A Numerical Study of Convection in a Condensing CO2 Atmosphere under Early Mars-Like Conditions
A Numerical Study of Convection in a Condensing CO2 Atmosphere under Early Mars-Like Conditions
复制标题
早期类火星条件下凝结二氧化碳大气中对流的数值研究
DOI：
10.1175/jas-d-15-0132.1
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发表时间：
2016
影响因子：
3.1
通讯作者：
Y.
中科院分区：
文献类型：
--
作者：
Yamashita;T.;Odaka;M.;Sugiyama;K.;Nakajima;K.;Ishiwatari;M.;Nishizawa;S.;Takahashi;Y. O. and Hayashi;Y.
在一个理想化的火星早期可能的温暖大气环境下，利用固定冷却剖面强制的二维云分辨模型，对主要成分凝结的二氧化碳大气的云对流进行了数值研究，以替代辐射过程。作者比较了两种不同临界饱和比作为凝聚标准的情况，并考察了外界给定的凝聚颗粒数混合比的敏感性。当冷凝不需要过饱和时，无论冷凝颗粒的数量混合比如何，冷凝水平以上的整个水平区域都连续被云覆盖。水平平均云团密度随高度呈指数递减。凝结层以下和凝结层以上的环流分别以干细胞对流和浮力波为主。当采用1.35作为临界饱和比时，云只表现为强烈的、短暂的、准周期的事件。云从凝结层上方开始向上发展，但强烈的上升气流只存在于云顶周围；它们不会延伸到凝结层的底部。在云事件期间，云层在潜热作用下迅速升温，然后在特定的热强迫作用下缓慢冷却，并逐渐发生过饱和，导致下一次云事件的发生。当凝聚粒子数混合比较大时，不会出现云事件的周期性出现。
Cloud convection of a CO2atmosphere 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-periodic events. Clouds start just above the condensation level and develop upward, but intense updrafts exist only around the cloud top; they do not extend to the bottom of the condensation layer. The cloud layer is rapidly warmed by latent heat during the cloud events, and then the layer is slowly cooled by the specified thermal forcing, and supersaturation gradually develops leading to the next cloud event. The periodic appearance of cloud events does not occur when number mixing ratio of condensed particles is large.