Quantification of urban region planetary boundary layer characteristics over edge of outflow of IGP and inflow of Bay of Bengal

The Atmospheric Boundary Layer (ABL) structure plays a crucial role in meteorology and pollution studies in the urban regions. To gain a comprehensive understanding of variability of ABL, its characteristics and factors influencing the ABL, we utilized 3 years of measurements from the Väisälä CL51 ceilometer located at the Kolkata Camp Observatory of NARL (KCON) at the Regional Remote Sensing Centre, Kolkata an urban region, India located at the outflow of Indo-Gangetic Plain (IGP). Our ceilometer measurements of ABL height closely matched those obtained from radiosondes. However, reanalysis data could not capture all the layers present in ABL. Over Kolkata, significant diurnal and seasonal variations of ABL height is observed. Across all the seasons except winter, we observed a notable difference in ABL height between clear and cloudy days. This finding highlights the importance of considering weather conditions when interpreting ABL characteristics. We delved deeper into the ABL’s behaviour by analysing various characteristics including morning transition (MT) evening transitions (ET), nocturnal decay duration, and rate. Interestingly, the pre-monsoon season saw the fastest morning growth rates, reaching 150 m/hr. This was followed by the post-monsoon season (128 m/hr), the monsoon season (98 m/hr), and winter (90 m/hr). Additionally, we explored the relation between surface temperature and ABL processes. These results are useful for boundary layer parameterization and improve our understanding of air pollution dispersion models in urban regions.