Ali S M Anas, Tandon Neil F
Department of Earth and Space Science and Engineering York University Toronto ON Canada.
Department of Physics University of Toronto Toronto ON Canada.
J Geophys Res Atmos. 2024 Nov 28;129(22):e2023JD040146. doi: 10.1029/2023JD040146. Epub 2024 Nov 23.
A fundamental characteristic of extreme precipitation events (EPEs) is their horizontal scale. This horizontal scale can influence the intensity of an EPE through its effect on the timescale of an EPE as well as its effect on the strength of convective feedbacks. Thus, to have confidence in future projections of extreme precipitation, the horizontal scales of EPEs in global climate models (GCMs) should be evaluated. Analyzing daily output from 27 models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6), including 13 models participating in the High Resolution Model Intercomparison Project (HighResMIP), we computed the horizontal scales of EPEs and extreme ascent for annual maximum EPEs during 1981-2000. We found that the horizontal scales of both EPEs and the associated ascending motion are resolution-dependent: for a factor of seven increase in horizontal resolution, the horizontal scale decreases by a factor of approximately two to five, with higher sensitivity in the tropics than in the midlatitudes. Further analysis in the southern hemisphere midlatitudes reveals that this resolution dependence results from precipitation during the simulated EPEs that is almost entirely resolved rather than parameterized. However, the EPEs are not simply grid box storms, and analysis of the horizontal scales of geopotential anomalies suggests that the planetary-scale dynamics in GCMs is not resolution-dependent. Thus, the dominance of resolved precipitation during EPEs is more likely due to convection on the model grid or formation of strong, poorly resolved fronts, and additional work is needed to explore these possibilities and find a remedy for this resolution dependence.
极端降水事件（EPEs）的一个基本特征是其水平尺度。这种水平尺度可通过对EPEs时间尺度的影响以及对对流反馈强度的影响来影响EPE的强度。因此，为了对未来极端降水的预测有信心，应评估全球气候模型（GCMs）中EPEs的水平尺度。通过分析参与耦合模式比较计划第6阶段（CMIP6）的27个模式的日输出数据，包括参与高分辨率模式比较计划（HighResMIP）的13个模式，我们计算了1981 - 2000年期间年度最大EPEs的EPEs水平尺度和极端上升情况。我们发现，EPEs及其相关上升运动的水平尺度都依赖于分辨率：水平分辨率增加7倍时，水平尺度大约减小2至5倍，热带地区的敏感性高于中纬度地区。在南半球中纬度地区的进一步分析表明，这种分辨率依赖性源于模拟EPEs期间的降水几乎完全是解析的而非参数化的。然而，EPEs并非简单的网格盒风暴，位势异常水平尺度的分析表明GCMs中的行星尺度动力学不依赖于分辨率。因此，EPEs期间解析降水占主导更可能是由于模型网格上的对流或强烈但解析度差的锋面的形成，需要开展更多工作来探索这些可能性并找到解决这种分辨率依赖性的方法。
