Comparative Analysis of Planetary Boundary Layer Heights During the BELLA CIAO Measurement Campaign in Italy

Highlights: What are the main findings? The MIPA algorithm applied to ground-based lidar measurements better captures daytime PBLH evolution, particularly during convective growth and evening transitions, while ERA5 provides the most accurate nighttime PBLH estimates. A combined approach using MIPA for daytime and ERA5 for nighttime significantly improves overall performance of PBLH retrievals, achieving the highest agreement with radiosonde observations among all tested methods. What are the implications of the main findings? Integrating ground-based lidar retrievals with atmospheric reanalysis products enables more reliable monitoring of the full diurnal PBLH cycle with stand-alone lidars. The combined MIPA–ERA5 method offers a robust framework for operational boundary layer monitoring, supporting air quality assessment and public health applications. This study presents an intercomparison of planetary boundary layer height (PBLH) estimates derived from three distinct approaches: the Morphological Image Processing Approach (MIPA) algorithm applied to ground-based lidar measurements, European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis 5th Generation (ERA5) and Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2) reanalysis model outputs, and radiosonde (RS) observations, this latter being taken as reference. The intercomparison was conducted during three measurement episodes, encompassing a total of 153 h (6 days), as part of the Boundary Layer Extensive Campaign with muLti-instrumentaL Analysis (BELLA), carried out in spring and early summer 2024 at the CNR-IMAA Atmospheric Observatory (CIAO) in southern Italy (40.60N, 15.72E). The study provides insights into the performance and reliability of these PBLH estimation approaches under diverse atmospheric scenarios. Visual and statistical analyses of selected case studies indicate that MIPA often tracked the aerosol layering structure and diurnal PBLH evolution more closely than ERA5 and MERRA-2, particularly during convective growth and evening transitions. On the other hand, it is found that ERA5 provides more accurate estimates of the nighttime PBLH, where MIPA shows poor nighttime estimation capabilities. Quantitative comparison against radiosonde data reveals that MIPA reaches a weighted root mean square error ((Formula presented.)) of (Formula presented.) m with a coefficient of determination ((Formula presented.)) of (Formula presented.), while ERA5 shows an (Formula presented.) of (Formula presented.) m and an (Formula presented.) of (Formula presented.) ; and MERRA-2 shows an (Formula presented.) of (Formula presented.) m and an (Formula presented.) of (Formula presented.). By combining MIPA daytime and ERA5 nighttime PBLH, the overall results are improved, obtaining an (Formula presented.) and an (Formula presented.) of (Formula presented.) m. This intercomparison highlights the strengths and limitations of each method and demonstrates the benefits of combining complementary PBLH retrieval techniques. The findings contribute to refining boundary layer monitoring methodologies and provide guidance for operational atmospheric observation networks.