The 50-Year Evolution of the Planetary Boundary Layer in the Southern Part of Romania: Comparison Between the Determinations by the Stull Method and the Reanalysis Data from ERA5

The Planetary Boundary Layer (PBL) remains a popular research topic, given its funda-mental role in the exchange of energy between the surface and the atmosphere. Under-standing the PBL's mechanisms can improve weather forecasting and climate and air quality modelling. This paper presents a PBL climatology based on 50 years of observa-tions (1973–2023) from the Bucharest Băneasa radio sounding station in Romania (inter-national identifier 15420). The Stull method was used to calculate the PBL height, which was extracted from the sounding at the Bucharest Băneasa observation point and consid-ers virtual potential temperature (θ_v). This incorporates the effect of humidity on air density. The analysis of climatological seasons (DJF, MAM, JJA and SON) based on PBL height series determined at 00 and 12 UTC using RAOB software revealed that the mixed layer height, as calculated by the Stull method, mainly captures the nocturnal Stable Boundary Layer (SBL) at 00 UTC and highlights the mixed layer (ML) at 12 UTC. ERA5 reanalysis data were also used in parallel.