How large-scale subsidence affects stratocumulus transitions
How large-scale subsidence affects stratocumulus transitions
复制标题
大规模沉降如何影响层积云转变
DOI：
10.5194/acp-16-691-2016
复制
发表时间：
2015
影响因子：
6.3
通讯作者：
A. P. Siebesma
中科院分区：
文献类型：
--
作者：
J. V. D. Dussen;S. Roode;A. P. Siebesma
抽象。一些气候模拟结果表明，哈德利环流可能会在未来的气候减弱，导致随后在亚热带地区的大规模沉降速度的减少。在这项研究中，我们分析了云液态水路径（LWP）的预算大涡模拟（LES）结果的三个理想化层积云过渡的情况下，每一个不同的下沉率。如在以前的研究中所示，减少沉降被发现导致更深的层积云顶部的边界层，增强云顶夹带率和延迟的层积云过渡到浅积云在其赤道平流盛行信风。沉降率降低的影响可概括如下。层积云层的初始加深部分地被增强的太阳辐射吸收所抵消。几小时后，边界层的加深由于卷吸率的增加而加速。由于这是伴随着云底的水汽和热量的湍流通量的变化，在LWP的净变化，由于湍流通量廓线的变化是微不足道的小。
Abstract. Some climate modeling results suggest that the Hadley circulation might weaken in a future climate, causing a subsequent reduction in the large-scale subsidence velocity in the subtropics. In this study we analyze the cloud liquid water path (LWP) budget from large-eddy simulation (LES) results of three idealized stratocumulus transition cases, each with a different subsidence rate. As shown in previous studies a reduced subsidence is found to lead to a deeper stratocumulus-topped boundary layer, an enhanced cloud-top entrainment rate and a delay in the transition of stratocumulus clouds into shallow cumulus clouds during its equatorwards advection by the prevailing trade winds. The effect of a reduction of the subsidence rate can be summarized as follows. The initial deepening of the stratocumulus layer is partly counteracted by an enhanced absorption of solar radiation. After some hours the deepening of the boundary layer is accelerated by an enhancement of the entrainment rate. Because this is accompanied by a change in the cloud-base turbulent fluxes of moisture and heat, the net change in the LWP due to changes in the turbulent flux profiles is negligibly small.