"Cloud convections" in geophysical and planetary fluids
|Kensuke Nakajima (Faculty of Science, Kyushu Univ.)
Shin-ichi Takehiro (Faculty of Science, Kyushu Univ.)
Masaki Ishiwatari (Graduate school of Earth Environmental Science, Hokkaido Univ.)
Yoshi-Yuki Hayashi (Graduate School of Mathematical Sciences, Univ. of Tokyo)
In order to investigate diversity among convections observed in geophysical and planetary fluids, we conducted numerical experiments on convections with different specifications of phase changes in the fluid. Two of the parameters governing the effect of phase change, i.e., the relative weight of the condensible component, and the sign of vertical motion that causes saturation, are varied. The specification for each of the three experiments corresponds to cloud convection in the earth's atmosphere, cloud convection in jupiter's atmosphere, and convection in the earth's outer core.
In a situation where the condensible component that is lighter than the major components condenses in the updraft, a situation corresponding to earth's cloud convections, the simulated convection is characterized by the asymmetry between a strong, narrow updraft and a weak, widespread downdraft. Fluid motion is unsteady. When the gravitational sedimentation of the condensed phase is switched-off, the upward and downward motions in the convection are symmetric.
In a situation where the condensible component is heavier than the major components, a situation corresponding to the cloud convections in Jupiter's atmosphere, the characteristics of convection depends on the mixing ratio of the condensible component. When the mixing ratio is small, the structure of convection is similar to that in a situation where the condensible component is lighter. On the other hand, when the mixing ratio is large enough, convection does not occur in the lower portion of the condensing layer.
In a situation where the condensible component that is heavier than the major components condenses in the downdraft, a situation corresponding to the convection in the earth's outer core, steady convection with horizontally elongated cells are realized. The buoyancy source, resulting from gravitational sedimentation of the condensed phase, is distributed extensively in the lowermost layer, so that the overall configuration is similar to the convection with a constant heat flux boundary condition.
|(Received 31 January, 1998; in revised form 11 May, 1998)|