Diurnal Modulation of Moist Processes in Summertime Droughts and Floods over the Central United States

这个研究小组将评估美国中部夏季降雨及其日变化的各种过程的相对影响和综合影响。 日变化对中纬度夏季水文循环有重要影响，夜间低空急流和中尺度对流系统起着重要作用。 本研究将探讨三个假设：（1）大尺度的日变化是逐年变化的，因此，在洪（旱）年，暴雨诱导过程的峰值出现在夜间（白天）。 (2)在洪水年，贡献过程的相位一起产生增强的降水和更强的夜间最大值，而在干旱年的组件是日相。 (3)洪水年的大尺度强迫有利于对流的组织和高档增长，从而将降水峰值转移到深夜/清晨。主要研究人员将采用观察分析和数值模拟方法来检验假设。 数值研究将用于分离和过滤空间和时间域的扰动，以便在区域气候模拟中系统地研究其影响。 这项研究将涵盖中西部正常、干旱和洪水年份的选择。这项研究是NSF的水和能源：大气，植被和地球相互作用（WEAVE）工作的一部分。

This team of investigators will evaluate both the relative and combined effects of various processes contributing to summer rainfall and its diurnal variability in the central United States. Diurnal variation has important effects on the summer hydrologic cycle in the mid-latitudes with the nocturnal low-level jet and mesoscale convective systems playing significant roles. Three hypotheses will be examined: (1) The large-scale diurnal variation changes from year to year such that rainfall-inducing processes peak during the nighttime (daytime) in flood (drought) years. (2) During flood years, the contributing processes phase together to produce enhanced precipitation and a stronger nocturnal maximum, while in drought years the components are out of diurnal phase. (3) Large-scale forcing in flood years favors organization and upscale growth of convection, which shifts peak precipitation to late night/early morning. The principal investigators will employ both observational analysis and numerical modeling approaches to examine the hypotheses. The numerical studies will be used to isolate and filter perturbations in both the spatial and temporal domains so that their influences can be systematically examined in regional climate simulations. The study will cover a selection of normal, drought, and flood years in the Midwest. This research is supported as part of NSF's Water and Energy: Atmospheric, Vegetative, and Earth Interactions (WEAVE) effort.