Influence of stochastic physics on the frequency of occurrence of North Pacific weather regimes in the ECMWF model.

TitleInfluence of stochastic physics on the frequency of occurrence of North Pacific weather regimes in the ECMWF model.
Publication TypeTechnical memorandum
Date Published07/2005
Secondary TitleECMWF Technical Memorandum
Number473
AuthorsJung, T, Palmer, TN, Shutts, GJ
PublisherECMWF
Place PublishedShinfield Park, Reading
Abstract

One common problem of many atmospheric circulation models is that the strength of the mean westerly winds is overestimated in the mid-latitude North Pacific. This westerly wind bias is also a prominent feature in a recent version of the ECMWF model. Here we use the ECMWF model in order to investigate whether the use of stochastic physics helps reducing this error using the concept of weather regimes. The focus is on the winter season when the atmospheric regime structure is most pronounced. It is shown that the operational version of the ECMWF stochastic physics has little impact on the frequency of occurrence of North Pacific weather regimes. A recently developed scheme, however, which is based on combining a cellular automaton with a stochastic backscatter component, leads to substantial improvements in the simulation of the frequency of occurrence of North Pacific weather regimes.

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