Shamekh S, Muller C, Duvel J-P, D'Andrea F
Laboratoire de Météorologie Dynamique IPSL, École Normale Supérieure, PSL Research University, CNRS Paris France.
J Adv Model Earth Syst. 2020 Nov;12(11):e2020MS002164. doi: 10.1029/2020MS002164. Epub 2020 Nov 3.
This study investigates the feedbacks between an interactive sea surface temperature (SST) and the self-aggregation of deep convective clouds, using a cloud-resolving model in nonrotating radiative-convective equilibrium. The ocean is modeled as one layer slab with a temporally fixed mean but spatially varying temperature. We find that the interactive SST decelerates the aggregation and that the deceleration is larger with a shallower slab, consistent with earlier studies. The surface temperature anomaly in dry regions is positive at first, thus opposing the diverging shallow circulation known to favor self-aggregation, consistent with the slower aggregation. But surprisingly, the driest columns then have a negative SST anomaly, thus strengthening the diverging shallow circulation and favoring aggregation. This diverging circulation out of dry regions is found to be well correlated with the aggregation speed. It can be linked to a positive surface pressure anomaly (PSFC), itself the consequence of SST anomalies and boundary layer radiative cooling. The latter cools and dries the boundary layer, thus increasing PSFC anomalies through virtual effects and hydrostasy. Sensitivity experiments confirm the key role played by boundary layer radiative cooling in determining PSFC anomalies in dry regions, and thus the shallow diverging circulation and the aggregation speed.
本研究利用非旋转辐射对流平衡中的云分辨模型，研究了交互式海表面温度（SST）与深对流云自我聚集之间的反馈。海洋被模拟为一层具有固定时间平均但空间变化温度的平板。我们发现交互式SST减缓了聚集，并且平板越浅减速越大，这与早期研究一致。干旱区域的表面温度异常最初为正，因此与已知有利于自我聚集的发散浅层环流相反，这与较慢的聚集一致。但令人惊讶的是，最干燥的气柱随后出现负SST异常，从而加强了发散浅层环流并有利于聚集。发现这种从干旱区域流出的发散环流与聚集速度密切相关。它可以与正表面压力异常（PSFC）联系起来，而PSFC本身是SST异常和边界层辐射冷却的结果。后者使边界层冷却并干燥，从而通过虚拟效应和流体静力平衡增加PSFC异常。敏感性实验证实了边界层辐射冷却在确定干旱区域PSFC异常方面所起的关键作用，进而证实了其在浅层发散环流和聚集速度方面的关键作用。
