An improved PDF cloud scheme for climate simulations

• Published in: Quarterly journal of the Royal Meteorological Society Vol. 136; no. 651; pp. 1583 - 1597
• Main Authors: Kuwano‐Yoshida, Akira, Enomoto, Takeshi, Ohfuchi, Wataru
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.07.2010; Wiley
• Subjects: AGCM; Boundary layer; Climate; Clouds; Computational fluid dynamics; Computer simulation; Earth, ocean, space; Exact sciences and technology; External geophysics; Horizontal; large‐scale condensation; marine boundary layer; Meteorology; Physics of the high neutral atmosphere; Probability density functions; stratus; Turbulence; Atmosphere model; General circulation models; sensitivity analysis; marine boundary layer; Gaussian distribution; Probability distribution; digital simulation; clouds; AGCM; Mixing length; stratus; Large eddy simulation; Potential temperature; condensation; Distribution function; water content; Turbulence energy; stability; large-scale condensation; Climate models; Joint distribution; turbulence; Mixed layer; Atmospheric boundary layer; atmospheric circulation
• ISSN: 0035-9009; 1477-870X; 1477-870X
• DOI: 10.1002/qj.660

An efficient grid‐scale cloud scheme for climate simulation is implemented in the atmospheric general circulation model for the Earth Simulator (AFES). The new cloud scheme uses statistical partial condensation using joint‐Gaussian probability distribution functions (PDFs) of the liquid water potential temperature and total water content, with standard deviations estimated by the moist Mellor–Yamada level‐2 turbulence scheme. It also adopts improved closure parameters based on large‐eddy simulations and a revised mixing length that varies with the stability and turbulent kinetic energy. These changes not only enable better representation of low‐level boundary layer clouds, but also improve the atmospheric boundary layer structure. Sensitivity experiments for vertical resolution suggest that O(100–200 m) intervals are adequate to represent well‐mixed boundary layers with the new scheme. The new scheme performs well at relatively low horizontal resolution (about 150 km), although inversion layers near the coast become more intense at a higher horizontal resolution (about 50 km). Copyright © 2010 Royal Meteorological Society