Technical Report Series on Global Modeling and Data Assimilation, Volume 10: Dynamical Aspects of Climate Simulations Using the GEOS General Circulation Model

Technical Report · Mon Apr 01 04:00:00 EST 1996

OSTI ID:382990

Takacs, L L; Suarez, M J

The general circulation simulated by Version 1 of the Goddard Earth Observing System (GEOS-1) general circulation model is compared with the five-year reanalysis recently completed using the GEOS-1 data assimilation system. Emphasis is on the comparison of dynamical quantities, such as heat and momentum fluxes. The results indicate that, while many features are well simulated, the model exhibits a number of severe biases. These include: a cold bias at both poles and an associated westerly bias at upper levels, a strong low-level westerly bias during northern hemisphere winter, a dry tropical boundary layer and excessive moisture at all levels outside the tropics, too much poleward heat and momentum flux by transient eddies, and too little heat flux by stationary eddies. The effects on these biases of increasing resolution and order of accuracy, of including a parameterization of gravity wave drag, and of increasing the vertical extent of the model are also examined. The main impacts of increasing resolution and accuracy are found to be on the transient eddy statistics. The higher-order and higher-resolution experiments are in closer agreement with observations in the southern hemisphere, where the fluxes are primarily determined by the transient flow; however, in the northern hemisphere, where the fluxes due to the stationary flow are important, the more `accurate` simulations are systematically further from the analysis. As in several other studies, gravity wave drag is found to have a beneficial effect on both the time-mean flow and the transient statistics in the northern hemisphere, while little impact is seen in the southern hemisphere. Increasing the vertical extent of the model significantly improves the cold pole and westerly bias in the southern hemisphere.

• Research Organization: National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center
• OSTI ID: 382990
• Report Number(s): N--96-25891; NAS--1.15:104606; NIPS--96-43846; CNN: NAS5-32332
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ANNUAL VARIATIONS
ATMOSPHERIC CIRCULATION
BOUNDARY LAYERS
CLIMATE MODELS
G CODES
GENERAL CIRCULATION MODELS
GLOBAL ASPECTS
GRAVITY WAVES
HEAT FLUX
HUMIDITY
MOMENTUM TRANSFER
TEMPERATURE DEPENDENCE