.5km的最大模拟区域的水深分布情况(a)和水平分辨率1.5km的模拟子区域(b)图a中的方框为图b区域。图b中的方框表示不同的研究区域; 红色虚线表示南海诸岛归属范围线; 黑色虚线表示200m等深线。R1表示北部研究海域; R2表示中部研究海域; R3表示西部研究海域; R4表示南部研究海域。该图基于国家测绘地理信息局标准地图服务网站下载的审图号为GS(2016)1665的标准地图制作 Fig. 1 Water depth in the largest model domain with a horizontal resolution of 7.5 km (a), and in the sub-region with a horizontal resolution of 1.5 km (b) |
图2 研究区域10m层水平相对涡度ζ/f, 水平散度δ/f, 水平应变率S/f在1月15日(a~c)和7月15日(d~f)水平分布的瞬时图像图中黑色方框表示不同的研究区域; 红色虚线表示南海诸岛归属范围线; 黑色虚线表示200m等深线。审图号为GS(2016)1665 Fig. 2 Horizontal distributions ofζ/f, δ/f, and S/f in the 10 m layer of the model. An instantaneous image taken on January 15 (a~c), and on July 15 (d~f) |
图3 R1 (a, e, i)、R2 (b, f, j)、R3 (c, g, k)和R4 (d, h, l)各区域内平均水平相对涡度ζ/f均方根(a~d), 水平散度δ/f均方根(e~h), 水平应变率S/f (i~l)随时间、深度变化情况图中黑线表示该区域平均混合层深度随时间变化情况 Fig. 3 The variations of averaged ζ/f, δ/f, and S/f over time and depth in different regions. The black curve shows the variation of the averaged mixed-layer depth over time |
表1 不同区域特征参数上层50m各季节平均的结果Tab. 1 Seasonal averages of characteristic parameters of different regions in the upper 50 m |
次中尺度特征参量 | 区域 | 冬季(12—2月) | 春季(3—5月) | 夏季(6—8月) | 秋季(9—11月) |
---|---|---|---|---|---|
ζ/f的均方根值在不同 季节内的平均值 | R1 | 0.51 | 0.32 | 0.21 | 0.32 |
R2 | 0.41 | 0.37 | 0.30 | 0.30 | |
R3 | 0.38 | 0.33 | 0.47 | 0.51 | |
R4 | 0.70 | 0.73 | 0.70 | 0.72 | |
δ/f的均方根值在不同 季节内的平均值 | R1 | 0.19 | 0.11 | 0.07 | 0.12 |
R2 | 0.13 | 0.08 | 0.07 | 0.07 | |
R3 | 0.15 | 0.09 | 0.18 | 0.14 | |
R4 | 0.31 | 0.26 | 0.26 | 0.24 | |
S/f在不同季节内的 平均值 | R1 | 0.42 | 0.27 | 0.19 | 0.27 |
R2 | 0.34 | 0.32 | 0.25 | 0.25 | |
R3 | 0.32 | 0.29 | 0.37 | 0.38 | |
R4 | 0.58 | 0.58 | 0.57 | 0.55 |
图4 R1 (a, e, i)、R2 (b, f, j)、R3 (c, g, k)和R4 (d, h, l)各区域1月和7月份水平相对涡度ζ/f (a~d), 水平散度δ/f (e~h), 水平应变率S/f (i~l)的概率密度分布曲线相对涡度图像中的数字为不同月份的PDF的偏态系数 Fig. 4 PDF curves of ζ/f, δ/f, and S/f in January and July. The numbers in the relative vorticity images are the skewness coefficients of PDF in different months |
图7 1月15日(a~c)和7月15日(d~f)位涡q (a, d)及其分量qvert (b, e)、qbc (c, f)在表层10m深度的水平分布情况图中黑色实线S1、S2、S3为所选典型断面, 图中红色虚线表示南海诸岛归属范围线。审图号为GS(2016)1665 Fig. 7 Horizontal distributions of q and its components in different seasons at 10 m. The time in (a~c) and (d~f) is consistent with that in |
图8 典型断面S1 (a~c)、S2 (d~f)、S3 (h~j)处位涡q (a, d, h)及其分量qvert (b, e, i)、qbc (c, f, j)的分布情况图中黑色虚线为该断面混合层深度, 黑色实线为等密度线; 图h~j中的灰色部分表示地形 Fig. 8 Distributions of q and its components at S1, S2, and S3. The dashed line shows the mixed-layer depth at each section, and the solid contours are isopyrdensity lines |
图9 R1 (a, e)、R2 (b, f)、R3 (c, g)和R4 (d, h)各区域平均的斜压转换项PKE (a~d)、正压转换项BSK (e~h)随时间变化情况图中黑线为区域平均混合层深度随时间变化情况 Fig. 9 Variations of averaged PKE and BSK in each region over time. Panels from top to bottom correspond to regions R1~R4, respectively. The black curve shows the variation of regionally averaged mixed-layer depth over time |
图10 R1 (a, e)、R2 (b, f)、R3 (c, g)和R4 (d, h)各区域正压转换项BSK的水平分量HRS (a~d)与垂向分量VRS (e~h)随时间变化情况图中黑色实线表示混合层深度随时间变化情况 Fig. 10 Variations of HRS and VRS in different regions over time. Panels from top to bottom correspond to regions R1~R4, respectively. The black curve shows the variation of regionally averaged mixed-layer depth over time |
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