Predictability of quasi-geostrophic planetary waves in global and hemispheric domains

Factors which affect the long term predictability, and also the feasibility of defining an ultimate level of weather predictability, are discussed. It is noted that current models yield a one week forecast at the best. Long range predictability, however, is a restriction on the knowledge of evolutive processes of the atmosphere, and does not characterize the prediction of specific atmospheric quantities. The influences of local phenomena such as cyclones and other nonlinear processes can cause planetary waves which affect the predictability of weather everywhere. It is suggested that any successful prediction model will necessarily account for the evolution of ultralong waves. Although significant differences in predictions have been found between hemispheric and global predictions, the location of the errors in extrapolating the hemispheric to the global scale have been identified.