Preprints
https://doi.org/10.5194/os-2021-121
https://doi.org/10.5194/os-2021-121

  07 Jan 2022

07 Jan 2022

Review status: this preprint is currently under review for the journal OS.

Role of wind, mesoscale dynamics and coastal circulation in the interannual variability of South Vietnam Upwelling, South China Sea. Answers from a high resolution ocean model

Thai To Duy1,2,3, Marine Herrmann1,2, Claude Estournel1, Patrick Marsaleix1, Thomas Duhaut1, Long Bui Hong3, and Ngoc Trinh Bich2 Thai To Duy et al.
  • 1LEGOS, IRD, UMR5566, IRD/CNES/CNRS/Université de Toulouse, 31400 Toulouse, France
  • 2LOTUS Laboratory, University of Science and Technology of Hanoi (USTH), Vietnam Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam
  • 3Institute of Oceanography (IO), Vietnam Academy of Science and Technology (VAST), Nha Trang, Vietnam

Abstract. The South Vietnam Upwelling (SVU) develops in the South China Sea off the Vietnamese coast under the influence of southwest monsoon winds. A very high resolution configuration (1 km at the coast) of the SYMPHONIE model was developed over the western coastal region of the South China Sea. A simulation was performed over the period 2009–2018 to study the functioning, variability and influence of oceanic circulation and hydrology in the coastal region, in particular of the SVU. The realism of the simulation in terms of representation of ocean dynamics and water masses, from daily to interannual and coastal to regional scales, is assessed here in detail by comparison with available satellite data and 4 sets of in-situ observations. The interannual variability of the SVU is examined for its 4 main development areas: the southern (SCU) and northern (NCU) coasts, the offshore area (OFU), and the Sunda Shelf area off the Mekong Delta (MKU). For the SCU and OFU, our results confirm the driving role of the summer mean wind and the summer circulation over the offshore area in the interannual variability of the upwelling intensity. They moreover reveal the impact of the spatial and temporal organization of mesoscale ocean structures and high frequency atmospheric forcing. For the NCU, the upwelling interannual variability does not seem to be related to regional scale forcing and dynamics, but is mainly determined by coastal mesoscale structures and circulation: similar summer wind conditions can be associated with very contrasting NCU intensities, and vice versa, depending on the circulation in the NCU area. Finally, our study reveals that upwelling also develops off the Mekong Delta, with an interannual variability mostly determined by the summer wind and the wind-driven circulation over the SVU region.

Thai To Duy et al.

Status: open (until 04 Mar 2022)

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Thai To Duy et al.

Thai To Duy et al.

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Short summary
The summer South Vietnam Upwelling develops in the South China Sea, under the influence of monsoon winds. Cold, nutrient-rich waters rise to the surface, where photosynthesis occurs. This biologically active area is essential for the fishing activity. We have developed a very high resolution model to better understand the factors that drive the variability of this upwelling, along the coast and offshore: summer mean to daily chronology of wind, mesoscale ocean dynamics to coastal circulation.