A comparison of cloud-resolving model simulations of trade wind cumulus with aircraft observations taken during RICO

This paper presents results from simulations of trade wind cumulus with the Met Office Large Eddy Model (LEM) based on observed environmental profiles from the Rain In Cumulus over the Ocean (RICO) field experiment. Comparisons of updraught core parameters are made with the in situ data collected onboard the three research aircraft that participated in RICO. The default set-up of the LEM was unable to produce sufficient amounts of rainwater content when compared to measurements by the aircraft. As a main aim of RICO was to quantify the importance of precipitation in the trade cumulus regime, we test the sensitivity of the model to changes in the rain microphysics, the large-scale forcing, and horizontal resolution. By changing these model variables we are able to obtain reasonably good agreement with the observations of updraught core vertical velocity, cloud and rainwater contents. Furthermore, the LEM produces comparable surface precipitation rates to those derived from radar measurements during RICO in a previous study. This gives us some confidence in the ability of the LEM to simulate realistic precipitating trade cumulus. (C) Crown Copyright 2007. Reproduced with the permission of the Controller of HMSO. Published by John Wiley & Sons, Ltd.