Search Results
You are looking at 1 - 2 of 2 items for :
- Author or Editor: L. Terray x
- Monthly Weather Review x
- Refine by Access: All Content x
Abstract
The authors present the distribution of a coupled ocean–atmosphere global circulation model. The atmospheric (ARPEGE) and the oceanic (OPA) components run separately at different sites; the coupling is achieved through the exchanges of fluxes via the coupler (OASIS) and the three independent programs communicate together through the 2-Mbit RENATER network. The coupling and distributing procedure is based on the PVM software and is validated by 1-yr simulations. Performances and difficulties raised by the distributed environment are also presented.
An additional study deals with the sensitivity to the precision in exchanged data in coupled mode. This question is addressed by introducing small artificial perturbations into the forcings of each component. The transient growth of these perturbations is first followed over 10 days on specific grid points. A global spatio-temporal analysis is then performed over the planet for 1-yr simulations.
During the first 10 days of the experiments, the “error” dynamics is amplified by the atmosphere with a doubling time of the order of 5 days, while the upper ocean simply relaxes toward equilibrium. For long time ranges of simulation, errors tend to saturate and oscillate around a plateau, following the seasonal cycle. Spatio-temporal studies prove that the most sensitive areas to the precision in exchanged forcings are related to the regions where the variability is the most pronounced. These analyses are integrated into the general studies of predictability in coupled ocean–atmosphere models.
Abstract
The authors present the distribution of a coupled ocean–atmosphere global circulation model. The atmospheric (ARPEGE) and the oceanic (OPA) components run separately at different sites; the coupling is achieved through the exchanges of fluxes via the coupler (OASIS) and the three independent programs communicate together through the 2-Mbit RENATER network. The coupling and distributing procedure is based on the PVM software and is validated by 1-yr simulations. Performances and difficulties raised by the distributed environment are also presented.
An additional study deals with the sensitivity to the precision in exchanged data in coupled mode. This question is addressed by introducing small artificial perturbations into the forcings of each component. The transient growth of these perturbations is first followed over 10 days on specific grid points. A global spatio-temporal analysis is then performed over the planet for 1-yr simulations.
During the first 10 days of the experiments, the “error” dynamics is amplified by the atmosphere with a doubling time of the order of 5 days, while the upper ocean simply relaxes toward equilibrium. For long time ranges of simulation, errors tend to saturate and oscillate around a plateau, following the seasonal cycle. Spatio-temporal studies prove that the most sensitive areas to the precision in exchanged forcings are related to the regions where the variability is the most pronounced. These analyses are integrated into the general studies of predictability in coupled ocean–atmosphere models.
Abstract
The seasonal cycle over the tropical Pacific simulated by 11 coupled ocean–atmosphere general circulation models (GCMs) is examined. Each model consists of a high-resolution ocean GCM of either the tropical Pacific or near-global means coupled to a moderate- or high-resolution atmospheric GCM, without the use of flux correction. The seasonal behavior of sea surface temperature (SST) and eastern Pacific rainfall is presented for each model.
The results show that current state-of-the-art coupled GCMs share important successes and troublesome systematic errors. All 11 models are able to simulate the mean zonal gradient in SST at the equator over the central Pacific. The simulated equatorial cold tongue generally tends to be too strong, too narrow, and extend too far west. SSTs are generally too warm in a broad region west of Peru and in a band near 10°S. This is accompanied in some models by a double intertropical convergence zone (ITCZ) straddling the equator over the eastern Pacific, and in others by an ITCZ that migrates across the equator with the seasons; neither behavior is realistic. There is considerable spread in the simulated seasonal cycles of equatorial SST in the eastern Pacific. Some simulations do capture the annual harmonic quite realistically, although the seasonal cold tongue tends to appear prematurely. Others overestimate the amplitude of the semiannual harmonic. Nonetheless, the results constitute a marked improvement over the simulations of only a few years ago when serious climate drift was still widespread and simulated zonal gradients of SST along the equator were often very weak.
Abstract
The seasonal cycle over the tropical Pacific simulated by 11 coupled ocean–atmosphere general circulation models (GCMs) is examined. Each model consists of a high-resolution ocean GCM of either the tropical Pacific or near-global means coupled to a moderate- or high-resolution atmospheric GCM, without the use of flux correction. The seasonal behavior of sea surface temperature (SST) and eastern Pacific rainfall is presented for each model.
The results show that current state-of-the-art coupled GCMs share important successes and troublesome systematic errors. All 11 models are able to simulate the mean zonal gradient in SST at the equator over the central Pacific. The simulated equatorial cold tongue generally tends to be too strong, too narrow, and extend too far west. SSTs are generally too warm in a broad region west of Peru and in a band near 10°S. This is accompanied in some models by a double intertropical convergence zone (ITCZ) straddling the equator over the eastern Pacific, and in others by an ITCZ that migrates across the equator with the seasons; neither behavior is realistic. There is considerable spread in the simulated seasonal cycles of equatorial SST in the eastern Pacific. Some simulations do capture the annual harmonic quite realistically, although the seasonal cold tongue tends to appear prematurely. Others overestimate the amplitude of the semiannual harmonic. Nonetheless, the results constitute a marked improvement over the simulations of only a few years ago when serious climate drift was still widespread and simulated zonal gradients of SST along the equator were often very weak.
