Triggering of boundary layer cumulus clouds over a heterogeneous surface

Conference · Sat Apr 01 04:00:00 EST 1995

OSTI ID:83197

Schrieber, K; Stull, R; Zhang, Q ^[1]

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1. Univ. of Wisconsin, Madison, WI (United States)

Complex multimodal joint frequency distributions of LCL height versus {theta}{sub v} in surface-layer air over a large heterogeneous surface area are modeled as the superposition of simpler mono-modal distributions. These simpler distributions, which apply to quasi-homogeneous subdomains, are approximated with bivariate distribution models. The shape of each of these modeled distributions depends on variations of the Bowen ratio and heat input forcings. These forcings are a function of the landscape, insolation, surface albedo, cloud-shading, soil moisture, and other factors that either are known as imposed boundary conditions or can be resolved or parameterized on the coarse grid scale of a global climate forecast model (GCM). This approach is motivated by the need to forecast subgrid-scale boundary-layer cumulus clouds in GCMs and in one-dimensional (single column) forecast models. The full distribution function, formed as a composite from the simpler models, can be combined with mean virtual temperature sounding information to forecast cloud onset time, cloud coverage, cloud base and heights, and cloud size distributions of an ensemble of subgrid clouds. Thus, land-use inventories or similar satellite-based observations of relative landscape amounts have the potential to be combined with distribution parameterizations such as those explored to forecast subgrid clouds. As a case study, we have analyzed aircraft data from the Hydrologic Atmospheric Pilot Experiment (HAPEX) field experiment in southwest France, which was designed to answer basic questions about GCM subgrid modeling within a horizontal grid area 100 km on a side. For this data set, we found that bivariate range-cut Gaussian or pq distribution models work equally well to approximate the simpler mono-modal distributions within quasi homogeneous subdomains.

• Research Organization: USDOE Office of Energy Research, Washington, DC (United States). Environmental Sciences Div.
• DOE Contract Number: FG02-92ER61361
• OSTI ID: 83197
• Report Number(s): CONF-940277--; ON: DE95009951
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AIR-BIOSPHERE INTERACTIONS
ALBEDO
BOUNDARY CONDITIONS
CLOUDS
COMPLEX TERRAIN
GENERAL CIRCULATION MODELS
PARAMETRIC ANALYSIS