Impacts of XBT,TAO,Altimetry and ARGO Observations on the Tropical Pacific Ocean Data Assimilation

This study aims at assessing the relative impacts of four major components of the tropical Pacific Ocean observing system on assimilation of temperature and salinity fields. Observations were collected over a period between January 2001 through June 2003 including temperature data from the expendable bathythermographs （XBT）, thermistor data from the Tropical Ocean Global Atmosphere Tropical Atmosphere-Ocean （TOGA-TAO） mooring array, sea level anomalies from the Topex/Poseidon and Jason-1 altimetry （T/P-J）, and temperature and salinity profiles from the Array for Real-time Geostrophic Oceanography （ARGO） floats. An efficient three-dimensional variational analysis-based method was introduced to assimilate the above data into the tropical-Pacific circulation model. To evaluate the impact of the individual component of the observing system, four observation system experiments were carried out. The experiment that assimilated all four components of the observing system was taken as the reference. The other three experiments were implemented by withholding one of the four components. Results show that the spatial distribution of the data influences its relative contribution. XBT observations produce the most distinguished effects on temperature analyses in the off-equatorial region due to the large amount of measurements and high quality. Similarly, the impact of TAO is dominant in the equatorial region due to the focus of the spatial distribution. The Topex/Poseidon-Jason-1 can be highly complementary where the XBT and TAO observations are sparse. The contribution of XBT or TAO on the assimilated salinity is made by the model dynamics because no salinity observations from them are assimilated. Therefore, T/P-J, as a main source for providing salinity data, has been shown to have greater impacts than either XBT or TAO on the salinity analysis. Although ARGO includes the subsurface observations, the relatively smaller number of observation makes it have the smallest contribution to the assimilation system.

The Application of ARGO Data to the Global Ocean Data Assimilation Operational System of NCC

In this paper, we have preliminarily studied the application of ARGO (Arrayfor Real-time Geostrophic Oceanography) data to the Global Ocean Data Assimilation System ofNational Climate Center of China (NCC-GODAS), which mainly contains 4 sub-systems such as datapreprocessing, real-time wind stress calculating, variational analysis and interpolating, and oceandynamic model. For the sake of using ARGO data, the relevant adjustment and improvement have beenmade at the corresponding aspects in the subsystems. Using the observation data from 1981 to 2003including the ARGO data of 2001 to July. 2003, we have performed a series of numerical experimentson this system. Comparing with the corresponding results of NCEP, It is illustrated that using ARGOdata can improve the results of NCC-GODAS in the region of the Middle Pacific, for instance SST,SSTA (SST anomalies), Nino index, sea sub-surface temperature, etc. Furthermore, it is obtained thatNCC-GODAS benefits from ARGO data in the other regions such as Atlantic Ocean, Indian Ocean, andextratropical Pacific Ocean much more than in the tropical Pacific.