Overview of the South China Sea circulation and its influence on the coastal physical oceanography outside the Pearl River Estuary

Pohlmann³

et al. 2011

Ocean Dynamics

The influence of meteorological variation, i.e., typhoon and precipitation events, on the coastal upwelling off the eastern Hainan Island was studied based on observations taken during two upwelling seasons. The observations were made in August 2007 and July 2008, respectively. We found that, in principle, similar structure of sea surface temperature and bottom temperature prevailed in both observational periods, providing evidence that upwelling events occur frequently during the summer monsoon along the eastern Hainan shelf. Based on a simple momentum balance theory, we studied the balances between momentum fluxes, wind stress, and bottom stress. The results showed that the Burger number is S ≈ 1, indicating that the crossshelf momentum flux divergence was balanced by the wind stress and the onshore return flow occurred in the interior of the water column. Hence, a conceptual model of the upwelling structure was built for further understanding of upwelling events. In addition, it was also observed that variations in the strength of upwelling are controlled by storm events, i.e., strong northerly winds change the structure of the thermocline on the shelf significantly. The strong mixing caused by wind reduces the strength of the thermocline, in particular in coastal seas. Based on our conceptual model, a frontal zone between mixed coastal water and offshore water develops which destabilizing the water column and hence decreases the upwelling strength. Freshwaters from the two main rivers in the Wenchang Bay are confined to the coastal area less than 20-30 m deep, as confirmed by our water mass analysis. Freshwater discharge stabilized the water column, inhibiting the upwelling as shown by the potential energy calculation. Consequently, estuarine water only inhibits the upwelling in the near coastal area. Therefore, it can be concluded that estuarine water does not have a significant impact on upwelling strength on the shelf.

Section: Introductionmentioning

confidence: 99%

The influence of meteorological variation on the upwelling system off eastern Hainan during summer 2007–2008

Su¹,

Pohlmann³

et al. 2011

Ocean Dynamics

“…While the clustering method groups these eddies into E1, Z1 and Z2 divide this area according to different generation mechanisms. Eddies generated in Z1 are probably caused by frontal instability at the Kuroshio intrusion Su, 2004). And Qu et al (2000) found intense positive wind stress curl would generate cyclonic eddies in eastern Z2.…”

Section: Four-cluster Resultsmentioning

confidence: 99%

A clustering analysis of eddies' spatial distribution in the South China Sea

et al. 2013

Ocean Sci.

Abstract. Spatial variation is important for studying the mesoscale eddies in the South China Sea (SCS). To investigate such spatial variations, this study made a clustering analysis on eddies' distribution using the K-means approach. Results showed that clustering tendency of anticyclonic eddies (AEs) and cyclonic eddies (CEs) were weak but not random, and the number of clusters were proved greater than four. Finer clustering results showed 10 regions where AEs densely populated and 6 regions for CEs in the SCS. Previous studies confirmed these partitions and possible generation mechanisms were related. Comparisons between AEs and CEs revealed that patterns of AE are relatively more aggregated than those of CE, and specific distinctions were summarized: (1) to the southwest of Luzon Island, AEs and CEs are generated spatially apart; AEs are likely located north of 14 • N and closer to shore, while CEs are to the south and further offshore. Overlaps of AEs and CEs in the northeastern and southern SCS were further examined considering seasonal variations. The northeastern overlap represented near-concentric distributions while the southern one was a mixed effect of seasonal variations, complex circulations and topography influences.

“…The eastern part of the SCS warm The along-isobath gradient of the density field interacts with the topography that supplies negative potential vorticity and drives the column-integrated flow away from the isobaths, veering toward the deep sea (Wang et al 2013a). In summer, under southwesterly monsoon forcing, a northeastward current, denoted as the western boundary current of the SCS, flows along the Vietnam coast, the south and east coasts of Hainan Island, and the northern SCS coast (Su 2004). Upwelling usually occurs along these coasts because of the wind and topographical effects (e.g., Xie et al 2007;Jing et al 2009;Su and Pohlmann 2009;Shu et al 2011a;).…”

Section: Sc I E Nti F Ic Applic Atio N Smentioning

confidence: 99%

“…In summer, under southwesterly monsoon forcing, a northeastward current, denoted as the western boundary current of the SCS, flows along the Vietnam coast, the south and east coasts of Hainan Island, and the northern SCS coast (Su 2004). Upwelling usually occurs along these coasts because of the wind and topographical effects (e.g., Xie et al 2007;Jing et al 2009;Su and Pohlmann 2009;Shu et al 2011a;). Cold-water spread related to upwelling can reduce the local wind speed and precipitation because of the increased static stability in the near-surface atmosphere, indicating the existence of an ocean-atmosphere feedback mechanism .…”

Section: Sc I E Nti F Ic Applic Atio N Smentioning

confidence: 99%

“…Driven by seasonal monsoonal winds, the upperlayer circulation over the deep basin of the SCS displays a basinwide cyclonic circulation in winter and a cyclonic northern gyre and anticyclonic southern gyre during summer Qu 2000;Su 2004;Fang et al 2002;Gan et al 2006;Dippner et al 2007;Gan and Qu 2008). Under the forcing of monsoon and complex topography, the SCS is characterized by high mesoscale eddy activity Lin et al 2007; F. Chen et al 2010;G.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Toward a Mesoscale Hydrological and Marine Meteorological Observation Network in the South China Sea

Yang

Bulletin of the American Meteorological Society

Huang

et al. 2015

Air–sea interaction in the South China Sea (SCS) has direct impacts on the weather and climate of its surrounding areas at various spatiotemporal scales. In situ observation plays a vital role in exploring the dynamic characteristics of the regional circulation and air–sea interaction. Remote sensing and regional modeling are expected to provide high-resolution data for studies of air–sea coupling; however, careful validation and calibration using in situ observations is necessary to ensure the quality of these data. Through a decade of effort, a marine observation network in the SCS has begun to be established, yielding a regional observatory for the air–sea synoptic system. Earlier observations in the SCS were scarce and narrowly focused. Since 2004, an annual series of scientific open cruises during late summer in the SCS has been organized by the South China Sea Institute of Oceanology (SCSIO), carefully designed based on the dynamic characteristics of the oceanic circulation and air–sea interaction in the SCS region. Since 2006, the cruise carried a radiometer and radiosondes on board, marking a new era of marine meteorological observation in the SCS. Fixed stations have been established for long-term and sustained records. Observations obtained through the network have been used to study regional ocean circulation and processes in the marine atmospheric boundary layer. In the future, a great number of multi-institutional, collaborative scientific cruises and observations at fixed stations will be carried out to establish a mesoscale hydrological and marine meteorological observation network in the SCS.