抄録
We present a practical method to correct systematic errors of the predicted zonal mean field during a time integration of dynamical long-range forecasts. It is based on the fact that the first some spherical harmonic components with zonal wavenumber 0 of the observed temperature in the troposphere remain nearly unchanged with time. In this method, those components are not forecast but fixed to their initial values during the course of time integration. We applied the correction method to one-month forecast for the period from 17 December 1984 to 15 January 1985 using the JMA global spectral model.
It was found that forecast skill for ultralong waves was improved in the later part of the forecast period due to a better zonal mean forecast, but the effect was strongly dependent on the initial conditions. Systematic errors of the zonal mean surface pressure were not reduced by the present method.
