Influence of covariance of aerosol and meteorology on co-located precipitating and non-precipitating clouds over Indo-Gangetic Plains

Abstract. Aerosol-cloud-precipitation-interaction (ACPI) plays a pivotal role in the global and regional water cycle and the earth’s energy budget; however, it remains highly uncertain due to the underlying different physical mechanisms. Therefore, this study aims to systematically analyze the effects of aerosols and meteorological factors on ACPI in the co-located precipitating (PCs) and non-precipitating clouds (NPCs) clouds in winter and summer seasons by employing the long-term (2001–2021) retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS), Tropical Rainfall Measuring Mission (TRMM), and National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-II datasets over the Indo-Gangetic Plains (IGP). The results exhibit a decadal increase in aerosol optical depth (AOD) over Lahore (5.2 %), Delhi (9 %), Kanpur (10.7 %) and Gandhi College (22.7 %) and decrease over Karachi (-1.9 %) and Jaipur (-0.5 %). The most stable meteorology with high values of lower tropospheric stability (LTS) is found in both seasons over Karachi. In summer season the occurrence frequency of clouds is high (74 %) over Gandhi College, 60 % of which are PCs. Conversely, the least number of PCs are found over Karachi. Similarly, in winter season, the frequency of cloud occurrence is low over Karachi and high over Lahore and Gandhi College. The analysis of cloud top pressure (CTP) and cloud optical thickness (COT) indicate high values of cloud fraction (CF) for thick and high-level clouds over all study areas except Karachi. The micro-physical properties such as cloud effective radius (CER) and cloud droplet number concentration (CDNC) bears high values (CER > ~ 15 µm and CDNC > ~ 50 cm-3) for both NPCs and PCs in summer. The AOD-CER correlation is good (weak) for PCs (NPCs) in winter. Similarly, the sensitivity value of the first indirect effect ( FIE ) is high (ranged from 0.2 ± 0.13 to 0.3 ± 0.01 in winter, and from 0.19 ± 0.03 to 0.32 ± 0.05 in summer) for PCs and low for NPCs. Sensitivity value for second indirect effect (SIE) is relatively high (such as 0.6 ± 0.14 in winters and 0.4 ± 0.04 in summer) than FIE. Sensitivity values of the aerosol-cloud interaction (ACI) are low (i.e., -0.06 ± 0.09) for PCs in summers. Furthermore, the precipitation rate (PR) exhibits high values in summer season, and PR values are found high in comparatively thin clouds with fewer CDNC (< ~ 50 cm-3) and intermediate for optically thick clouds with higher CDNC (> ~ 50 cm-3 ).