Large‐eddy simulation of subtropical cloud‐topped boundary layers: 1. A forcing framework with closed surface energy balance
Large‐eddy simulation of subtropical cloud‐topped boundary layers: 1. A forcing framework with closed surface energy balance
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副热带云顶边界层大涡模拟：1. 封闭地表能量平衡的强迫框架
DOI：
10.1002/2016ms000655
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发表时间：
2016
影响因子：
6.8
通讯作者：
K. Pressel
中科院分区：
文献类型：
--
作者：
Zhihong Tan;T. Schneider;J. Teixeira;K. Pressel
云的大涡模拟（LES）有可能解决气候动力学中的一个核心问题，即亚热带海洋边界层（MBL）云如何对全球变暖做出响应。然而，在有限区域的LES区域中，大尺度过程需要被规定或以参数化方式表示。重要的是，大尺度过程的表示要满足诸如封闭能量平衡等约束条件，并且在气候变化下是可实现的。例如，具有固定海面温度的LES通常无法实现表面能量平衡的闭合，这可能导致虚假的表面通量以及云对气候变化的响应。在此，提出了一个用于强迫亚热带MBL云的LES的框架，该框架通过将大气LES与具有取决于辐射通量以及表面感热和潜热通量的海面温度（SST）的海洋混合层耦合，来实现封闭的表面能量平衡。在这个框架内成功地模拟了多种亚热带MBL云型（层积云、积云以及积云上方的层积云）。然而，与具有固定SST的传统框架不同，云量和SST之间出现了反馈，当强迫参数变化时，这可能导致云型之间的突然转变（例如，从层积云到积云）。这些模拟验证了这个用于MBL云研究的框架，并确立了它在研究云如何对气候变化做出响应方面的有用性。
Large‐eddy simulation (LES) of clouds has the potential to resolve a central question in climate dynamics, namely, how subtropical marine boundary layer (MBL) clouds respond to global warming. However, large‐scale processes need to be prescribed or represented parameterically in the limited‐area LES domains. It is important that the representation of large‐scale processes satisfies constraints such as a closed energy balance in a manner that is realizable under climate change. For example, LES with fixed sea surface temperatures usually do not close the surface energy balance, potentially leading to spurious surface fluxes and cloud responses to climate change. Here a framework of forcing LES of subtropical MBL clouds is presented that enforces a closed surface energy balance by coupling atmospheric LES to an ocean mixed layer with a sea surface temperature (SST) that depends on radiative fluxes and sensible and latent heat fluxes at the surface. A variety of subtropical MBL cloud regimes (stratocumulus, cumulus, and stratocumulus over cumulus) are simulated successfully within this framework. However, unlike in conventional frameworks with fixed SST, feedbacks between cloud cover and SST arise, which can lead to sudden transitions between cloud regimes (e.g., stratocumulus to cumulus) as forcing parameters are varied. The simulations validate this framework for studies of MBL clouds and establish its usefulness for studies of how the clouds respond to climate change.