Distinct Diurnal Cycle of Supercooled Water Cloud Fraction Dominated by Dust Extinction Coefficient

Abstract

AbstractCloud phase (CP) partitioning (e.g., supercooled water cloud fraction, SCF) is often misrepresented in model simulations. One of the remarkable uncertainties involves the poor understanding of SCF diurnal cycle due to lack of observations. By using 33 months of lidar observations from Cloud‐Aerosol Transport System which provides cloud top phase at different local times for a given grid and isotherm, this study first characterizes the diurnal cycle of SCF between 51°S and 51°N. Distinct SCF diurnal variations have been found near‐global at different isotherms, especially for −22.5°C, where SCF diurnal ranges even reach 60%. Correlation analysis shows a robust dependence of SCF diurnal cycle on the variation of dust aerosol extinction coefficient instead of other dust load indicators and meteorological parameters. Given the important roles of SCF on the radiation budget, this study will help us better constrain aerosol‐cloud interaction and simulations of CP partitioning in models.