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

Abstract:

Satellite observations continue to play an important role in advancing our understanding of cloud phase and vertical structure and their roles in the Earth’s climate system. In this study, we use the combination of CloudSat-CALIPSO (CC) and MODIS observations to study the characteristics of cloud phase over Southeast Asia (SEA) – a region that hosts complicated cloud systems that are strongly influenced by the Asian monsoon, ITCZ, MJO and ENSO. We focus on the 3-D spatial patterns of cloud phase, including cloud overlap, the spatial heterogeneity signatures of cloud phase and how they vary over intraseasonal and interannual scales.

Using the combined CloudSat-CALIPSO data, five main cloud groups are investigated over SEA: ice-only, ice-above-liquid, liquid-only, ice-above-mixed and mixed-only clouds having annual mean frequencies of 28.6%, 20.1%, 16.0%, 9.3% and 6.7%, respectively. Liquid-only clouds tend to occur in relatively cold, dry and stable lower troposphere. The other four cloud groups appear more frequently in relatively warm, humid and unstable conditions and their seasonal distributions move with the Asian monsoon and the 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 more heterogeneous than ice-only clouds but more homogeneous than liquid clouds owing to ice clouds being optically thin and radiation emerging from low-level liquid cloud dominating. We demonstrate that the distribution of clear-sky Hσ has a long tail towards heterogeneous values that are caused by undetected sub-pixel cloud within both CC and MODIS datasets. The intraseasonal and interannual behaviors of all-sky Hσ signatures follow that of cloud phase and vary with the MJO and the ENSO phases