Specification for LAM cold-air outbreak Case

We are trying to be as inclusive as possible so we will suggest two methods. The first is a forecast approach where a participant uses a global model forecast to derive LBCs. The second method is a 'nudging' approach that makes use of updated analyses at 6h intervals. Below we describe the setup for the LAM intercomparison, including the forcing for both methods and the required output

Time period

Model domain and resolution of inner domain

Outer domain - the outer nest(s) used to drive the inner domain described above will be left to the participants.

The vertical resolution and model timestep is not prescribed as part as the intercomparison set-up. The Met Office UM is using 70 Levels up to 40km and a 50 second timestep. We recommend that participants run at least one simulation with an operational level set and timestep, but if you have the option to experiment with different resolutions that will be welcome. We will interpolate onto a common vertical coordinate

Parametrization switches

For each of the LAM grid resolutions (1, 2, 4, 8, 16km) we would like to receive results from the two permutations of the convection off and on. One of these permutations may be the control setting for your model at that resolution. If so, please identify that for us. There might be other parameterizations that should be switched on or off. For instance your LAM might have a seperate shallow and deep cumulus convection scheme. Please feel free to experiment with different combinations of these parameterisations switched on and/or off

Forcing Data

Please contact Paul Field ( ) to obtain the ECMWF analysis data for the LAM set-up