The behavior of cloud base height over a hilly remote station of North-East India using ground-based remote sensing technique

Abstract

Impact of clouds and their vertical structures on the radiative budget, hydrological cycle, and climate is strong but still uncertain. There is a need to monitor and investigate cloud characteristics continuously to improve our knowledge and understanding. The behavior of the Cloud Base Height (CBH) is studied over Umiam, situated in a complex terrain of the Shillong Plateau. CBH measurements are obtained from a LIDAR Ceilometer and a comprehensive analysis of its characteristics covering from February 2019 to January 2022 has been presented here. Cloud occurrences showed distinct seasonality with maxima in wet months and minima in dry months. Multilayer cloud structures are found mostly in the monsoon season, although single-layer clouds dominated throughout the year. During the whole study period, the average frequency of occurrences of single, double, and triple layers of clouds are found at 38.5%, 11%, and 0.01% respectively against a total observation point of 78%. Near-ground cloud occurrences are ubiquitous with a maximum in July 2020 (18.08%) and a minimum in April 2021 (0.03%). CBH is found to vary with seasons too with higher bases during pre-monsoon months and lower during monsoon and post-monsoon months. Nighttime and early morning maxima in cloud occurrences are noted in some seasons. Cloud formation and occurrences are found to follow a pattern of existing circulation, dominated by local circulation during post-monsoon and winter and synoptic circulation during pre-monsoon and monsoon seasons. A comparison study of CBH with corresponding reanalysis datasets showed their inability to capture cloud representation over sloped terrain.