Similarity of 'fast-growing perturbations' and an illustrative experiment with ensemble forecasting

Abstract

We address an aspect of the role that ensemble forecasting may play in five-day forecasts both globally and over the Australian region. A central question that arises in this topic is how to choose the most useful perturbations from which to run the ensemble. The philosophy adopted here is that the 'best' perturbations are those that are representative of the analysis errors and that project onto growing synoptic modes. Such perturbation modes are found using a method designed to 'breed' a perturbation that is representative of errors introduced in an analysis cycle. These fast-growing modes (FGMs) are discussed in terms of both synoptic variability and within a theoretical framework of the ..