Large‐eddy simulation of subtropical cloud‐topped boundary layers: 2. Cloud response to climate change
Large‐eddy simulation of subtropical cloud‐topped boundary layers: 2. Cloud response to climate change
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副热带云顶边界层大涡模拟：2.云对气候变化的响应
DOI：
10.1002/2016ms000804
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发表时间：
2017
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
使用大涡模拟（LES）研究了亚热带海洋边界层（MBL）云对变暖的响应，其中CO2浓度升高了2-16倍。在LES耦合到一个板状海洋与相互作用的海表温度（SST），表面潜热通量（LHF）的约束下的表面能量平衡，只有温和地加强变暖。因此，在较温暖的气候中，MBL比相应的固定SST LES更浅，其中LHF过度加强，MBL通常加深。推断短波（SW）云反馈与封闭的能量平衡是弱阳性积云。对于层积云来说，它是更强的正值，其大小随着变暖而增加。层积云通常在升温6 K至9 K以上，或CO2浓度增加4至8倍以上时破裂。这是因为云顶长波（LW）冷却驱动的MBL混合随着自由对流层LW不透明度的增加而减弱。层积云的破裂触发了SST的突然和大的增加和MBL加深，这在固定SST的实验中是不会发生的。在变暖的情况下，西南云的辐射效应一般减弱，而对流层低层稳定度增加，这与目前气候中的经验关系相反。MBL更深，如果大规模沉降随着气候变暖而减少，则层积云会持续到温暖的气候。交互式SST和固定SST的实验之间的对比突出了一个封闭的表面能量平衡的重要性，获得可实现的MBL云变暖的反应。
How subtropical marine boundary layer (MBL) clouds respond to warming is investigated using large‐eddy simulations (LES) of a wide range of warmer climates, with CO2 concentrations elevated by factors 2–16. In LES coupled to a slab ocean with interactive sea surface temperatures (SST), the surface latent heat flux (LHF) is constrained by the surface energy balance and only strengthens modestly under warming. Consequently, the MBL in warmer climates is shallower than in corresponding fixed‐SST LES, in which LHF strengthens excessively and the MBL typically deepens. The inferred shortwave (SW) cloud feedback with a closed energy balance is weakly positive for cumulus clouds. It is more strongly positive for stratocumulus clouds, with a magnitude that increases with warming. Stratocumulus clouds generally break up above 6 K to 9 K warming, or above a four to eightfold increase in CO2 concentrations. This occurs because the MBL mixing driven by cloud‐top longwave (LW) cooling weakens as the LW opacity of the free troposphere increases. The stratocumulus breakup triggers an abrupt and large SST increase and MBL deepening, which cannot occur in fixed‐SST experiments. SW cloud radiative effects generally weaken while the lower‐tropospheric stability increases under warming—the reverse of their empirical relation in the present climate. The MBL is deeper and stratocumulus persists into warmer climates if large‐scale subsidence decreases as the climate warms. The contrasts between experiments with interactive SST and fixed SST highlight the importance of a closed surface energy balance for obtaining realizable responses of MBL clouds to warming.