Interannual variation of the South China Sea circulation during winter: intensified in the southern basin

Zu, Tingting; Xue, Huijie; Wang, Dongxiao; Geng, Bingxu; Liu, Qinyan; Chen, Ju; He, Yuehui

doi:10.1007/s00382-018-4230-3

Cited by 33 publications

(28 citation statements)

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“…Journal of Geophysical Research: Oceans et al (2005). It has a closed cyclonic eddy (pattern "O") in the mature phase of an El Niño event, but an unclosed cyclonic circulation (pattern "U") in winter of La Niña and normal years (Zu et al, 2019).…”

Section: 1029/2019jc015139mentioning

confidence: 99%

Periodic Mesoscale Eddies in the South China Sea

Chu

Chen

2020

JGR Oceans

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Although numerous mesoscale eddies are observed in the South China Sea (SCS), a comprehensive study that focuses on periodic eddies has not yet been reported. Periodic eddies are a type of eddies that occur nearly annually in fixed time frames with similar patterns and trajectories. On the basis of in situ and satellite observations, this paper reports a periodic anticyclonic eddy in the western SCS (the Western SCS Anticyclonic Eddy, WAE) and elucidates the underlying processes responsible for its generation and evolution. The WAE is a seasonal phenomenon modulated by the Asian monsoon and basin-scale circulation. Usually, the WAE generates around 112°E, 14°N in February-March, induced by the cyclonic gyre in the northern SCS associated with the winter monsoon. The WAE occupies the western SCS for 5 months and finally dissipates in July due to the reversal of the monsoon and thus the circulation transition. The WAE shows important interannual variations associated with large-scale climate variation, and the Niño-3.4 index could be a potential predictor for its interannual variation. Finally, we summarize 13 periodic eddies in the SCS, including those unreported by previous studies. The period eddies in the SCS exhibit an inverse "L" shape vortex train structure along the western boundary and around the 17°N section, with an anticyclonic "phase" in summer and a cyclonic "phase" in winter. This study provides new knowledge for periodic eddies in the SCS and will benefit targeted observations of periodic eddies.Plain Language Summary Some mesoscale eddies in the ocean are observed to occur nearly annually, we here call them periodic eddies. Due to high occurrence rates, those periodic eddies have profound impacts on local physics, fishery, biology, and air-sea interaction. This study first reports a periodic anticyclonic eddy in the western South China Sea from in situ and satellite observations. By eddy reoccurrence rate, we then summarized all periodic eddies in the SCS. These eddies form the mean state of the mesoscale eddy field in the SCS. This study provides new knowledge for periodic eddies in the SCS and it also carries implications for future studies of periodic eddies in other regions.

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Section: 1029/2019jc015139mentioning

confidence: 99%

Periodic Mesoscale Eddies in the South China Sea

Chu

Chen

2020

JGR Oceans

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“…This suggests that buoyancy effect on the winter SCS WBC is opposite to wind-Kuroshio effects. The opposing effect of buoyancy flux was also mentioned in Yang et al (2002) and Zu et al (2018), although they did not focus on buoyancy effect on the winter SCS WBC. The two dashed cyan contours in the third panel are the isopycnals 25.00 and 25.45 kg/m 3 in December (contour interval is 0.45 kg/m 3 ).…”

Section: 1029/2019jc015079mentioning

confidence: 99%

“…This study focuses on the SCS WBC in winter, which is mainly attributed to the monsoon and Kuroshio intrusion (Chen & Xue, 2014). Many studies have investigated its pattern and interannual variability (Fang et al, 2012;He & Sui, 2010;He & Wang, 2007;Li et al, 2018;Quan et al, 2016;Wang et al, 2013;Zhao & Zhu, 2016;Zu et al, 2018). Based on drifter observations, He and Wang (2007) found that the winter SCS WBC is supplied by two branches: westward current from the eastern boundary of the SCS basin and Kuroshio intrusion, and the maximum velocity of the WBC occurs along the western slope in the SCS (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Buoyancy Effect on the Winter South China Sea Western Boundary Current

et al. 2019

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The month‐to‐month variation of the winter South China Sea (SCS) western boundary current (WBC) along the western slope is examined using drifter observations, satellite altimetry data, and an ocean reanalysis. The most surprising phenomenon is that the WBC velocity at the sea surface reaches the maxima in November–December, which cannot be explained by wind forcing and Kuroshio intrusion alone. Analysis results demonstrate that buoyancy effect should be considered to explain the month‐to‐month variation besides wind‐Kuroshio effects. In winter, cold‐and‐salty advection by the WBC from the north decreases/reverses the zonal density gradient in the seasonal pycnocline induced by wind forcing and Kuroshio intrusion and therefore weakens wind‐Kuroshio‐induced WBC. Buoyancy effect on the winter SCS WBC is opposite to wind‐Kuroshio effects. In addition, buoyancy effect reaches the maximum in January, which is concurrent with wind‐Kuroshio effects. As a result of their competition, the zonal density gradient in the seasonal pycnocline is maximum in November–December, resulting in the maximum surface velocity along the western slope occurring in November‐December. This study demonstrates the importance of buoyancy forcing to the winter SCS WBC.

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“…There have been few applications of REMO and ROM to East Asia, where the ocean conditions, especially in the western North Pacific (WNP), function as sources of both heat and moisture and have substantial impacts on the local and surrounding atmospheric circulation systems (Zhang et al 2015b;Zu et al 2019). The East Asian summer monsoon (EASM) is one of the most typical and important components of the climate in this region and affects nearly one-third of the world's population (Xue et al 2015;Cai et al 2017;Fan et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Added value of the regionally coupled model ROM in the East Asian summer monsoon modeling

Zhu

Remedio²,

Sein

et al. 2020

Theor Appl Climatol

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The performance of the regional atmosphere-ocean coupled model ROM (REMO-OASIS-MPIOM) is compared with its atmospheric component REMO in simulating the East Asian summer monsoon (EASM) during the time period 1980-2012 with the following results being obtained. (1) The REMO model in the standalone configuration with the prescribed sea surface conditions produces stronger low-level westerlies associated with the South Asian summer monsoon, an eastward shift of the western Pacific subtropical high (WPSH) and a wetter lower troposphere, which jointly lead to moisture pathways characterized by stronger westerlies with convergence eastward to the western North Pacific (WNP). As a consequence, the simulated precipitation in REMO is stronger over the ocean and weaker over the East Asian continent than in the observational datasets.(2) Compared with the REMO results, lower sea surface temperatures (SSTs) feature the ROM simulation with enhanced air-sea exchanges from the intensified low-level winds over the subtropical WNP, generating an anomalous low-level anticyclone and hence improving simulations of the low-level westerlies and WPSH. With lower SSTs, ROM produces less evaporation over the ocean, inducing a drier lower troposphere. As a result, the precipitation simulated by ROM is improved over the East Asian continent but with dry biases over the WNP. (3) Both models perform fairly well for the upper level circulation. In general, compared with the standalone REMO model, ROM improves simulations of the circulation associated with the moisture transport in the lower-to mid-troposphere and reproduces the observed EASM characteristics, demonstrating the advantages of the regionally coupled model ROM in regions where air-sea interactions are highly relevant for the East Asian climate.

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Interannual variation of the South China Sea circulation during winter: intensified in the southern basin

Cited by 33 publications

References 50 publications

Periodic Mesoscale Eddies in the South China Sea

Periodic Mesoscale Eddies in the South China Sea

Buoyancy Effect on the Winter South China Sea Western Boundary Current

Added value of the regionally coupled model ROM in the East Asian summer monsoon modeling

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