Regional Climate Modeling over the Maritime Continent. Part II New Parameterization for Autoconversion of Convective Rainfall

• Published in: Journal of climate Vol. 27; no. 4; pp. 1504 - 1523
• Main Authors: Gianotti, Rebecca L., Eltahir, Elfatih A. B.
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01.02.2014
• Subjects: Biosphere; Climate; Climate change; Climate models; Climatology. Bioclimatology. Climate change; Cloud cover; Cloud droplets; Cloud water; Clouds; Colleges & universities; Construction; Convection; Convection clouds; Convective clouds; Convective rainfall; Droplets; Earth, ocean, space; Enthalpy; Exact sciences and technology; External geophysics; Geophysics. Techniques, methods, instrumentation and models; Mathematical models; Meteorology; Methods; Modeling; Modelling; Moisture content; Net radiation; Oceans; Parameterization; Parametrization; Performance evaluation; Precipitation; Radiation balance; Rain; Rainfall; Rainfall intensity; Regional climate models; Regional climates; Sensible heat; Short wave radiation; Simulation; Simulations; Simulators; Surface fluxes; Variability; Variables; Water; Water content; Water density; Asia; South east Asia; Oceania; United States > US; Colorado; Coupled model; rainfall; Water drop; parametrization; atmospheric precipitation; droplets; Regional scope; Convective precipitation; Convective cloud; Climate models
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/jcli-d-13-00171.1

This paper describes a new method for parameterizing the conversion of convective cloud liquid water to rainfall (“autoconversion”) that can be used within large-scale climate models, and evaluates the new method using the Regional Climate Model, version 3 (RegCM3), coupled to the land surface scheme Integrated Biosphere Simulator (IBIS). The new method is derived from observed distributions of cloud water content and is constrained by observations of cloud droplet characteristics and climatological rainfall intensity. This new method explicitly accounts for subgrid variability with respect to cloud water density and is independent of model resolution, making it generally applicable for large-scale climate models. This work builds on the development of a new parameterization method for convective cloud fraction, which was described in Part I. Simulations over the Maritime Continent using the Emanuel convection scheme show significant improvement in model performance, not only with respect to convective rainfall but also in shortwave radiation, net radiation, and turbulent surface fluxes of latent and sensible heat, without any additional modifications made to the simulation of those variables. Model improvements are demonstrated over a 19-yr validation period as well as a shorter 4-yr evaluation. Model performance with the Grell convection scheme is not similarly improved and reasons for this outcome are discussed. This work illustrates the importance of representing observed subgrid-scale variability in diurnally varying convective processes for simulations of the Maritime Continent region.