18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Tuesday, 31 July 2001
Mesoscale model evaluation of a new integration scheme for the Met Office Unified Model
Andrew J. Malcolm, UK Met Office, Bracknell, Berks., United Kingdom; and T. Davies, H. Lean, and P. Clark
Poster PDF (139.8 kB)
The Unified Model (UM) at the Met Office is designed to be applicable over a range of space and times scales; from mesoscale modeling to climate research.

A new integration scheme has been developed for the UM with the following features:

(i) Non-hydrostatic.

(ii) Height as vertical coordinate.

(iii) Charney-Phillips staggered vertical grid.

(iv) C grid staggered horizontal grid.

(v) Semi-Lagrangian advection scheme.

(vi) Semi-implicit without the removal of a basic state profile and with a 3-dimensional solver for a variable coefficient problem.

The new scheme has been coded to run efficiently on massively parallel machines and both the semi-Lagrangian scheme and the 3-d Helmholtz solver perform efficiently with excellent scalability demonstrated up to 576 processors.

The performance of the new scheme as a mesoscale forecast model/research tool has also been investigated. A member of the FASTEX IOP campaign has been used for investigation. The case has been run at horizontal resolutions from 12 km down to 1 km and with vertical resolutions from 38 to 90 levels. These tests have shown the frequency at which LBC's are needed and the decrease in timestep required. Many of the features of the flow appear to be better and realistically captured by the New Dynamics.

In other case study tests encouraging results have also been obtained in a study of widespread, persistent fog formation when run at 2km horizontal resolution.

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