Methods for Observation Data Assimilation in Problems of Physics of Atmosphere and Ocean

This paper presents a review and analysis of approaches to data assimilation in problems of geophysical hydrodynamics, from the simplest sequential assimilation schemes to modern variational methods. Special attention is paid to the study of the problem of variational assimilation in a weak formulation, in particular, to the construction of an optimality system and the estimation of the covariance matrices of the optimal solution errors. This is a new direction of research in which the author has obtained some results.