Distance-Dependent Filtering in a 4DVar Based on Historical Forecast Ensemble
基于历史预报的四维变分资料同化（4DVar）方法中的滤波

An economical approach to implement the variational data assimilation(4Dvar) using the technique of Historical Sample Projection(HSP) is proposed,it is based on dimension reduction using an ensemble of historical samples to define a subspace,directly obtains an optimal solution in the reduced space and does not require implementation of the adjoint of tangent linear approximation.But the ensemble is composed of far fewer members than both the number of observational data and the degrees of freedom of the mo...