Jensen Gorm G, Fiévet Romain, Haerter Jan O
Niels Bohr Institute Copenhagen University Copenhagen Denmark.
Complexity and Climate Leibniz Centre for Tropical Marine Research Bremen Germany.
J Adv Model Earth Syst. 2022 May;14(5):e2021MS002923. doi: 10.1029/2021MS002923. Epub 2022 May 23.
Clustering of tropical thunderstorms constitutes an important climate feedback because it influences the radiative balance. Convective self-aggregation (CSA) is a profound modeling paradigm for explaining the clustering of tropical oceanic thunderstorms. However, CSA is hampered in the realistic limit of fine model resolution when cold pools-dense air masses beneath thunderstorm clouds-are well-resolved. Studies on CSA usually assume the surface temperature to be constant, despite realistic surface temperatures varying significantly between night and day. Here we mimic the diurnal cycle in cloud-resolving numerical experiments by prescribing a surface temperature oscillation. Our simulations show that the diurnal cycle enables CSA at fine resolutions, and that the process is even accelerated by finer resolutions. We attribute these findings to vigorous combined cold pools emerging in symbiosis with mesoscale convective systems. Such cold pools suppress buoyancy in extended regions (∼100 km) and enable the formation of persistent dry patches. Our findings help clarify how the tropical cloud field forms sustained clusters under the diurnal forcing and may have implications for the origin of extreme thunderstorm rainfall and tropical cyclones.
热带雷暴的聚集构成了一种重要的气候反馈，因为它会影响辐射平衡。对流自聚集（CSA）是用于解释热带海洋雷暴聚集的一种深刻的建模范式。然而，当冷池（雷暴云下方的密集气团）得到很好的解析时，CSA在精细模型分辨率的现实限制中会受到阻碍。关于CSA的研究通常假定表面温度是恒定的，尽管实际的表面温度在白天和夜晚之间有显著变化。在这里，我们通过规定表面温度振荡在云解析数值实验中模拟昼夜循环。我们的模拟表明，昼夜循环能够在精细分辨率下实现CSA，并且该过程甚至会因更高的分辨率而加速。我们将这些发现归因于与中尺度对流系统共生出现的强烈组合冷池。这种冷池在扩展区域（约100公里）抑制浮力，并使持续干燥斑块得以形成。我们的发现有助于阐明热带云场在昼夜强迫下如何形成持续的集群，并且可能对极端雷暴降雨和热带气旋的起源有影响。
