EUCLIPSE

1. Which value for the roughness length should be used?

For momentum and heat one should use z₀ = 2 10^-4 m.

2. What is the start time of the simulation?

In the current set-up the simulation should start at the time of the second flight (A209) of the Lagrangian, so this means that the simulation starts on 13 June 00 UTC. The rationale being that we now start with the same setting as Peter Duynkerke's A209 first ASTEX GCSS intercomparison case.

3. In the first round of the intercomparison study the prescribed large-scale divergence rate differed from the results found by Chris Bretherton.

We found that ECMWF (ERA-interim) results are different from the original ERA 40 results, and they also show a large temporal and spatial variation. Modelers are encouraged to do sensitivity tests with the subsidence rate.

4. The sea surface temperature is prescribed. Why not use the surface flux formulation proposed for the CGILS experiment where the flux is proportional to a constant and the difference between the lowest full level and the surface?

The CGILS drag coefficient implicitly includes a prescribed horizontal wind velocity. Moreover, the drag coefficient depends on the vertical grid resolution used. Therefore for now we do not request a particular surface flux scheme.

5. Who is going to participate?

The ASTEX intercomparison case is part of the EUCLIPSE project. This means that the UKMO, TU Delft, MPI-Hamburg and the University of Warzaw will run the case with LES models. In addition, the group of Chris Bretherton will also run the case. Also as part of EUCLIPSE several institutions will run Single-Column Model versions of weather prediction and climate models. Any modeler who has an interest to run these case is more than welcome to join.