Numerical framework and performance of the new multiple-phase cloud microphysics scheme in RegCM4.5: precipitation, cloud microphysics, and cloud radiative effects

Abstract

Abstract. We implement and evaluate a new parameterization scheme for stratiform cloud microphysics and precipitation within regional climate model RegCM4. This new parameterization is based on a multiple-phase one-moment cloud microphysics scheme built upon the implicit numerical framework recently developed and implemented in the ECMWF operational forecasting model. The parameterization solves five prognostic equations for water vapour, cloud liquid water, rain, cloud ice, and snow mixing ratios. Compared to the pre-existing scheme, it allows a proper treatment of mixed-phase clouds and a more physically realistic representation of cloud microphysics and precipitation. Various fields from a 10-year long integration of RegCM4 run in tropical band mode with the new scheme are compared with their counterparts using the previous cloud scheme and are evaluated against satellite observations. In addition, an assessment using the Cloud Feedback Model Intercomparison Project (CFMIP) Observational Simulator Package (COSP) for a 1-year sub-period provides additional information for evaluating the cloud optical properties against satellite data. The new microphysics parameterization yields an improved simulation of cloud fields, and in particular it removes the overestimation of upper level cloud characteristics of the previous scheme, increasing the agreement with observations and leading to an amelioration of a long-standing problem in the RegCM system. The vertical cloud profile produced by the new scheme leads to a considerably improvement of the representation of the longwave and shortwave components of the cloud radiative forcing.

Air quality and climate change, Topic 3 of the Model Inter-Comparison Study for Asia Phase III (MICS-Asia III) – Part 1: Overview and model evaluation

“…Aerosols in RIEMS-Chem include sulfate, nitrate, ammonium, BC, OC, SOA, five bins of soil dust and five bins of sea salt (Han et al, 2012;Li and Han, 2016). ISORROPIA (Nenes et al, 1998) was coupled to RIEMS-Chem to treat thermodynamic equilibrium process and to simulate inorganic aerosols. SOA production from primary anthropogenic and biogenic VOCs is calculated using a bulk aerosol yield method according to Lack et al (2004).…”

“…In the atmosphere, SOA is mainly formed from the condensation of semi-volatile VOCs, which are the products of the oxidation of primary VOCs. An em-pirical two-product model (Odum et al, 1996) is often used to simulate SOA formation, but this method was reported to significantly underestimate measured SOA mass concentrations (Heald et al, 2008). Later, the volatility basis-set (VBS) approach (Donahue et al, 2006) was developed to represent the wide range of the volatility of organic compounds and complex processes.…”

Influence of cumulus convection schemes on winter North Pacific storm tracks in the regional climate model RegCM4.5

“…However, due to the computational level, the complexity of cloud microphysical processes and the complex relationship between cumulus scale and large‐scale circulation, many CCSs are still summarized from experience (Arakawa, ). Convective clouds are represented by cumulus parameterizations, which mostly focus on dynamical and thermodynamical processes and treat the cloud microphysics in simplified ways (Nogherotto et al ., ). The characteristics of the CCSs are under certain closed assumptions, and the convection triggering function is defined through some assumptions.…”

“…Nogherotto et al . () and Yang et al . (; ) have both provided a more detailed introduction to RegCM4.5.…”

“…The RegCM series model, developed by Abdus Salam International Center for Theoretical Physics, is a widely used system that has been applied to local and regional seasonal forecasting and climate change problems for all regions of the globe (Nogherotto et al ., ). Based on the Mesoscale Model version 4 (MM4) and the global spectrum model Community Climate Model (CCM1) from the National Center for Atmospheric Research, Dickinson et al .…”