African summer monsoon active and break spells cloud properties: Insight from CloudSat-CALIPSO

Abstract

Abstract This paper investigates the variability of monsoon clouds properties over the South African summer monsoon core zone (SAM: 20°-5°S; 12°-40°E) during the active and break spells of the monsoon seasons and compare the results to those Efon et al. (2016) observed over the West African summer monsoon (WAM) using CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellites merged data products. We first computed rainfall anomalies from the Tropical Rainfall Measuring Mission (dataset: TRMM-3B42) rainfall estimates for 1998–2016 to identify the active and break spells of the summer monsoon seasons. More break than active spells, especially in June occur over WAM, and over SAM, active spells are more common, especially in the month of January. Prolonged and successive rainfall can cause floods as observed in the 2010/2011 monsoon season over SAM. A comprehensive assessment is made of cloud properties during active and break spells. Both CBH and CTH exhibit trimodal distribution over SAM. Thicker clouds (with ΔH ≥ 3 km) occur more during the active than break spells. More cirrus cloud cells occur during the active spells (53%) than break spells (43%) over SAM and lesser deep convective clouds occur over SAM compared to WAM during the active spells. Mid-level clouds over SAM have more LWC and Rliq compare to those occurring over WAM. High-level clouds over SAM are richer in IWC, INC and Rice in both monsoons spells than those over WAM. Deep clouds over SAM have larger Rliq and Rice than those occurring over WAM. More atmospheric heating due to clouds in the active spells occur over WAM than SAM in the lower troposphere, and in the upper atmosphere, more heating of the atmosphere takes place SAM compare to WAM. This study has application in representing clouds better in regional weather and or climate models.