A Cumulus Parameterization Study With Special Attention to the Arakawa-Schubert Scheme (semi-Prognostic, Meso-Scale Simulation)

222 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.Arakawa and Schubert (1974) developed a cumulus parameterization scheme in a framework that conceptually divides the mutual interaction of the cumulus convection and large-scale disturbance into the categories of large-scale budget requirements and the quasi-equilibrium assumption of cloud work function. We have applied the A-S scheme through a semi-prognostic approach to two different data sets: one is for an intense tropical cloud band event; the other is for tropical composite easterly wave disturbances. Both were observed in GATE. The cloud heating and drying effects predicted by the Arakawa-Schubert scheme are found to agree rather well with the observations. However, it is also found that the Arakawa-Schubert scheme underestimates both condensation and evaporation rates substantially when compared with the cumulus ensemble model results (Soong and Tao, 1980; Tao, 1983). An inclusion of the downdraft effects, as formulated by Johnson (1976), appears to alleviate this deficiency.In order to examine how the Arakawa-Schubert scheme works in a fully prognostic problem, a simulation of the evolution and structure of the tropical cloud band, mentioned above, under the influence of an imposed large-scale low-level forcing has been made, using a two-dimensional hydrostatic model with the inclusion of the Arakawa-Schubert scheme. Basically, the model result indicates that the meso-scale convective system is driven by the excess of the convective heating derived from the Arakawa-Schubert scheme over the adiabatic cooling due to the imposed large-scale lifting and induced meso-scale upward motion. However, as the convective system develops, the adiabatic warming due to the subsidence outside the cloud cluster gradually accumulates into a secondary temperature anomaly which subsequently reduces the original temperature contrast and inhibits the further development of the convective system. A 24 hour integration shows that the model is capable of simulating many important features such as the life cycle, intensity of circulation, and rainfall rates.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD