HR: 1340h
AN: P33C-0252    [Abstracts]
TI: Numerical Modeling of Cloud Convection in Titan's Atmosphere and its Role in Methan Hydrological Cycle
AU: * Nakajima, K
EM: kensuke@geo.kyushu-u.ac.jp
AF: Faculty of Science, Kyushu Univ., Fukuoka, 812-8581 Japan
AU: Ishiwatari, M
EM: momoko@ees.hokudai.ac.jp
AF: Graduate School of Environmental Earth Science, Hokkaido Univ., Sapporo, 060-0810 Japan
AU: Takehiro, S
EM: takepiro@gfd-dennou.org
AF: Research Inst. of Mathematical Sci., Kyoto Univ., Kyoto, 606-8502 Japan
AU: Hayashi, Y
EM: shosuke@gfd-dennou.org
AF: Graduate School of Sciences, Hokkaido Univ., Sapporo, 060-0810 Japan
AB: Distinct cloud activities are found around the south pole of Titan, and their transient characteristics imply their convective origin. On the other hand, once proposed extensive hydrocarbon ocean, which might act as a reservoir of methane, seems to be absent. Therefore, the structure of cloud convection and its role in "hydrological" cycle may be quite different from the convective clouds in the atmosphere of the Earth, which are covered with the widespread ocean. Here, we examine the structure of cloud convection in Titan's troposphere and its role in methan cycle between the atmosphere and the ground surface by using a numerical model. We conduct long-term integrations of a two-dimensional non-hydrostatic cloud convection model that extends 2,048km in the horizontal direction including three-category (vapor-cloud-rain) parameterized microphysics. The supply of methane from the groud surface is caculated by the bulk formula, including a factor representing the wetness of the ground surface which may be interpreted as the ratio of the area of methane ponds to the area of dry soil. We also compare the case with and without the super saturation threshold for the condensation of methane in Titan's troposphere. In the model, the relative humidity in the lower atmosphere tends to be considerably higher than the observerd values, unless the wetness facter is very small (~ 0.001), which is consistent with the observed scarcity of the liquid surface. Even with such dry surface condition, simulated cloud convection is active; sometimes strong convective cloud develops up to the tropopause generating a large amount of methane rain. But very small amount of methane rain reaches to the ground surface as a result of the evaporation in the subsaturated lower troposphere. This is compatible with the small amount of evaporation in the model. In the case with the condensation threshold, the cloud convection tends to be more intermittent and stronger than that without it, so that larger amount of rain reaches to the ground surface.
UR: http://gfd.geo.kyushu-u.ac.jp/
DE: 3314 Convective processes
DE: 5405 Atmospheres (0343, 1060)
DE: 5445 Meteorology (3346)
DE: 5470 Surface materials and properties
DE: 6281 Titan
SC: Planetary Sciences [P]
MN: Fall Meeting 2005