Boundary layer dynamics after rain fronts: high-resolution reconstruction and model validation using ground- and drone-based measurements

Abstract

Understanding atmospheric processes is essential for improving weather forecasts and models, but in continental regions the effects of dynamical mixing and frontal events on the chemical composition of the planetary boundary layer (PBL) remain poorly characterized. This study connects meteorological and chemical PBL processes during summer rain in Central and Southern rural Germany, focusing on two events: a warm front in a high-pressure system and a cold front following a convergence line. By combining near-hourly drone-based vertical profiles of the lowest 500 m, continuous ground-based observations, and ICON forecast model data, a detailed assessment of tropospheric dynamics for both events was achieved showing that a weak PBL inhibited vertical mixing and resulted in poorly oxidized organic aerosol near ground. Suppressed vertical mixing in the morning delays daytime chemical processes. A temporary post-rain O3 depletion was linked to possible reaction with surface emissions, until mixing restored vertical homogeneity. The ICON model accurately predicted the mixing layer height under stable conditions, but underestimated it during cold pool formation with rain showers and thunderstorms. The in-situ measurements indicate the occurrence of cold pools, subsequent convective activity and disturbances of the PBL dynamics. Analyzing these events helps to reduce uncertainty of model simulations and enhances the PBL parameterization. These findings enhance the understanding of air mass exchange and precipitation's effects on the lower rural troposphere as well as frontal weather scenarios and atmospheric composition changes, linking local experimental and model forecast observations to larger-scale synoptic situations.