Pathways of precipitation formation in different thermodynamic and aerosol environments over the Indian Peninsula

Abstract

This study examines precipitation pathways in different thermodynamic and aerosol environments over the Indian peninsula. A three-dimensional idealized Large-Eddy Simulation (LES) model with spectral bin microphysics is used to simulate convective clouds growing under different monsoon environments. Numerical simulations were evaluated using in-situ measurements from the Cloud-Aerosol Interactions and Precipitation Enhancement Experiment (CAIPEEX). Sensitivity studies were carried out using varied combinations of water vapor mixing ratio (by ±10 and ± 20%) and cloud condensation nuclei number concentrations (100 and 3000 cm−3). The response of various microphysical process rates to the changes in moisture and aerosol is analyzed. The clouds developed in a moist environment have a greater cloud depth, more supercooled liquid, broader cloud drop spectra, earlier onset of mixed-phase regimes, and enhanced precipitation. The amount of moisture is an important factor in determining the aerosol effects on cloud phase and precipitation, with a more significant aerosol impact in the moist environment (+ 20%). An increase in aerosol number concentration results in an enhanced mixed-phase fraction, updraft velocity, and precipitation, mainly through enhancing deposition and aggregation rates. The overall change in moisture by ±20% in cloud properties and precipitation is much more significant than the ten-times change in aerosol concentrations. The secondary ice formation via the Hallet-Mossop (H-M) process plays a significant role in determining the total ice crystal concentration, and its importance increases with the increases of both moisture and aerosol number concentration. The impact of this process on precipitation is minimal. These results provide an important understanding of how co-varied moisture and aerosols over the Indian region would affect the monsoon clouds and precipitation.