Cloud Phase Characteristics Over Southeast Asia from A-Train Satellite Observations

Abstract

Abstract. This study examines the climatological characteristics of cloud phase over Southeast Asia (SEA) based on A-Train satellite observations. Using the combined CloudSat-CALIPSO (CC) data, five main cloud groups are investigated: ice-only, ice-above-liquid, liquid-only, ice-above-mixed and mixed-only clouds that have annual mean frequencies of 27.8 %, 21.9 %, 16.9 %, 7.4 % and 6.2 %, respectively. Liquid-only clouds tend to occur in relatively cold, dry and stable environments. The other four cloud groups appear more frequently in relatively warm, humid and unstable conditions and their seasonal distributions move with large-scale climate systems: Asian monsoon and ITCZ. Liquid clouds are found to be highly inhomogeneous based on the heterogeneity index (Hσ) from Aqua MODIS, while ice-only and mixed-only clouds are often very smooth. Ice-above-liquid clouds are less inhomogeneous than liquid-only clouds due to the thin overlying ice clouds. Undetected subpixel liquid clouds enlarge clear sky Hσ, leading to some inhomogeneous clear sky pixels, which otherwise should be smooth. The reflectance at 0.645 (R0.645) and brightness temperature at 11 μm (BT11) of ice-only, liquid-only and ice-above-liquid clouds show peak frequencies near that of clear sky (R0.645 ~ 0.02, BT11 ~ 294 K), implying that a large population of thin or subpixel clouds over SEA are difficult to see by MODIS. The CC data also show abundant thin clouds over SEA, which indicates 78.3 % ice-only and 89.6 % ice-above-liquid clouds with ice τ