Towards an operational 1km limited area model by using variable resolution

The Met Office Unified model (UM) has a non-hydrostatic formulation, which offers the scope to run forecasts at very high resolution. A Limited Area Model with a horizontal resolution of 4km was introduced operationally in 2006 and a 1.5km version of the model is available to forecasters on demand. In research mode the model has been run with a horizontal resolution of 100 metres.

Also under development is a variable resolution version of the UM for a limited area domain. The plan is to embed an area of high resolution (1km) inside a domain of lower resolution (4km) with an intervening area where the mesh changes in a constant ratio. This should allow the UM to run higher resolution over areas of interest at much lower cost than running at high resolution everywhere.

We will show timings for the model under development and also show results from a test case to demonstrate the approach works.