Upwelling off the west coast of Hainan Island in summer: Its detection and mechanisms

Lü, Xingang; Qiao, Fangli; Wang, Guansuo; Xia, Changshui; Yuan, Yue

doi:10.1029/2007gl032440

Cited by 52 publications

(45 citation statements)

References 8 publications

(9 reference statements)

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“…In contrast, in summer, the winds reverse their directions and blow from the southwest, triggering offshore Ekman transport of surface water over the shelf [ Liu et al ., ; Gan et al ., ; Jing et al ., ; Wang et al ., ]. As a result, persistent surface cooling and thermal fronts were frequently observed from satellite Sea Surface Temperature (SST) during the summer upwelling seasons, particularly on the western shelf of the NSCS [e.g., Hu et al ., ; Lü et al ., ; Su and Pohlmann , ; Jing et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Seasonal thermal fronts on the northern South China Sea shelf: Satellite measurements and three repeated field surveys

Jing

Fox‐Kemper

et al. 2016

JGR Oceans

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Seasonal thermal fronts associated with wind‐driven coastal downwelling/upwelling in the northern South China Sea are investigated using satellite measurements and three repeated fine‐resolution mapping surveys in winter, spring, and summer. The results show that vigorous thermal fronts develop over the broad shelf with variable widths and intensities in different seasons, which tend to be approximately aligned with the 20–100 m isobaths. Driven by the prevailing winter/summer monsoon, the band‐shaped fronts were observed with a magnitude exceeding 0.1°C/km in the subsurface, and accompanied by energetic coastal downwelling/upwelling due to shoreward/offshore Ekman transport. The downward/upward tilting of seasonal thermoclines across the shelf exceeds 20 m, significantly contributing to the development of thermal fronts over the shelf. In addition, the diagnostic analysis of Potential Vorticity (PV) suggests that the summer frontal activities induced by the coastal upwelling are more stable to convection and symmetric instabilities in comparison to the winter fronts associated with downwelling‐favorable monsoon forcing. This is primarily due to their essential differences in the upper ocean stratification and horizontal buoyancy gradients arising from wind forcing. At the same time, the coastal currents are substantially regulated by the seasonal winds. An expected lag correlation between the velocity from mooring measurements and alongshore wind stress is detected near the frontal region. These results indicate that seasonal wind forcing plays an important role in the frontal activities and coastal water transport over the shelf.

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Section: Introductionmentioning

confidence: 99%

Seasonal thermal fronts on the northern South China Sea shelf: Satellite measurements and three repeated field surveys

Jing

Fox‐Kemper

et al. 2016

JGR Oceans

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“…Detected from satellite images, persistent surface cooling and thermal fronts stretch several hundreds of kilometers along the East Coast and West Coast of Hainan Island, accompanied by high chlorophyll concentrations [Wang et al, 2001;Hu et al, 2003;L€ u et al, 2008]. However, as one of the most important physical processes in the NWSCS, the upwelling and upwelling-induced thermal fronts (hereinafter abbreviated as upwelling and thermal fronts) have not been well understood so far.…”

Section: Introductionmentioning

confidence: 99%

“…As a result, from spring to summer, the sea surface temperature (SST) along the coast of the NSCS does not monotonically increase with solar radiation but dramatically declines after the onset of the southwesterly monsoon, and results in a persistent surface cooling throughout the summer upwelling season, particularly over the continental shelf of northwestern SCS (NWSCS) [Hu et al, 2003;L€ u et al, 2008;Su and Pohlmann, 2009;Jing et al, 2011].…”

Section: Introductionmentioning

confidence: 99%

Summer upwelling and thermal fronts in the northwestern South China Sea: Observational analysis of two mesoscale mapping surveys

Jing

et al. 2015

JGR Oceans

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Persistent coastal upwelling and upwelling-induced thermal fronts in the northwestern South China Sea are investigated using satellite measurements, two intensive mesoscale mapping surveys and three bottom-mounted ADCPs. The results indicate that pronounced surface cooling and upwelling-related fronts with a width of 20-50 km occur around Hainan Island and persist through the summer upwelling season. Driven by the prevailing southwesterly monsoon, the subsurface cooling band is $6 C colder than the water offshore of the East Coast, where the thermal gradients are generally more than 0.1 C/km. The cold and nutrient-rich coastal water is identified to be derived primarily from the deep water of the outer shelf. At the same time, the spatial structure of the upwelling and thermal front, as well as the upwelling-related coastal currents, is significantly regulated by wind forcing. A prominent lagged correlation between the moored temperature records and alongshore wind stress is detected in the East Coast. The correlation coefficient is 20.8 with the temperature lagging behind wind stress by 2.2 days, indicating that the cooling band off the East Coast is dominated mostly by the alongshore southwesterly monsoon during the upwelling season.

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“…However, the water volume transported to the shelf induced by upwelling events has not been estimated. Recently, there have been some studies on upwelling around Hainan Island (Lü et al 2008;Su and Pohlmann 2009). Nevertheless, the dynamics of the upwelling, such as upwelling structure, the influence of wind events, and response of estuarine water, is not yet fully understood.…”

Section: Introductionmentioning

confidence: 99%

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

Su¹,

Wang

Pohlmann³

et al. 2011

Ocean Dynamics

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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.

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Upwelling off the west coast of Hainan Island in summer: Its detection and mechanisms

Cited by 52 publications

References 8 publications

Seasonal thermal fronts on the northern South China Sea shelf: Satellite measurements and three repeated field surveys

Seasonal thermal fronts on the northern South China Sea shelf: Satellite measurements and three repeated field surveys

Summer upwelling and thermal fronts in the northwestern South China Sea: Observational analysis of two mesoscale mapping surveys

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

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