Long-term variability of the low-level clouds across Indo-Gangetic Plain

This study examines the long-term variability (1980–2022) of low-level clouds and their base heights using cloud observations from India Meteorological Department (IMD) over the Indo-Gangetic Plain (IGP) crucial for aviation. For this purpose, synoptic cloud observation data, coded as per World Meteorological Organisation (WMO) standards, were collected every three hours from four weather stations of IMD namely Amritsar, Delhi, Lucknow, and Patna. Highest prevalence of cloud types namely Stratus (St), Stratocumulus (Sc), Cumulus (Cu), and Cumulonimbus (Cb) was observed during monsoon than pre-monsoon. We have reported the occurrence of Cb clouds during monsoon in the range of 20–50 %. Sc clouds show diurnal variation, peaking at 00, 03 UTC, and 15, 18, and 21 UTC. Cu and Cb clouds exhibit maxima in the afternoon during pre-monsoon and monsoon seasons, possibly due to the diurnal cycle of the atmospheric boundary layer height variations. Monsoon cases surpass pre-monsoon at all IGP sites. Notably, Cb with CBH 600–1000 m causes maximum rainfall during monsoon, and predominant Cb base heights are 600–1000 m, 1000–1500 m, and 1500–2000m across decades. •The monthly climatological mean occurrence (1980–2022) reveal that different cloud types over all IGP sites exhibit peak during monsoon months compared to other months.•Among various cloud types, Cumulonimbus (Cb) clouds generally exhibit higher occurrence than St, Sc, and Cu clouds.•Notably, Cumulus (Cu) clouds over Amritsar display a higher occurrence compared to other sites.