Perspectives of the counter-wind current in the northern South China Sea in winter by assimilative modelling

Jiping Xie (Nansen Environmental and Remote Sensing Center, Norway)

CoAuthors

Jiang Zhu (Institute of Atmospheric Physics, Chinese Academy of Sciences, China); Laurent Bertino (Mohn Sverdrup Center, Nansen Environmental and Remote Sensing Center, Norway); Francois Counillon (Mohn Sverdrup Center, Nansen Environmental and Remote Sensing Center, Norway)

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Science Results from Satellite Altimetry: Finer scale ocean processes (mesoscale and coastal)

Presentation type: Type Poster

Off the coastline of south of China in winter, there are three adjacent current bands: the downwind Guangdong coast current, the South China Sea Warm Current (SCSWC) and the southwestward slope current related with the branch of Kuroshio in the SCS. Because of the counter-wind property of the SCSWC in winter, the related studies draw rather attention in past decades. However, the direct description of the structure and the width of this counter-wind current are very few and unconvincing due to lack of continuous current observations. On the other hand, the concerned simulations by ocean circulation model are limited by coarse resolution, unrealistic wind forcing, artificial bathymetry and incomplete dynamic process in previous studies. The structure features of SCSWC are still inconsistent or unclearly. In this study, a high-resolution Hybrid Ocean Model (HYCOM) with tidal forcing is driven by realistic reanalysis wind forcing in the SCS. And an effective data assimilation scheme of Ensemble Optimal Interpolation (EnOI) by Xie et al.(2011) is applied to assimilate along-track altimetry data into the model from 1993 to 2005. Based on the assimilative simulations on monthly and on daily, the newly features of the SCSWC structure can be obtained. The counter-wind current mostly is around 100m isobath alongshore, and its width is varied between 55 km and 85 km from west to east. The current cores no more than 10 cms-1 lie around 30-50m depth northeastward, and the velocities become loose in the across section from west to east gradually. The visible counter-wind current just emerges in part days of January of 2004 and 2005. Its transient property firstly suggests the SCSWC in winter should be treated a mesoscale phenomena in ocean circulation, and has a close relation with the synoptic process in atmosphere. Also the analysis of the Eddy Kinetic Energy (EKE) and the Mean Kinetic Energy (MKE) further verifies such kind of relationship between this current and the mesoscale eddy processes at the SCS in winter. It indicates the SCSWC is not so continuous and steady like the despripitons in previous studies that it is necessary to recognition on the view of mesoscale with high resolution.

Keywords: South China Sea Warm Current; Hybrid Coordinate Ocean Model; Data assimilation; Along-track altimetry data; Eddy Kinetic Energy;
 
Jiping Xie
Nansen Environmental and Remote Sensing Center
Norway
jiping.xie@nersc.no