The effect of time steps and time‐scales on parametrization suites
The effect of time steps and time‐scales on parametrization suites
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DOI：
10.1002/qj.1992
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发表时间：
2013
影响因子：
8.9
通讯作者：
D. Williamson
中科院分区：
文献类型：
--
作者：
D. Williamson
本文研究了社区大气模式第4版（CAM4）高分辨率版本中形成的强烈截断尺度风暴问题。这些风暴的特点是极端的垂直运动和强降水。当一些单独的参数化由于受到其公式中假设的时间尺度的限制而不能产生类似大气的状态时，就会出现这个问题；随后的其他无约束参数化以意想不到的方式工作。在CAM4中检查了一个典型的强细胞的湿参数化组件的行为。在T340光谱截断5 min时间步长时，深对流和浅对流参数化不能去除不稳定性和过饱和度，因为它们分别具有1 h和30 min的时间尺度。因此，不受时间尺度限制的预测云-水方案确实消除了过饱和度。潜热的局部释放驱动了非常强烈的垂直运动和水平辐合，这将更多的水蒸气输送到气柱中，从而加剧了问题。介绍了两个简单的模型问题，说明了时间尺度和时间步长不匹配的后果。当时间尺度缩短或时间步长延长时，对流参数化更加活跃，不形成强风暴。版权所有©2012英国皇家气象学会
The problem of intense, truncation‐scale storms that form in high‐resolution versions of the Community Atmosphere Model Version 4 (CAM4) is studied. These storms are characterized by extreme vertical motion and heavy precipitation. This problem arises when some individual parametrizations do not produce an atmospheric‐like state because they are restrained by the time‐scales assumed in their formulation; other unconstrained parametrizations that follow then work in unintended ways. The behaviour of the moist parametrization components is examined in CAM4 for one typical, strong cell. At T340 spectral truncation with a 5 min time step, the deep and shallow convection parametrizations do not remove instabilities and supersaturation because they have time‐scales of 1 h and 30 min, respectively. Then the prognostic cloud‐water scheme, which is not constrained by a time‐scale, does remove supersaturation. That local release of latent heat drives very strong vertical motion and horizontal convergence, which transports even more water vapour into the column, exacerbating the problem. Two simple model problems are introduced that illustrate the ramifications of the time‐scale and time‐step mismatch. When either the time‐scales are shortened or the time step is lengthened, the convection parametrizations are more active and strong storms do not form. Copyright © 2012 Royal Meteorological Society