Evaluating Low-Cloud Simulation from an Upgraded Multiscale Modeling Framework Model. Part III Tropical and Subtropical Cloud Transitions over the Northern Pacific

• Published in: Journal of climate Vol. 26; no. 16; pp. 5761 - 5781
• Main Authors: Cheng, Anning, Xu, Kuan-Man
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01.08.2013
• Subjects: Aerosols; Agreements; Atmosphere; Atmospheric models; Bias; Boundary layers; Climate models; Climatology. Bioclimatology. Climate change; Cloud cover; Cloud parameterization; Clouds; Coastal environments; Computer simulation; Consistency; Convection clouds; Cumulus clouds; Decoupling; Earth, ocean, space; Exact sciences and technology; External geophysics; Fluxes; General circulation models; Geophysics. Techniques, methods, instrumentation and models; Humidity; Intercomparison; Liquids; Marine; Meteorology; Modeling; Modelling; Parameterization; Parametrization; Position (location); Precipitable water; Precipitation; Qualitative analysis; Radiation; Radiation-cloud interactions; Sea ice; Sea ice properties; Sea ice temperatures; Sea surface; Sea surface temperature; Seasonal variations; Seasons; Short wave radiation; Simulation; Simulations; Stratocumulus clouds; Surface temperature; Tropical environments; Water wells; Pacific Ocean; California; United States; North Pacific; INE, USA, California; Performance evaluation; Climatology; parametrization; General circulation models; Cloud resolving model; Atmospheric boundary layer; tropical zone; Climate models; digital simulation; clouds; subtropical zone; North America
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/JCLI-D-12-00650.1

An analysis of simulated cloud regime transitions along a transect from the subtropical California coast to the tropics for the northern summer season (June–August) is presented in this study. The Community Atmosphere Model, version 5 (CAM5), superparameterized CAM (SPCAM), and an upgraded SPCAM with intermediately prognostic higher-order closure (SPCAM-IPHOC) are used to perform global simulations by imposing climatological sea surface temperature and sea ice distributions. The seasonal-mean properties are compared with recent observations of clouds, radiation, and precipitation and with multimodel intercomparison results. There are qualitative agreements in the characteristics of cloud regimes along the transect among the three models. CAM5 simulates precipitation and shortwave radiative fluxes well but the stratocumulus-to-cumulus transition occurs too close to the coast of California. SPCAM-IPHOC simulates longwave radiative fluxes and precipitable water well, but with systematic biases in shortwave radiative fluxes. The broad, stronger ascending band in SPCAM is related to the large biases in the convective region but the characteristics of the stratocumulus region are still more realistic and the transition occurs slightly farther away from the coast than in CAM5. Even though SPCAM-IPHOC produces the most realistic seasonal-mean transition, it underestimates the mean gradient in low-cloud cover (LCC) across the mean transition location because of an overestimate of LCC in the transition and convective regions that shifts the transition locations farther from the coast. Analysis of two decoupling measures shows consistency in the mean location and the histogram of decoupling locations with those of LCC transition. CAM5, however, lacks such a consistency, suggesting a need for further refinement of its boundary layer cloud parameterization.