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

Abstract

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.

Water mass circulation and residence time using Eulerian approach in a large coastal lagoon (Nokoué Lagoon, Benin, West Africa)

“…In this study, we utilized wind forcing with a relatively coarse spatial resolution of ¼° (~25 km) from ECMWF, which was then interpolated onto our simulated domain. However, numerous studies have highlighted the significant impact of wind spatial resolution on surface dynamics in semi-enclosed basins or coastal oceans (Duy et al, 2022;Cerralbo et al, 2016). Given that wind plays a crucial role in influencing the circulation and residence times (TR) of the Nokoué Lagoon, future investigations should explore the sensitivity of lagoon dynamics to the spatial resolution of wind data.…”

River freshwater effects on the South-East Asian ocean dynamics

“…The numerical experiments analyzed in this study were realized running the SYMPHONIE model (Marsaleix et al, 2008), whose detailed description is provided by To Duy et al (2022). We use a regular 5 km resolution mesh grid over the whole SEA region, expanding from 90°E to 147°E and from 18°S to 24°N (Figure 1), and in the vertical 60 sigma layers.…”