Boundary Layer and Shallow Cumulus Clouds in a Medium-Range Forecast of a Large-Scale Weather System
Open Access
- 1 July 2005
- journal article
- Published by American Meteorological Society in Monthly Weather Review
- Vol. 133 (7), 1938-1960
- https://doi.org/10.1175/mwr2958.1
Abstract
The role and impact that boundary layer and shallow cumulus clouds have on the medium-range forecast of a large-scale weather system is discussed in this study. A mesoscale version of the Global Environmental Multiscale (GEM) atmospheric model is used to produce a 5-day numerical forecast of a midlatitude large-scale weather system that occurred over the Pacific Ocean during February 2003. In this version of GEM, four different schemes are used to represent (i) boundary layer clouds (including stratus, stratocumulus, and small cumulus clouds), (ii) shallow cumulus clouds (overshooting cumulus), (iii) deep convection, and (iv) nonconvective clouds. Two of these schemes, that is, the so-called MoisTKE and Kuo Transient schemes for boundary layer and overshooting cumulus clouds, respectively, have been recently introduced in GEM and are described in more detail. The results show that GEM, with this new cloud package, is able to represent the wide variety of clouds observed in association with the large-scale weather system. In particular, it is found that the Kuo Transient scheme is mostly responsible for the shallow/intermediate cumulus clouds in the rear portion of the large-scale system, whereas MoisTKE produces the low-level stratocumulus clouds ahead of the system. Several diagnostics for the rear portion of the system reveal that the role of MoisTKE is mainly to increase the vertical transport (diffusion) associated with the boundary layer clouds, while Kuo Transient is acting in a manner more consistent with convective stabilization. As a consequence, MoisTKE is not able to remove the low-level shallow cloud layer that is incorrectly produced by the GEM nonconvective condensation scheme. Kuo Transient, in contrast, led to a significant reduction of these nonconvective clouds, in better agreement with satellite observations. This improved representation of stratocumulus and cumulus clouds does not have a large impact on the overall sea level pressure patterns of the large-scale weather system. Precipitation in the rear portion of the system, however, is found to be smoother when MoisTKE is used, and significantly less when the Kuo Transient scheme is switched on.Keywords
This publication has 65 references indexed in Scilit:
- Operational Implementation of the ISBA Land Surface Scheme in the Canadian Regional Weather Forecast Model. Part I: Warm Season ResultsJournal of Hydrometeorology, 2003
- Operational Implementation of the ISBA Land Surface Scheme in the Canadian Regional Weather Forecast Model. Part II: Cold Season ResultsJournal of Hydrometeorology, 2003
- Operational Implementation of the Fritsch–Chappell Convective Scheme in the 24-km Canadian Regional ModelWeather and Forecasting, 2000
- An Examination of Local versus Nonlocal Aspects of a TKE-Based Boundary Layer Scheme in Clear Convective ConditionsJournal of Applied Meteorology and Climatology, 1999
- Organization and Representation of Boundary Layer CloudsJournal of the Atmospheric Sciences, 1998
- Precipitation in Stratocumulus Clouds: Observational and Modeling ResultsJournal of the Atmospheric Sciences, 1995
- Modeling of Trade Wind Cumuli with a Low-Order Turbulence Model: Toward a Unified Description of Cu and Se Clouds in Meteorological ModelsJournal of the Atmospheric Sciences, 1995
- A Model of Marine Boundary-Layer Cloudiness for Mesoscale ApplicationsJournal of the Atmospheric Sciences, 1992
- Small-Scale Variability in Warm Continental Cumulus CloudsJournal of the Atmospheric Sciences, 1985
- A Cumulus Parameterization Scheme Utilizing a One-Dimensional Cloud ModelMonthly Weather Review, 1977