Single‐Column Model Simulations of Subtropical Marine Boundary‐Layer Cloud Transitions Under Weakening Inversions
Single‐Column Model Simulations of Subtropical Marine Boundary‐Layer Cloud Transitions Under Weakening Inversions
复制标题
弱逆温条件下副热带海洋边界层云转变的单柱模型模拟
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发表时间：
2017
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通讯作者：
Kuan Xu
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作者：
R. Neggers;A. Ackerman;W. Angevine;E. Bazile;I. Beau;P. Blossey;I. Boutle;C. D. Bruijn;A. Cheng;J. V. D. Dussen;J. Fletcher;S. D. Gesso;A. Jam;H. Kawai;S. Cheedela;V. Larson;M. Lefebvre;A. Lock;N. R. Meyer;S. Roode;WC de Rooy;I. Sandu;H. Xiao;Kuan Xu
介绍了GASS/EUCLIPSE单柱模式对副热带海洋低层云转换的比较研究结果。一个中心目标是建立最先进的边界层方案的性能，为天气和气候模式为这种云制度，使用大涡模拟相同的场景作为参考。一个新奇的是，比较涵盖四个不同的情况下，而不是一个，以扩大覆盖的参数空间。三个案例位于东北太平洋，一个案例反映了东北大西洋的情况。考虑一组反映过渡过程关键方面的变量，利用简单的指标来建立模型性能。使用这种方法，一些长期存在的问题，在低级别的云表示。关于云量、云量的垂直结构以及对辐射传输的相关影响，各模型之间存在着相当大的差异。这些偏差的符号和幅度在每个案例中都有所不同，这取决于过渡的进展程度。在云分裂后，集合中值表现出众所周知的“太少太亮”问题。边界层加深速率及其解耦状态都被低估了，而薄盖云层的表示由于缺乏垂直分辨率而显得复杂。令人鼓舞的是，一些模式成功地代表了一整套变量，特别是垂直结构和云层的日变化。一个有趣的结果是，模型集合的中位数表现最好，激发了一种新的方法在次网格参数化。
Results are presented of the GASS/EUCLIPSE single‐column model intercomparison study on the subtropical marine low‐level cloud transition. A central goal is to establish the performance of state‐of‐the‐art boundary‐layer schemes for weather and climate models for this cloud regime, using large‐eddy simulations of the same scenes as a reference. A novelty is that the comparison covers four different cases instead of one, in order to broaden the covered parameter space. Three cases are situated in the North‐Eastern Pacific, while one reflects conditions in the North‐Eastern Atlantic. A set of variables is considered that reflects key aspects of the transition process, making use of simple metrics to establish the model performance. Using this method, some longstanding problems in low‐level cloud representation are identified. Considerable spread exists among models concerning the cloud amount, its vertical structure, and the associated impact on radiative transfer. The sign and amplitude of these biases differ somewhat per case, depending on how far the transition has progressed. After cloud breakup the ensemble median exhibits the well‐known “too few too bright” problem. The boundary‐layer deepening rate and its state of decoupling are both underestimated, while the representation of the thin capping cloud layer appears complicated by a lack of vertical resolution. Encouragingly, some models are successful in representing the full set of variables, in particular, the vertical structure and diurnal cycle of the cloud layer in transition. An intriguing result is that the median of the model ensemble performs best, inspiring a new approach in subgrid parameterization.