An efficient atmospheric boundary layer model for GCMs: Its design, validation, and implementation into the GISS-GCM

Thesis/Dissertation · Fri Dec 31 04:00:00 EST 1993

OSTI ID:106812

Zinn, H P

Climate prediction models need realistic descriptions of physical subgrid scale processes in order to provide reliable long-range global forecasts. This dissertation concerns the design, validation, and efficient implementation of a model for the Planetary Boundary Layer (PBL) for Global Circulation Models (GCMs). The project was motivated by the need for a better representation of the turbulent surface fluxes for heat and momentum. Special emphasis is placed in the PBL model on the realistic representation of the effects of thermal stratification and latitudinal variation. The new PBL model consists of a surface layer and a mixed layer with variable depth. The two domains are matched together with the conditions of constant momentum and heat flux. An algebraic solution to the mean momentum equations formulated as a symmetric rotating channel flow describes the mixed-layer velocity profile. Turbulent diffusion is modeled in the surface layer by a drag law and by a first-order closure model in the mixed layer and depends on thermal stratification. The coupled system is solved by an iterative method. In order to preserve the computational efficiency of the GISS-GCM, the new PBL model is implemented by means of look-up tables with the external parameters given by the bulk PBL Richardson number, PBL depth, neutral drag coefficient, and latitude. The diurnal cycle of PBL variables at some selected locations and their global distribution are compared between the GISS-GCM with the new PBL model (Model IIA) and Model II. The new PBL model responds more realistically to the external forcings than Model II. A multi-year simulation of Model IIA shows improved agreement with observed mean climatic quantities over Model II as seen in the mean January surface wind field and precipitation distribution. The new PBL model also affects the transient flow, as seen in the higher kinetic energy of the large-scale nonstationary eddies.

• Research Organization: Rutgers--the State Univ., New Brunswick, NJ (United States)
• OSTI ID: 106812
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
99 GENERAL AND MISCELLANEOUS
ATMOSPHERIC CIRCULATION
BOUNDARY LAYERS
DIFFUSION
GENERAL CIRCULATION MODELS
GREENHOUSE EFFECT
HEAT FLUX
ITERATIVE METHODS
TURBULENCE