B115 放射対流平衡大気中の放射駆動循環

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To investigate water vapor transport in an atmosphere in radiative-convective equilibrium, we constructed a simplified dynamical convection model (DCM) that explicitly models moist convection and longwave radiation in a gray atmosphere. In the subsidence region of the equilibrium atmosphere predicted by the DCM, dynamical heating and radiative cooling balance. Subsidence that satisfies local thermodynamical balance includes detrainment from adjacent cumulus updraft at all levels in the free troposphere, from high levels with a small absolute humidity to low levels with a large absolute humidity. In this subsidence region, absolute humidity increases downward, but relative humidity is approximately constant with height. This contrasts sharply with results from a cumulus chimney model (CCM) that limits detrainment to near the tropopause and produces drying in the free troposphere. To demonstrate the accuracy of the transport mechanism implied by the DCM, we examined results from a kinematic circulation model (KCM). The KCM and the DCM both produced an atmosphere far moister than predicted by the CCM. The feature of the detrainment at all levels of the free troposphere under a normal atmospheric situation does not depend on the radiation schemes used in the models. The relative humidity in the subsidence region in the free troposphere has a mostly uniform vertical profile and the mean value in the horizontal is independent of the horizontal scale. Water vapor transport moistens the atmosphere, preventing the excess drying that occurs in the CCM.
日本流体力学会の論文
2001-07-31

B115 放射対流平衡大気中の放射駆動循環

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