Geographically versus dynamically defined boundary layer cloud regimes and their use to evaluate general circulation model cloud parameterizations

• Published in: Geophysical research letters 2013-09, Vol.40 (18), p.4951-4956
• Main Authors: Nam, Christine C.W., Quaas, Johannes
• Format: Article
• Language: English
• Subjects: Altitude; Atmospheric stability; boundary layer clouds; Boundary layers; Circulation; Clouds; CloudSat; Computer simulation; Contamination; COSP; Cumulus clouds; Dynamic tests; Earth sciences; Earth, ocean, space; ECHAM5; Evaluation; Exact sciences and technology; General circulation; General circulation models; Histograms; Hydrometeors; Identification; Parametrization; Profiles; Radar; radar simulator; Reflectance; Reflectivity; Regional; Regional analysis; Simulation; Simulators; Stability; Stratocumulus clouds; Subsidence; Tropical climate; tropical low clouds
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/grl.50945

Regimes of tropical low‐level clouds are commonly identified according to large‐scale subsidence and lower tropospheric stability (LTS). This definition alone is insufficient for the distinction between regimes and limits the comparison of low‐level clouds from CloudSat radar observations and the ECHAM5 GCM run with the COSP radar simulator. Comparisons of CloudSat radar cloud altitude‐reflectivity histograms for stratocumulus and shallow cumulus regimes, as defined above, show nearly identical reflectivity profiles, because the distinction between the two regimes is dependent upon atmospheric stability below 700 hPa and observations above 1.5 km. Regional subsets, near California and Hawaii, for example, have large differences in reflectivity profiles than the dynamically defined domain; indicating different reflectivity profiles exist under a given large‐scale environment. Regional subsets are better for the evaluation of low‐level clouds in CloudSat and ECHAM5 as there is less contamination between 2.5 km and 7.5 km from precipitating hydrometeors which obscured cloud reflectivities. Key Points Identification of low clouds by large‐scale dynamics insufficient for radarStratocumulus and shallow cumulus regimes have nearly identical reflectivitiesGeographical regions are better for evaluating low-level clouds with a radar