抄録
The reproducibility and future changes in the first baroclinic Rossby radius of the ocean in twenty atmosphere-ocean coupled general circulation models are investigated based on the Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset. For each of the models, the zonally averaged first baroclinic Rossby radius and the corresponding phase speed of long baroclinic Rossby waves simulated in the 20th century (20C3M) experiment are compared to their counterpart estimated from observed fields of temperature and salinity based on the World Ocean Atlas 2005. A tendency is found for these quantities to be better reproduced in higher-resolution models than in lower-resolution models. The response of the radius to the increasing atmospheric CO2 level is assessed for each of the models through comparison between the 20C3M and A1B experiments. In all the models, the zonally averaged first baroclinic Rossby radius increases by the late 21st century at almost all latitudes, but the magnitude of the projected increase varies from one model to another, for example, ranging from 2% to 20% as the relative change around 40°N. In the subtropics (equatorward of 45° latitude), the enhanced increase in the simulated first baroclinic Rossby radius due to the enhanced static stability in the upper ocean is attributable largely to the enhanced warming in the lower troposphere. At higher latitudes, in contrast, the enhanced static stability is more sensitive to the enhanced precipitation. Our result indicates that the propagation of oceanic Rossby waves is likely to be faster in the warmer climate, implying that the dominant time scale of extratropical low-frequency climate variability will likely shorten.
