文章基本信息

标题：Evaluation of WRF SCM Simulations of Stratocumulus‐Topped Marine and Coastal Boundary Layers and Improvements to Turbulence and Entrainment Parameterizations
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作者：Mohamed S. Ghonima ; Handa Yang ; Chang Ki Kim 等
期刊名称：Journal of Advances in Modeling Earth Systems
电子版ISSN：1942-2466
出版年度：2017
卷号：9
期号：7
页码：2635-2653
DOI：10.1002/2017MS001092
出版社：John Wiley & Sons, Ltd.
摘要：Stratocumulus‐topped boundary layers (STBLs) are notoriously difficult to parameterize in single‐column models due to the strong inversion layer across which entrainment mixing plays an important role in modulating the boundary layer mass, energy, and moisture balances. We compare three different WRF planetary boundary layer (PBL) schemes (Yonsei University, YSU; Asymmetric Convective Model version 2, ACM2; Mellor‐Yamada‐Nakanishi‐Niino, MYNN) against large eddy simulations (LES) to find out that they underestimate entrainment flux in stratocumulus over both ocean and coastal land. Hence, the PBL schemes produce a cooler, moister STBL with higher liquid water content. In order to improve the entrainment parameterization, we propose a modification to the YSU scheme that takes into account the in‐cloud turbulence flux contribution to cloud top entrainment through the formulation of a velocity scale based on the in‐cloud buoyancy flux. A revised top‐down mixing profile is also implemented to model mixing due to turbulence generated by longwave cooling at the cloud top. The modified YSU simulates stronger entrainment flux, resulting in a STBL that matches LES results. Similar modifications were made to ACM2 in addition to implementing explicit entrainment, and while the results also showed good agreement with LES, discretization issues and conflicts with its original design prevent immediate implementation, as the contribution from the modifications and the original scheme are difficult to correctly modulate.
关键词：WRF;stratocumulus;parameterization;turbulence;entrainment;coastal