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Background of the SCM case set up

Below we give a short summary of the methods used to derive the initial profiles and forcings for the RICO precipitating cumulus case.

Large scale forcings

Unlike the BOMEX case, for which accurate large scale forcings were obtained from an extensive set of observations, we were unable to deduce accurate reasonable forcings from the RICO observations. As an alternative, we used a RACMO HindCast to get estimates of the large scale forcings. The RACMO (Regional Atmospheric Climate Model) HindCast is a high-resolution version of the ECMWF model initialized every 24 hours with the ECMWF analysis at 12 UTC. The simulation was performed for a small domain, consisting of 90 x 92 gridpoints with a resolution of 20km, in which the RICO research area (61.46W, 17.97N) is contained.
A total period of 2 months (December 2004 and January 2005) was simulated, and output was generated every 10 minutes on a 5 x 5 grid centered around the RICO research area. The output includes, among others, large scale tendencies due to advection (a combined vertical and horizontal advection), vertical profiles of horizontal winds, temperature, moisture and vertical velocity and the precipitation at the surface. A time serie of the latter shows that the relative amount of precipitation produced in RACMO coincides reasonably well with the observations by the SPol radar (shown in the introduction), which gives us certain confidence in the the quality of the RACMO results for this undisturbed RICO period we are considering.

We use the obtained large-scale forcings to set up 2 experiments for the Single Column Models (SCM's) based on the undisturbed period from 16 December 2004 to 05 January 2005:

  • A short composite SCM run initialised with the mean state and driven by the mean large scale forcings based on the undisturbed 3 week period.

  • A long SCM run for the whole 3 week undisturbed period driven by the day to day varying large scale forcings as obtained from the high resolution hindcast.

For the composite run we derived the mean subsidence velocity profile and the mean large scale temperature and moisture tendencies due to horizontal advection. It is essentially the same case as the one designed for the LES models so for further details of the background of the set up we refer to the section with the LES model background . We urge the SCM modellers to do at least this composite case.

The case description for the short composite case can be found in Set up short composite run while the the case description for the long run is given in Set up long run. The reason for adding this long run is that mean atmospheric state that comes out as a response of the composite case is not necessarily the same atmospheric state that results from the day to day varying forcings over the 3 week period. The long SCM run is a bit controversial in the sense that we are not sure at this moment whether such a long run will drift away too much, especially in the upper troposphere and stratosphere. So SCM-ers are encouraged to investigate modifications for this case, for instance through nudging of the upper part of the atmosphere.