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The CSS projects

China Seas

P4 - Ocean Data Assimilation and Nowcasting System for the China Marginal Seas

Configuration
At the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, a project supported by the Natural Science Foundation of China is underway to develop a coastal ocean nesting modeling/assimilation system that focuse on potential operational coastal ocean forecast for Chinese Waters.

Currently there are two candidate modeling/assimilation systems are under developing. One is based on an IAP eta-coordinate, 3-D, baroclinic regional ocean model. The model can be multi-nested at various resolutions. Accompanying data assimilation system (OVALS) is based on 3DVAR (Yan et al., 2004; Zhou et al., 2004; You et al., 2003; and Zhu et al., 2006).
Currently, a 1/4 degree version is running the OVALS assimilation and a 1/12 degree version is running in the simulation mode. Another candidate uses HYCOM as the model and an ensemble Kalman filter as data assimilation scheme. The two systems are going to use GODAE products to provide open boundary conditions. Currently a large domain model is used to provide open boundary conditions. The target processes mainly focus on the variations of the shelf fronts in the East China Sea (ECS) and the Yellow Sea (YS), and upwelling along Chinese coast in the time scales from few hours to several days. The mesoscale eddies in the South China Sea (SCS) are also studied.

Other important processes such as Korushio intrusions into ECS, YS and the SCS and mesoscale eddies in ECS and YS that maybe harder to attack due to more complicated mechanisms and the lack of routine, high temporal-spatial resolution observations resolving these processes will be focused in future.

Another system we used is HYCOM that uses 2-step one-way nesting. The larger domain covers the Western-Pacific and the Indian Ocean at the resolution of about 1/4 degree. The smaller domain covers the Yellow Sea, the East China Sea and the South China Sea, with the resolution of 1/10 degree. The data assimilation system used is based on EnKF in which some static ensembles are "dressed" to few dynamical ensembles in order to reduce the computational cost.

Objectives of system
For the Chinese CSS modeling/assimilation system developed, the main objectives are providing temperature, salinity and velocity reanalysis fields based on high resolution, nested models and GHRSST, GTSPP, coastal station and altimeter observations. The main applications of the reanalysis products include processes studies and ecosystem modeling. The customers are mainly from the scientific community.

Use of GODAE solutions
The large-scale GODAE outputs are needed to provide open boundary conditions for the nested models of Chinese Waters. Currently we do not consider more sophisticated downscaling schemes. However there is a potential interest to implement such downscaling schemes using GODAE outputs. The temperature, salinity and velocity fields from GODAE products are planned to be used as open boundary conditions in the China coastal model system. The GODAE sea surface height (SSH) fields are also have the potential to constrain the SSH field of coastal models at the deep part of the coastal model domains near open boundaries. The tidal sea level boundary conditions from large scale GODAE estimates are also important to CSS models. For Chinese CSS, the Kuroshio plays an important role in the circulation patterns, thermal fronts, upwelling in the north of SCS and ECS. The Kuroshio also contributes to the Yellow Sea Warm Current. The tidal mixing is very important in the shelf fronts formation. Therefore the outputs from the GODAE large scale estimates are required to provide reliable Kuroshio axis/transport and tidal open boundary conditions.

 

Project status
A new project will start in 2007 with the objective to develop a nowcasting system for Chinese CSS.


References
C. X. Yan, J. Zhu and G. Q. Zhou, 2004: The roles of vertical correlation of the background covariance and T-S relation in estimation temperature and salinity profiles from surface dynamic height. J. Geophys. Res. 109. doi:10.1029/2003JC002224

You X. B., G. Zhou, J. Zhu, R. Li and Q. Zeng, 2003: Sea Temperature Data Assimilation System for the China Sea and Adjacent Areas, Chinese Science Bulletin, 48 Supp. II. 70-76.

You X. B., Li R., Zhang M, Zeng Q., 2001: Numerical Calculation of the Wintertime Circulation in the South China Sea by using a Baroclinic Model, Acta Oceanologia Sinica, Vol. 23, No. 6, (In Chinese with English Abstact)

G. Zhou, W.Fu, and J. Zhu, 2004: The impact of location dependent correlation length scales of background covariance on an ocean data assimilation system. Geophy. Res. Letters, 31, L21306, doi: 10.1029/2004GL020579.

Zhu J., G.. Q. Zhou, C. X. Yan and X. B. You, 2006: A three-dimensional variational ocean data assimilation system: Scheme and preliminary results. Science in China (D), 49(11), 1212-1222, doi: 10.1007/s11430-006-1212-9..

(Last Updated: 17-01-2008)