On the cloud radiative effect for tropical high clouds overlying low clouds

Abstract

Since high and low clouds ubiquitously overlie the Tropical Western Pacific (TWP) region, the cloud radiative effect (CRE) cannot be influenced by either high or low clouds, but by combinations of the clouds. This study investigates the CRE of multi-layered clouds in TWP via a radiative transfer model, Streamer. We assumed that multi-layered clouds are composed of full coverage of high clouds overlying low clouds with fractional coverage. The simulation results show that low clouds readily change CREs from positive to negative in the case of optically thin high clouds, even if the fraction of low clouds takes 10% of that of high clouds. Also, various combinations of physical properties of multi-layered high and low clouds allow more CRE variability (− 253.76 to 93.10 W m−2) than single-layered clouds do (− 101.62 to 96.95 W m−2). Even in the same conditions (total column cloud optical thickness = 15 and high cloud top pressure = 200 hPa), the multi-layer clouds have various CREs from − 180.55 to 45.64 W m−2, while the single-layer high clouds − 2.00 W m−2. These findings are also comparable with satellite observations from CERES and CALIPSO. The present study suggests that considerable uncertainty of radiative effects of high clouds over TWP can attribute to low clouds below high clouds.