Numerical investigations with a hybrid isentropic-sigma model. Part II: The inclusion of moist processes

• Published in: Journal of the atmospheric sciences 1991-01, Vol.48 (18), p.2025-2043
• Main Authors: Zapotocny, Tom H, Johnson, Donald R, Reames, Fred M, Pierce, RBradley, Wolf, Bart J
• Format: Article
• Language: English
• ISSN: 0022-4928

The main goals of this paper are 1) to demonstrate the feasibility of incorporating a prognostic equation for water vapor and diabatic processes in the University of Wisconsin theta - sigma model discussed in Part I, 2) to document methods applied to overcome difficulties stemming from the inclusion of moist processes, and 3) to present results illustrating the effects of latent heat release on baroclinic development. The results confirm earlier studies that a prognostic equation for water vapor and the diabatic component of latent heat release may be included in a hybrid model. However, the modifications made in this study were important for eliminating spurious supersaturation and release of latent heat within grid volumes emerging and submerging through the interface between sigma and isentropic model domains. The results demonstrate the hybrid model's robust nature and potential for use in prediction. For this demonstration, model simulations of an analytically specified synoptic-scale wave that amplified baroclinically under dry and moist conditions are compared. Simulations with and without a hydrological component show that the overall effect of latent heat release is to markedly enhance cyclo- and frontogenesis. The resultant pattern of precipitation is coherent, and the structure of the developing wave is consistent with the concepts of self-development. No detrimental effects are evident in either the structure or processes resulting from the inclusion of moist processes and the presence of an interface between sigma and isentropic model domains.