How Well Can We Represent the Spectrum of Convective Clouds in a Climate Model? Comparisons between Internal Parameterization Variables and Radar Observations

Journal Article · Tue May 01 00:00:00 EDT 2018 · Journal of the Atmospheric Sciences

DOI:https://doi.org/10.1175/JAS-D-17-0191.1· OSTI ID:1435391

Labbouz, Laurent ^[1]; Kipling, Zak ^[1]; Stier, Philip ^[1]; Protat, Alain ^[2]

---

1. Department of Physics, University of Oxford, Oxford, United Kingdom
2. Bureau of Meteorology, Melbourne, Victoria, Australia

Current climate models cannot resolve individual convective clouds, and hence parameterizations are needed. The primary goal of convective parameterization is to represent the bulk impact of convection on the gridbox-scale variables. Spectral convective parameterizations also aim to represent the key features of the subgrid-scale convective cloud field such as cloud-top-height distribution and in-cloud vertical velocities in addition to precipitation rates. Ground-based radar retrievals of these quantities have been made available at Darwin, Australia, permitting direct comparisons of internal parameterization variables and providing new observational references for further model development. A spectral convective parameterization [the convective cloud field model (CCFM)] is discussed, and its internal equation of motion is improved. Results from the ECHAM–HAM model in single-column mode using the CCFM and the bulk mass flux Tiedtke–Nordeng scheme are compared with the radar retrievals at Darwin. The CCFM is found to outperform the Tiedtke–Nordeng scheme for cloud-top-height and precipitation-rate distributions. Radar observations are further used to propose a modified CCFM configuration with an aerodynamic drag and reduced entrainment parameter, further improving both the convective cloud-top-height distribution (important for large-scale impact of convection) and the in-cloud vertical velocities (important for aerosol activation). This study provides a new development in the CCFM, improving the representation of convective cloud spectrum characteristics observed in Darwin. This is a step toward an improved representation of convection and ultimately of aerosol effects on convection. It also shows how long-term radar observations of convective cloud properties can help constrain parameters of convective parameterization schemes.

• Research Organization: Bureau of Meteorology, Melbourne, VIC (Australia); Univ. of Oxford (United Kingdom)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER); European Research Council (ERC)
• Grant/Contract Number: FG02-03ER63533; FG02-08ER64527; 603445; FP7–280025; 724602
• OSTI ID: 1435391
• Alternate ID(s): OSTI ID: 1509850
• Journal Information: Journal of the Atmospheric Sciences, Journal Name: Journal of the Atmospheric Sciences Vol. 75 Journal Issue: 5; ISSN 0022-4928
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
maritime continent
convective clouds
precipitation
radars/radar observations
convective parameterization
single column models