Clouds Over Delhi‐NCR: Three‐Year Analysis of Cloud Base Height, Types, and Seasonal Variability From Ceilometer Depolarization Measurements

Abstract This study presents a 3‐year, high‐resolution analysis of cloud vertical structure over Delhi–National Capital Region (NCR) using ceilometer observations from January 2022 to December 2024 at the CAS‐AO site in Sonipat, India. With over 95% data availability, we document cloud frequency, base height, layering, and phase in a region marked by strong seasonal variability, persistent aerosol loading, and complex boundary‐layer dynamics. Average cloud occurrence was 28.35%, dominated by single‐layer clouds (71.35%), with the highest frequency during the monsoon (46%) and lowest during the post‐monsoon (10%). The vertical distribution of cloud base height (CBH) was skewed toward low altitudes, with over half of the lowest cloud bases (CBH1) detected below 1 km and the highest CBHs reaching up to 15 km. Seasonal CBH variability reflected dominant thermodynamic controls: winter clouds were shallow and capped by surface inversions, while pre‐monsoon CBH1s peaked at ∼4 km due to elevated lifting condensation levels from intense surface heating. Monsoon clouds exhibited a bimodal CBH distribution associated with shallow cumulus and deep convection. Depolarization retrievals showed strong vertical stratification in the cloud phase, with liquid‐phase clouds at low levels, mixed‐phase in mid‐levels, and ice‐phase at higher altitudes. Multi‐layer clouds though less frequent (8.1%), were favored during convectively active and humid periods. Cloud occurrence strongly correlated with relative humidity and anticorrelated with temperature and solar radiation. ERA5 reanalysis underestimates mean CBH by ∼1.5 km and overestimates cloud occurrence across seasons despite excluding fog from its CBH diagnostic and underrepresenting high clouds, underscoring the need for ground‐based observations to improve cloud representation.