3D-Var used in operational forecasting centers
Distance to forecast
Distance to observations
It is the same as the scalar formula for T, but now x is a
model state vector, with 106-8d.o.f., and yo is the set of
observations, with 105-9 d.o.f.
R is the observational error covariance,
B the forecast error covariance.
In 3D-Var B is constant: it does not include “errors of the