Boundary Layer Dynamics after Rain Fronts: High-Resolution Reconstruction and Model Validation using ground- and drone-based Measurements

Abstract. Understanding atmospheric processes enables enhancing weather forecasts and models. Research in polluted areas showed that severe rain fronts influence pollutant distribution and chemical processes in the planetary boundary layer, while studies at continental rural mid-latitude sites emphasized stratification's impact on pollutants, but neglected the influence of rain fronts. This study connects meteorological and chemical boundary layer 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. Findings reveal that delayed nocturnal boundary layer breakup and poor vertical mixing result in weakly oxidized organic aerosol and reduced secondary aerosol formation near ground. Suppressed vertical mixing in the morning delays daytime chemical processes. A temporary reduction of O₃ after rain was observed, likely due to depletion from reactions 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. In-situ measurements indicate that cold pool dynamics enhance subsequent convective development. 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.