Lochbihler Kai, Lenderink Geert, Siebesma A Pier
The Royal Netherlands Meteorological Institute (KNMI) De Bilt The Netherlands.
Delft University of Technology Delft The Netherlands.
J Adv Model Earth Syst. 2021 Feb;13(2):e2020MS002306. doi: 10.1029/2020MS002306. Epub 2021 Feb 23.
There is increasing evidence that local rainfall extremes can increase with warming at a higher rate than expected from the Clausius-Clapeyron (CC) relation. The exact mechanisms behind this super-CC scaling phenomenon are still unsolved. Recent studies highlight invigorated local dynamics as a contributor to enhanced precipitation rates with warming. Here, cold pools play an important role in the process of organization and deepening of convective clouds. Another known effect of cold pools is the amplification of low-level moisture variability. Yet, how these processes respond to climatic warming and how they relate to enhanced precipitation rates remains largely unanswered. Unlike other studies which use rather simple approaches mimicking climate change, we present a much more comprehensive set of experiments using a high-resolution large eddy simulation (LES) model. We use an idealized but realistically forced case setup, representative for conditions with extreme summer precipitation in midlatitudes. Based on that, we examine how a warmer atmosphere under the assumption of constant and varying relative humidity, lapse rate changes and enhanced large-scale dynamics influence precipitation rates, cold pool dynamics, and the low-level moisture field. Warmer conditions generally lead to larger and more intense events, accompanied by enhanced cold pool dynamics and a concurring moisture accumulation in confined regions. The latter are known as preferred locations for new convective events. Our results show that cold pool dynamics play an increasingly important role in shaping the response of local precipitation extremes to global warming, providing a potential mechanism for super-CC behavior as subject for future research.
越来越多的证据表明，局部极端降雨随变暖的增加速率可能高于克劳修斯 - 克拉珀龙（CC）关系预期的速率。这种超CC尺度现象背后的确切机制仍未得到解决。最近的研究强调，局部动力学的增强是变暖导致降水率增加的一个因素。在这里，冷池在对流云的组织和加深过程中起着重要作用。冷池的另一个已知效应是放大低层湿度变率。然而，这些过程如何响应气候变暖以及它们如何与增强的降水率相关，在很大程度上仍未得到解答。与其他使用相当简单的方法模拟气候变化的研究不同，我们使用高分辨率大涡模拟（LES）模型进行了一套更全面的实验。我们使用了一个理想化但实际强迫的案例设置，代表了中纬度地区极端夏季降水的条件。在此基础上，我们研究了在相对湿度恒定和变化、 lapse率变化以及增强的大尺度动力学假设下，更温暖的大气如何影响降水率、冷池动力学和低层湿度场。更温暖的条件通常会导致更大、更强烈的事件，同时伴随着冷池动力学的增强和在受限区域内同时出现的水分积累。后者被认为是新对流事件的优选位置。我们的结果表明，冷池动力学在塑造局部极端降水对全球变暖的响应方面发挥着越来越重要的作用，为未来研究提供了超CC行为的潜在机制。
