Daily maps of Boundary Layer Height combining radiosonde, satellite, and reanalysis over Europe

Abstract. The height of the planetary boundary layer directly influences local and regional climatic phenomena, making its study and estimation of vital importance for environmental sciences. The main objective of this work was to create a gridded map of planetary boundary layer height across the European continent, with a spatial resolution of 25 km and monthly mean values at two synoptic hours (12:00 and 00:00 UTC). We implemented the regression kriging method by combining various data sources, including observations, climatic and topographic variables, and reanalysis data (ERA5), and different regression methods (linear, random forest, and gradient boosting) for the 2010–2020 period. In both UTC hours, combining reanalysis and topographic covariates with random forest regression provided the best performance. Then, we compared our seasonal predictions with reanalysis data and found a consistently higher spatio-temporal accuracy than that of the ERA5 reanalysis. For example, at 12:00 UTC, spatial variability in winter showed RMSE values ≤ 100 m, compared with ≥ 200 m for ERA5, while temporal variability in summer reached RMSE values ≤ 250 m, versus ≥ 300 m for ERA5. At 00:00 UTC, spatial variability in autumn achieved RMSE values ≤ 36 m, whereas ERA5 exhibited RMSE values ≥ 130 m.

The methodology was applied to a case study over Germany at a daily resolution. We obtained an accurate representation of boundary layer height, which was consistent with the variations in weather conditions. Results were notably better at 12:00 than at 00:00 UTC, mainly due to the limited number of available stations and the associated difficulty in resolving the stable boundary layer at night. Overall, this study represents a promising first step towards the incorporation of this type of data in atmospheric models with the aim of reducing the bias in boundary layer height simulation.