Inclusion of a prognostic cloud scheme with the relaxed Arakawa-Schubert cumulus parametrization: Single-column model studies

A prognostic cloud-prediction scheme has been tested with the relaxed Araka wa-Schubert cumulus-parametrization scheme using the GATE phase III data se t. Observed profiles of temperature, moisture and wind fields have been use d as initial conditions for a semi-prognostic as well as a fully prognostic study. The subsequent profiles of cloud liquid-water/ice, cloud fraction a nd precipitation rates besides several other fields have been generated by using these schemes. The cloud water substance and the cloud mass fraction are allowed to evolve prognostically along with the temperature and moistur e fields. Results indicate that errors in the temperature and moisture prof iles are lowest when the cloud scheme is allowed to interact with radiation and downdraughts are included in the model. Sensitivity studies have been carried out to understand the role of cloud-top entrainment instability. Re sults indicate that the cloud-top entrainment instability leads to a reduct ion of the cloud mass fraction and liquid-water content by 5-10% due to mix ing with the environment.