Planetary boundary layer dynamics over a coastal desert city

Doha, Qatar, is a dry, arid region that has undergone extensive urbanization in recent periods. As a result, the region is experiencing strong urban heat island effects, in addition to dust storms, and heat wave conditions. The Planetary boundary layer (PBL) is a crucial variable in a better understanding of local weather and air quality. Measurement of PBL is challenging due to its complex vertical structure and significant variability over time and space. In this study, the Vaisala CL51 ceilometer is used to investigate the distribution and variability of PBL height over Doha. Continuous observations of ceilometer data throughout the year 2023 were collected and analyzed using the BL-view software. The deepest PBL is observed during the dry summer season (1400m), followed by the winter (1250m) and humid summer season (1100m). This variability in PBL height highlights the critical role of local weather conditions in shaping the PBL structure over thermodynamically active regions like Doha. Further analysis is conducted on selected cases, which show significant deviation from the expected PBL height. The diurnal profiles exhibited significant daily variations, with some days showing well-developed PBLs (maximum height ~3500m), shallow PBLs (maximum height ~100m), and days with no significant diurnal PBL variation. Surprisingly, on some days in the dry summer season, the analysis reveals the crucial role played by the mechanical production of turbulence in the structure of PBL over a thermodynamically active region like Doha. The depth and diurnal distribution of the PBL height show sensitivity towards the prevailing wind pattern over the region. The sensitivity of PBL on the wind pattern, drag coefficient, and flux values implies the importance of urban planning over such regions to improve human thermal comfort.