A two‐time‐level semi‐Lagrangian global spectral model

Abstract A three‐time‐level semi‐Lagrangian global spectral model was introduced operationally at the European Centre for Medium‐Range Weather Forecasts in 1991. This paper first documents some later refinements to the three‐time‐level scheme, and then describes its conversion to a two‐time‐level scheme. Experimental results are presented to show that the two‐time‐level scheme maintains the accuracy of its three‐time‐level predecessor, while being considerably more computationally efficient.