“…The computational cost of running an ensemble of independent 4D‐Var cycles in the EDA makes it necessary to reduce the size of the ensemble and the spatial resolution (both in inner and outer loops) of its members so it can conveniently be run in the operational schedule. The sampling errors introduced in the estimation of B by the limited ensemble size, and methods to control them, have been extensively discussed for background‐error standard deviations (Berre et al , ; Raynaud et al , , , ; Bonavita et al , ; Pannekoucke et al , ) and for the background‐error correlation structures (Pannekoucke et al , , ; Varella et al , ). An aspect that has received less attention is the impact of the different, considerably smaller, resolution at which the EDA members are currently run with respect to the resolution of the target assimilation system whose error statistics they are used to simulate.…”