The Dry-Entropy Budget of a Moist Atmosphere
The Dry-Entropy Budget of a Moist Atmosphere
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DOI：
10.1175/2008jas2679.1
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发表时间：
2008-12
影响因子：
3.1
通讯作者：
D. Romps
中科院分区：
文献类型：
--
作者：
D. Romps
熵收支一直是湿大气做功或耗散理论的流行起点。对于干燥的大气，熵收支提供了一个理论的耗散方面的强制非绝热热源。对于湿大气，量化不可逆湿过程或凝结温度的值的困难，迄今为止，阻碍了建立耗散理论的努力。考虑到这种复杂性，这里的目标之一是研究干熵预算的预测能力（即，热容乘以位温的对数）。为此目的，干熵预算来自现实的热容量和固体水相，功能，从一些以前的研究大气熵缺席的大气。结果表明，干熵收支可以解释为6个过程的源和汇的总和，这些过程按大小顺序为：辐射冷却、凝结加热、地面感热、风生摩擦耗散、水的抬升和从融化线到对流层上部的热量输送。这幅图为潮湿大气发动机的低效率提供了另一种解释。数值模拟提出了一个新的云解析模式，Das Atmospharische Modell，这是为了节省能量和关闭干熵预算。模拟和不亚网格扩散的热量和水进行了比较，研究亚网格参数化的干熵预算的条款的影响。数值结果表明，风产生的耗散，似乎是有效的海表面温度和平均风的变化，一个特别简单的参数化。干熵收支还指出了强迫和参数化的各种变化，这些变化可能会增加或减少风产生的耗散。
The entropy budget has been a popular starting point for theories of the work, or dissipation, performed by moist atmospheres. For a dry atmosphere, the entropy budget provides a theory for the dissipation in terms of the imposed diabatic heat sources. For a moist atmosphere, the difficulties in quantifying irreversible moist processes or the value of the condensation temperature have so far frustrated efforts to construct a theory of dissipation. With this complication in mind, one of the goals here is to investigate the predictive power of the budget of dry entropy (i.e., the heat capacity times the logarithm of potential temperature). Toward this end, the dry-entropy budget is derived for an atmosphere with realistic heat capacities and a solid-water phase, features that were absent from some previous studies of atmospheric entropy. It is shown that the dry-entropy budget may be interpreted as the sum of sources and sinks from six processes, which are, in order of decreasing magnitude, radiative cooling, condensation heating, sensible heating at the surface, wind-generated frictional dissipation, lifting of water, and transport of heat from the melting line to the upper troposphere. This picture leads to an alternative explanation for the low efficiency of the moist atmospheric engine. Numerical simulations are presented from a new cloud-resolving model, Das Atmospharische Modell, which was designed to conserve energy and close the dry-entropy budget. Simulations with and without subgrid diffusion of heat and water are compared to investigate the impact of subgrid parameterizations on the terms in the dry-entropy budget. The numerical results suggest a particularly simple parameterization of wind-generated dissipation that appears to be valid for changes in sea surface temperature and mean wind. The dry-entropy budget also points to various changes in forcings and parameterizations that could be expected to increase or decrease the wind-generated dissipation.