Fig. 4.

Root Mean Square difference to the CHAOS-2 model of three Ensemble Kalman Filter simulations. The thin green lines represent the evolution of 1000 individual field model ensemble states over 61 months. The solid black line represents the mean of the ensemble states, the (lower red) dashed line is the +1σ field model and the (upper red) dot-dashed line is the −1σ field model as calculated from the mean of the ensemble. Model I assumes that the forecast model uncertainties and the assimilated field model uncertainties are set to be approximately similar in magnitude. Model II has assimilated field model uncertainties that are approximately one-half the size of model I. The assimilated field model uncertainties for model III are approximately one-quarter the size of those in model I.