Characterizing the sea-surface circulation in the gulf of tonkin by using numerical model and hf radar data

The Gulf of Tonkin, which locates in the north-west of South China Sea, is enclosed by North Vietnamese coast in the west, the Chinese coast to the north and Leizhou peninsula and Hainan island in the east. The gulf extends from 105o36’E to 109o55’E and from 17oN to 21o52’N. Tonkin gulf is quite shallow, the water depth ranges mostly from 40 – 70m and the deep water locates in the south of the gulf, which also is the main entry for water interactions between Tonkin gulf and the South China Sea. Although having numerous studies conducted by numerical model, the circulation in Tonkin gulf remains controversial due to the lack of observational data over the entire domain. In the previous LaMer collaboration project “Sea-surface current features in the Gulf of Tonkin observed from altimetry satellite and High-Frequency Radars” (June 2017), we have successfully applied the methods and technique of combining HF Radar data and satellite altimetry data in analyzing the surface circulation in Tonkin Gulf. The positive outcomes of the mini-project have revealed the inter-annual and seasonal variations of the surface current in this region (Figure 1). Although data collected from High-Frequency Radars and satellites are reliable with high resolution of both spatial and temporal, the characteristics of sea-surface current in the Tonkin Gulf are investigated and described for a relatively limited area. The reason for the limitation of the results is the lack of drifter buoys data and the spatial coverage of HF Radar in Tonkin Gulf (Figure 2). The study of the sea-surface current in the entire Gulf of Tonkin is necessary to not only characterize the seasurface circulation but also serve other environmental research. The purpose of this study is that we continue to investigate the ocean hydrodynamics of the Tonkin Gulf by taking advantage of the state-of-the-art numerical model by ROMS and the continuous monitoring of High Frequency radar system in Vietnam. Surface current in Summer Surface current in Winter