3D structure and seasonal variation of temperature fronts in the shelf sea west of Guangdong
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摘要: 基于2018–2019年现场高分辨率温度观测和1993–2021年的CMEMS再分析海表温度(SST)和风场数据,分析粤西陆架海温盐锋的三维结构、季节变化和影响机制。多年SST数据显示,海表温度锋冬季最强、出现概率和覆盖宽度最大,量值分别为0.049℃/km、75%和66 km。春季和夏季次之,而秋季则几乎完全消失。冬季锋面平均离岸50 km,夏季则向岸靠近为23.1 km。2018年春季、夏季和2019年夏季的现场观测进一步给出锋面在次表层的三维结构,结果显示春、夏季20 m等深线以浅处均有锋面存在,该锋面是沿岸高温海水与离岸低温海水辐聚而成,随着深度的增加锋面强度减小,覆盖范围向岸收缩。20 m以深水域锋面在次表层中强于表层,随深度增加而增强并向岸偏移。相关性和信息流分析发现,海表面风应力旋度和沿岸风是影响粤西陆架海表温度锋面的重要因素。该温度锋存在年际变化,PDO负位相时的La Niña年锋面强度出现极大值,而PDO正位相时的El Niño年则对应极小值。Abstract: Using reanalysis sea surface data and in-situ high-resolution observations in spring, summer 2018, and summer 2019, this study analyzes the 3D structure and seasonal variation of temperature fronts in the shelf sea west of Guangdong. The results show that the sea surface temperature (SST) fronts reach the strongest intensity up to 0.049°C/km in winter, with the largest occurrence probability of 75% and coverage of 66 km. The SST fronts weaken in spring and summer, and almost disappear in autumn. The average offshore distance of the front is 50 km in winter and 23.1 km in summer. The in-situ observations show a strong thermal front in coastal areas shallower than 20 m in both spring and summer. The front gets weaker and closer to the coast in deeper layers and is associated with warm coastal water and cold shelf water. In shelf areas deeper than 20 m, the fronts in the subsurface layer are stronger than in the surface layer and shift shoreward in deeper layers. The correlation coefficient and information flow between the surface wind and frontal parameters reveal that the surface wind stress curl and along-coast wind are the most important factors affecting the surface thermal front. These thermal fronts also have interannual variations, with maximum intensity in La Niña years with negative PDO and minimum intensity in El Niño years with positive PDO.
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Key words:
- ocean front /
- seasonal variation /
- 3D structure /
- information flow /
- shelf west of Guangdong
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图 3 锋面出现概率的季节分布
a. 冬天;b. 春天;c. 夏天;d. 秋天。灰色等值线为水深,蓝色箭头为海面10 m风矢量,洋红色实线为锋面中心线
Fig. 3 Seasonal distribution of mean occurrence probabilities of the front at the sea surface
a. Winter; b. spring; c. summer; d. autumn. Gray isolines represent the unter depth and blue arrows represent the wind vectors of 10 m on the sea surface. The solid magenta line is the centerline of the front
图 4 锋面指数I的季节分布
a. 冬天;b. 春天;c. 夏天;d. 秋天。灰色等值线为水深,蓝色箭头为海面10 m风矢量,洋红色实线为锋面中心线
Fig. 4 Seasonal distribution of front index I at the sea surface
a. Winter; b. spring; c. summer; d. autumn. Gray isolines represent the unter depth and blue arrows represent the surface wind vectors of 10 m on the sea surface. The solid magenta line is the centerline of the front
图 6 现场观测航次期间平均CMEMS再分析SST和ECWMF再分析风场分布
a. 2018年春季;b. 2018年夏季;c. 2019年夏季。黑色实心点为站位,白色箭头为海面风矢量
Fig. 6 Sea surface temperature (SST) from CMEMS reanalysis data and sea surface wind field from ECWMF reanalysis data during the cruise observations
a. Spring 2018; b. summer 2018; c. summer 2019. The black dots represent stations, and the white arrows represent the surface wind vectors
图 7 2018年春季(a, d, g)、2018年夏季(b, e, h)和2019年夏季(c, f, i)观测温度水平分布
a–c为2 m,d–f为8 m,g–i为12 m。蓝色实线和灰色实线分别为海岸线和等深线
Fig. 7 Horizontal distribution of temperature in spring 2018 (a, d, g) , summer 2018 (b, e, h), and summer 2019 (c, f, i)
a–c at 2 m, d–f at 8 m, and g–i at 12 m. The blue and gray solid lines represent the coastline and isobaths, respectively
图 8 2018年春季(a, d, g)、2018年夏季(b, e, h)和2019年夏季(c, f, i)观测温度水平梯度分布
a–c为2 m,d–f 为8 m,g–i为12 m。蓝色实线和灰色实线分别为海岸线和等深线
Fig. 8 Horizontal distribution of temperature gradient in spring 2018 (a, d, g) , summer 2018 (b, e, h), and summer 2019 (c, f, i)
a–c at 2 m, d–f at 8 m, and g–i at 12 m. The blue and gray solid lines represent the coastline and isobaths, respectively
图 12 1993–2021年ENSO事件发生期间的SST分布
a. 1997–1998年El Niño;b. 2009–2010年El Niño;c. 2015–2016年El Niño;d. 2018–2019年El Niño;e. 1999–2000年La Niña;f. 2007–2008年La Niña;g. 2010–2011年La Niña;h. 2020–2021年La Niña。白色箭头为表面流速,黑色箭头为海上10 m风矢量,黑色实心点位置为锋面位置
Fig. 12 Distribution of SST during the 1993–2021 ENSO events
a. 1997–1998 El Niño; b. 2009–2010 El Niño; c. 2015–2016 El Niño; d. 2018–2019 El Niño; e. 1999–2000 La Niña; f. 2007–2008 La Niña; g. 2010–2011 La Niña; h. 2020–2021 La Niña. White arrows are surface currents, black arrows are offshore 10 m wind vector and the black solid dot position is the frontal areas
表 1 锋面参量与风参量的相关系数
Tab. 1 Correlation coefficient between frontal parameters and wind parameters
沿岸风应力
总体(冬,夏)向岸风应力
总体(冬,夏)风应力旋度
总体(冬,夏)风应力散度
总体(冬,夏)沿岸流
总体(冬,夏)锋面强度 0.45*(0.54, 0.50) 0.25*(0.55, 0.15) 0.47*(0.57, 0.3) 0.37*(0.13, 0.52) 0.42* (0.66, 0.56) 出现概率 0.42*(0.67, 0.51) 0.1(0.29, 0.1) 0.32*(0.65, 0.43) 0.32*(0.15, 0.46) 0.25* (0.59, 0.56) 覆盖宽度 0.52*(0.55, 0.58) 0.35*(0.45, 0.03) 0.51*(0.54, 0.47) 0.32*(0.51, 0.53) 0.13(0.62, 0.51) 离岸距离 0.38*(0.60, 0.53) –0.55*(–0.5, 0.24) 0.2*(0.36, 0.42) 0.2*(0.33, 0.1) 0.1(0.26, 0.22) 注:*表示相关系数通过95%的置信度检验,括号内分别为冬季(斜体)和夏季的相关系数。 表 2 锋面参量和风参量的信息流计算结果
Tab. 2 Information flow calculation results between frontal parameters and wind parameters
锋面强度 出现概率 覆盖宽度 离岸距离 沿岸风 向岸风 风应力旋度 锋面强度 – – – – 0.1 0.03 0.28 出现概率 – – – – 0.12 –0.002 0.14 覆盖宽度 – – – – 0.1 0.05 0.23 离岸距离 – – – – 0.22 0.29 0.09 沿岸风 –0.045 –0.017 –0.02 –0.08 – – – 向岸风 –0.03 –0.002 –0.05 0.008 – – – 风应力旋度 –0.14 –0.1 –0.12 –0.11 – – – 注:表中“–”为相同变量之间的结果,无意义。 -
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