Journal of Tropical Oceanography >
The interannual variation of summer upwelling in Zhoushan Islands and its relationship with ENSO
Copy editor: SUN Cuici
Received date: 2023-03-03
Revised date: 2023-03-30
Online published: 2023-06-20
Based on the sea surface temperature and wind data from 1968 to 2021, this paper analyzes the interannual variation of upwelling intensity in Zhoushan in summer, and the impact of El Niño-Southern Oscillation (ENSO) on upwelling. The temperature and wind upwelling indices both show that the upwelling in Zhoushan sea decreased in summer during 1982—2021, with the decreasing rates of 0.062℃·10a-1and 0.35 m3·s-1·(100m·a)-1, respectively. Recently, the weakened coastal wind stress causes the temperature upwelling index to decrease. According to the results, the wind upwelling index during La Niña events is larger than that during El Niño events and climatology. Further analysis of the relationship between ENSO and the wind upwelling index shows that ENSO affects the intensity of upwelling mainly by influencing the wind. In El Niño events, the southeast wind dominated Zhoushan sea weakens, leading to a decreasing upwelling intensity. While in La Niña events, the enhanced south wind benefits the development of upwelling.
Key words: Zhoushan; upwelling; interannual variation; ENSO; wind
QUAN Mengyuan , WANG Hui , LI Wenshan , WANG Aimei , LUO Jingxin . The interannual variation of summer upwelling in Zhoushan Islands and its relationship with ENSO[J]. Journal of Tropical Oceanography, 2024 , 43(1) : 48 -55 . DOI: 10.11978/2023026
图1 1982—2021年舟山海域夏季(6—8月)气候态月平均海表温度(SST, ℃)和风场(箭头, 单位: m·s-1)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(2020)4619号的标准地图制作。图中黑色方框A表示舟山上升流区, 黑色方框B表示不受上升流影响的背景海域 Fig. 1 The summer (June—August) monthly climatological average sea surface temperature (SST, ℃) and wind (unit: m·s-1) from 1982 to 2021. The black box A in the figure is the studied nearshore upwelling region, and the black box B is the background region |
表1 基于PDO不同位相下的El Niño年和La Niña年Tab. 1 El Niño years and La Niña years classified based on the different PDO phases |
El Niño年 | La Niña年 | |
---|---|---|
PDO正位相 | 1977, 1986, 1987, 1997, 2004, 2014, 2015, 2018 | 1983, 1984, 1988, 1955, 2005, 2016, 2017 |
PDO负位相 | 1968, 1969, 1972, 1976, 1982, 1991, 1994, 2002, 2006, 2009 | 1970, 1971, 1973, 1974, 1975, 1998, 1999, 2000, 2007, 2010, 2011, 2020, 2021 |
图2 1982—2021年夏季研究海域的海表温度及基于温度的舟山上升流指数的年际变化a.外海背景场海表温度; b.上升流区海表温度; c.上升流指数, 即近岸海表温度与离岸海表温度的差; 图中红色虚线为线性变化趋势 Fig. 2 Variations of averaged sea surface temperature (SST) and upwelling index in the study areas in summer of 1982—2021. (a) averaged SST in offshore background area; (b) averaged SST in nearshore upwelling area; (c) upwelling index is the difference between nearshore sea surface temperature and offshore sea surface temperature. Red dash lines show linear trends of the variation |
图4 基于风的上升流指数(WUI)与海洋Niño指数(ONI)的年际变化(相关系数为-0.36)Fig. 4 The interannual variation of wind-based upwelling index (WUI) and Ocean Niño Index (ONI), the correlation coefficient of the two is -0.36 |
图5 El Niño年(绿色)、La Niña年(红色)和常年(蓝色)风上升流指数的变化顶部橘色加号为PDO正位相, 底部蓝色圆圈为PDO负位相 Fig. 5 The variation of wind-based upwelling index during El Niño years (green), La Niña years (red) and natural years (blue). The top orange “+” represents the positive phase of PDO, while the bottom blue “o” represents the negative phase of PDO |
表2 不同等级的风上升流指数[单位: m3·s-1·(100m)-1]Tab. 2 Wind-based upwelling index of different levels [unit: m3·s-1·(100m)-1] |
等级 | 风上升流指数的取值范围 |
---|---|
1 | [−125,−75) |
2 | [−75,−37.5) |
3 | [−37.5,0) |
4 | [0,37.5) |
5 | [37.5,75] |
图6 (a) La Niña年和 (b) El Niño年夏季舟山海域风场距平分布(相对于1986—2021年的平均风场), (c)为La Niña年减去El Niño年的风场异常分布图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(2020)4619号的标准地图制作 Fig. 6 Wind anomalies in the Zhoushan sea in summer in (a) La Niña years and (b) El Niño years (relative to 1968—2021 average), (c) the difference between La Niña year and El Niño year |
图7 PDO正位相(a) La Niña年和(b) El Niño年夏季舟山海域平均风场异常; PDO负位相(c) La Niña年和(d) El Niño年夏季舟山海域平均风场异常(相对于1968—2021年的平均风场, 单位: m·s-1)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(2020)4619号的标准地图制作 Fig. 7 Composites of summer mean wind anomalies in the Zhoushan sea for (a) La Niña years and (b) El Niño years during the PDO positive phases, (c, d) during the negative PDO phases, respectively (relative to 1968—2021, unit: m·s-1) |
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