A Comparative Study of Long‐Term Variability of Urban and Suburban Planetary Boundary Layer Heights Using Ceilometers and the HRRR Model

Abstract

An adaptive algorithm has been developed using ground‐based high‐resolution aerosol backscatter profiles from the Vaisala CL61 ceilometer to retrieve planetary boundary layer height (PBLH). Datasets spanning more than 3 years (2022–2025) from the U.S. National Capital Region (NCR) were comprehensively analyzed. We focused on examining the PBL dynamics representing urban and suburban environments in the National Capital Region. Our findings confirm that the daytime PBLH in both environments follows a typical solar‐driven seasonal cycle. However, the nocturnal boundary layer (NBL) from both sites showed more complex behavior. Although the urban heat island (UHI) related storage may influence nighttime stability, the observed urban‐suburban contrast could not be explained by the UHI effects alone. The suburban site frequently showed elevated nighttime PBLH, suggesting an additional role of mechanical turbulence and land‐atmosphere coupling. To understand the underlying mechanism of this behavior, we analyzed PBL development, particularly after precipitation. Results suggest that following precipitation, PBLH was elevated in the suburban environment. Mean suburban nighttime PBLH was lower 4–5 days after rainfall than in the earlier post‐rainfall intervals, although the change was not monotonic. These patterns suggest a possible influence of land‐surface conditions, but the contributions of soil moisture and evapotranspiration remain uncertain. It appears that soil moisture capacity relative to precipitation may play an important role in the evolution of suburban PBLH. Furthermore, the High‐Resolution Rapid Refresh (HRRR) model was used to compare with observational PBLH and evaluate any systematic biases in the model. Results suggested that the model tends to overestimate PBLHs under convective conditions and significantly underestimate them under stable nocturnal conditions. ERA5 reanalysis latent heat flux data from 2022 to 2025 were further analyzed to investigate the potential role of surface energy exchange in explaining the consistently higher PBLHs observed at the suburban site. The results indicate that differences in energy exchange between urban and suburban environments may contribute to the observed site‐dependent variability in PBLH. Results from this study also demonstrate that the newly developed adaptive algorithm with the CL61 ceilometer may be used for long‐term PBL monitoring and to further fine‐tune PBL parameterizations in high‐resolution meteorological models.