Champion Adrian J, Blenkinsop Stephen, Li Xiao-Feng, Fowler Hayley J
Department of Meteorology University of Reading Reading UK.
College of Engineering, Mathematical and Physical Sciences University of Exeter Exeter UK.
J Geophys Res Atmos. 2019 Apr 27;124(8):4477-4489. doi: 10.1029/2018JD029664. Epub 2019 Apr 29.
The synoptic-scale meteorological conditions leading up to the 30 most extreme subdaily summer rain events for two regions of the United Kingdom (northwest and southeast) were examined for the period 1979-2013. Using a recently available, quality controlled, national hourly rain gauge data set, we were able to identify extreme 3-hr rainfall accumulations that may be indicative of flash flooding. Composites of the state of the atmosphere leading up to these dates were produced to investigate synoptic-scale processes, thus potentially allowing for them to be identified in coarse resolution reanalyses and in climate models. The results show that the two regions have different dominant synoptic-scale conditions leading to extreme 3-hr rainfall, which is thought to be related to the type of rainfall typically experienced in each region. In particular, positive anomalies in mean sea level pressure and the geopotential height at 200 hPa over the United Kingdom are associated with extreme rainfall in the northwest, where the position of the westerly jet is also important. For the southeast, no clear anomalous synoptic-scale conditions could be identified; however, localized moisture sources and unstable air masses were observed in association with extremes. These results indicate the importance of better understanding of both synoptic-scale and thermodynamic drivers of short-duration extreme rainfall, with potential implications in forecasting and flood warning, as well as for understanding the representation of key processes by regional climate models.
对1979 - 2013年期间英国两个地区（西北部和东南部）30次最极端的夏季次日常降雨事件之前的天气尺度气象条件进行了研究。利用最近可得的、经过质量控制的全国每小时雨量计数据集，我们能够识别出可能预示着山洪暴发的极端3小时降雨累积量。制作了这些日期之前的大气状态合成图，以研究天气尺度过程，从而有可能在粗分辨率再分析和气候模型中识别这些过程。结果表明，两个地区导致极端3小时降雨的主导天气尺度条件不同，这被认为与每个地区通常经历的降雨类型有关。特别是，英国上空平均海平面气压和200百帕等压面位势高度的正异常与西北部的极端降雨有关，西风急流的位置在那里也很重要。对于东南部，无法确定明显的异常天气尺度条件；然而，观察到局部水汽源和不稳定气团与极端降雨有关。这些结果表明，更好地理解短期极端降雨的天气尺度和热力驱动因素非常重要，这对预报和洪水预警以及理解区域气候模型中关键过程的表现都有潜在影响。
