Yoshiyuki O. Takahashi

Numerical Modeling for Venus Atmosphere Based on AFES (Atmospheric GCM for the Earth Simulator)

In order to elucidate phenomena of Venus atmosphere, an atmospheric general circulation model (AGCM) for Venus is being developed on the basis of AFES (AGCM For the Earth Simulator). As a first step toward high resolution numerical simulation with realistic physical processes, we investigate unstable modes on the condition of super-rotation by nonlinear numerical simulation with simplified physical processes. At initial state zonal super-rotation is assumed to exist. We use the relaxation forcing of the meridional temperature gradient to maintain the zonal flow. In the time evolution of this experimental setting, baroclinic modes grow in the cloud layer with small static stability. The structures of unstable modes are similar to those obtained in the linear stability analysis. We discuss resolution dependency of the results.

A Numerical Study of Convection in a Condensing CO2 Atmosphere under Early Mars-Like Conditions

AbstractCloud convection of a CO2 atmosphere where the major constituent condenses is numerically investigated under a setup idealizing a possible warm atmosphere of early Mars, utilizing a two-dimensional cloud-resolving model forced by a fixed cooling profile as a substitute for a radiative process. The authors compare two cases with different critical saturation ratios as condensation criteria and also examine sensitivity to number mixing ratio of condensed particles given externally.When supersaturation is not necessary for condensation, the entire horizontal domain above the condensation level is continuously covered by clouds irrespective of number mixing ratio of condensed particles. Horizontal-mean cloud mass density decreases exponentially with height. The circulations below and above the condensation level are dominated by dry cellular convection and buoyancy waves, respectively.When 1.35 is adopted as the critical saturation ratio, clouds appear exclusively as intense, short-lived, quasi-period...