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首页> 外文期刊>Journal of the Atmospheric Sciences >Convective Momentum Transport in a Simple Multicloud Model for Organized Convection
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Convective Momentum Transport in a Simple Multicloud Model for Organized Convection

机译：用于组织对流的简单多云模型中的对流动量传输

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Convective momentum transport (CMT) is the process of vertical transport of horizontal momentum by convection onto the environmental flow. The significance of CMT from mesoscale to synoptic- and planetary-scale organized cumulus convection has been established by various theoretical and observational studies. A new strategy mimicking the effect of unresolved mesoscale circulation based on the weak temperature gradient (WTG) approximation with a Gaussian profile to redistribute the heating due to parameterized cumulus convection at the subgrid scale is adopted here to construct a CMT parameterization for general circulation models (GCMs). Two main regimes of CMT are considered: an upscale squall-line regime and a downscale non-squall-line regime. An exponential probability distribution is used to select which of these two effects is active, conditional on the state of the large-scale shear. The shear itself is used as a measure of the persistence of mesoscale organized circulation due to the presence or not of tilted deep convective heating with lagged stratiform anvils. The CMT model is tested in the simple case of the multicloud model of Khouider and Majda, used here as a toy GCM. Numerical simulations are performed here for the simple case without rotation, in a parameter regime where the multicloud model exhibits packets of convectively coupled gravity waves moving in one direction, at 17 m s~(-1), and planetary-scale wave envelopes moving in the opposite direction, at 4-6 m s~(-1), reminiscent of the Madden-Julian oscillation (MJO) and the associated embedded synoptic-scale superclusters. The results herein show that the inclusion of CMT intensifies both the synoptic-scale convectively coupled waves and the manifestation of planetary-scale waves in the multicloud model. This provides evidence that the present CMT model captures the essence of the physical mechanism through which kinetic energy is transferred from the subgrid-scale mesoscale circulation to the large-scale/resolved motion. Sensitivity simulations showed that two key parameters for the CMT parameterization are the relative strength of the parameterized stratiform anvils and the dimensional threshold used in the exponential distribution for the cumulus friction and the upscale CMT forcing resulting from organized subgrid mesoscale circulation.
机译：对流动量传输（CMT）是通过对流到环境流上的水平动量的垂直传输过程。从各种中尺度到天气尺度和行星尺度的有组织积云对流，CMT的重要性已经通过各种理论和观察研究得到了证实。本文采用一种新的策略来模拟未解决的中尺度环流的影响，该策略基于具有高斯分布的弱温度梯度（WTG）近似值来重新分配亚网格尺度上因参数化积云对流而产生的热量，从而为一般环流模型构建CMT参数化（ GCM）。考虑了CMT的两个主要制度：高档线政权和高档非non线政权。使用指数概率分布来选择这两种效应中的哪一种是有效的，其条件是大规模剪切的状态。由于存在或不存在带有滞后的层状铁砧的倾斜深对流加热，剪切机本身可用于衡量中尺度有组织循环的持续性。在Khouider和Majda的多云模型的简单情况下对CMT模型进行了测试，此处用作玩具GCM。在不带旋转的简单情况下，在此参数模型中进行了数值模拟，其中多云模型展示了以17 ms〜（-1）的方向对流耦合的对流耦合重力波包，并且以方向相反，在4-6 ms〜（-1）时，让人联想到Madden-Julian振荡（MJO）和相关的嵌入天气尺度超团簇。本文的结果表明，在多云模型中，CMT的加入既增强了天气尺度对流耦合波，又增强了行星尺度波的表现。这提供了证据，表明当前的CMT模型掌握了物理机制的本质，动能通过该机制将动能从亚网格尺度的中尺度循环转移到了大规模的/分解的运动。敏感性仿真显示，CMT参数化的两个关键参数是参数化层状砧的相对强度，积云摩擦指数分布中使用的尺寸阈值以及由有组织的亚网格中尺度环流引起的高档CMT强迫。

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