PHD DEFENSE: « Interannual and intraseasonal variability of the South Vietnam upwelling: the role of high-frequency atmospheric forcing, offshore and coastal ocean dynamics, and intrinsic oceanic variability »

– Duy Thai – Soutenance de thèse – LEGOS, Toulouse, France – 

Jury

Alexei Sentchev, LOG, Wimereux

François Colas, LOCEAN, Paris

Vo Luong Hong Phuoc, Univ. of Science, Ho Chi Minh city 

Rosemary Morrow, LEGOS, Toulouse

Bui Long Long, VNIO, Nha Trang (Vietnam )

Marine Hermann, LEGOS, Toulouse

Claude Estournel, LEGOS, Toulouse

Abstract

The South Vietnam Upwelling (SVU) develops off the Vietnamese coast (South China Sea, SCS) under the influence of southwest summer monsoon winds. A high resolution configuration (1 km at the coast) of the SYMPHONIE model was developed to study the functioning, variability and influence of the SVU. A simulation was first performed over the period 2009-2018. The realism of the simulation in terms of representation of ocean dynamics and water masses, from daily to interannual, and coastal to regional scales, was assessed in detail by comparison with available satellite data and four sets of in-situ observations. The interannual variability of the SVU is examined over its main areas of development: the southern (BoxSC) and northern (BoxNC) coasts, and the offshore area (BoxOF). For BoxSC and BoxOF, our results confirm the driving role of the summer regional mean wind and induced circulation. They moreover reveal that the spatial and temporal organization of mesoscale ocean structures and high frequency atmospheric forcing modulate this interannual variability. For BoxNC, the upwelling interannual variability is mainly determined by coastal circulation and mesoscale structures: similar summer wind conditions can be associated with very contrasting upwelling intensities, and vice versa, depending on the circulation in the BoxNC area. We then perform an ensemble of 10 twin simulations with perturbed initial conditions to examine the mechanisms involved in the daily to intraseasonal variability of upwelling. This ensemble reveals the role of the daily to intraseasonal chronology of wind forcing, but also the strong influence of Ocean Intrinsic Variability (OIV), related to the influence of coastal and mesoscale circulation. 

Zoom : https://cnrs.zoom.us/j/93077579427?pwd=YnY0eG5rYVlJQUlsbkZ4djFUcHhXQT09

ID de réunion : 930 7757 9427

Code secret : 73DGUN