Ultralong atmospheric waves and a long-range forecasting

Abstract

A hydrodynamic model of a long-range forecasting of planetary waves is described. In developing this model a priori meteorological information together with the theory of atmospheric instability was used. To solve the filtered multi-level model the spectral method of spherical harmonics was applied. The most large-scale harmonics of “climatic sources” were computed from the acquired data on the state of the atmosphere during a long period of time. Heating and dissipation were estimated with the help of considerable a priori information. Two series of 10-day forecasts based on real initial data are described with a truncated model with 15 (F-15) and 81 (F-81) spherical harmonics. Zonal wave numbers m = 0, 1 and 2 are involved in the first variant of the model while m = 0, 1, 2, …, 8 are used in the second. If during the time integration there occurs a loss of motion stability in respect to long waves, the F-81 model gives worse forecast errors than the F-15 does; in the other cases the F-81 model provides a better forecast of mean zonal motion and of the longest waves (in all the forecasts the first fifteen spherical harmonics were compared). For the forecasts in the stratosphere a model is given which allows the forecast errors of the mean zonal motion and ultralong waves to be decreased in cases when the estimation of the nonlinear operator of the model by numerical integration shows that the forecast problem becomes conditionally correct, i.e. corrent only for the most large-scale perturbations.