Four-dimensional problem of variational initialization of hydrophysical fields of the World Ocean

The problem of four-dimensional variational initialization of velocity, temperature, and salinity fields in the World Ocean is considered. The ocean dynamics equations are written in the generalized sigma-system of coordinates on a sphere with arbitrary positions of coordinate poles. The World Ocean model has the spatial resolution 2.5 degrees x 2 degrees x 33. The computational north pole is shifted onto the continent to the point (60 degrees E, 60.5 degrees N), the south pole coincides with the geographic one. The numerical experiments consist of two stages. At the first stage, we perform the calculations of the direct World Ocean circulation model for the period of 3000 years. On the ocean surface we specify the climatic atmospheric forcing constructed from the averaged CORE data from the period 1958-2004 with the discreteness of 6 hours. At the second stage, the problem is solved in the 'variational initialization-forecast' mode. The calculation interval equals 1 year, the solution obtained at the first stage is taken as the initial condition. After the initialization, the calculation of the direct model in the forecast mode is performed up to the end of the current month of the year. The mean monthly fields of temperature and salinity from the Argo buoys data for year 2008 are used as assimilated observation data. The results of the calculations show that observation data assimilation leads to a noticeable improvement of treatment characteristics. The model values approach the observations, and the solution adequately reflects the observed structure of natural fields.