Variational Data Assimilation for the Global Ocean - Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications - page 307

a

b

Fig. 13.4 Cross sections of vertical correlation length scales and density from Pacific basin run of
global HYCOM. ( a ) Vertical length scales (m); ( b ) Density (kg m 3 ) =

;

also include auto- and cross-correlations of the u v vector velocity components.

However, at the present time, there are no operational sources of ocean current
observations available for the assimilation, although the capability to assimilate
velocity data is built into the 3DVAR system. A full derivation of the multivariate
horizontal correlations is provided in Daley ( 1991 ). The multivariate correlations
are derived from the first and second derivatives of the SOAR (or Gaussian) model
function and require precise calculation of the angles between any two locations in
order to guarantee a symmetric correlation matrix.

13.3.4 Background Error Variances

Background error variances are poorly known in the ocean and are likely to be
strongly dependent on model resolution and other factors, such as atmospheric