Annual Cycle of Tropical Convective Clouds from 20-Year MODIS Observations with an Improved Convective Cloud Detection
Journal Article
Overview
abstract
Abstract; This study utilizes a 20-yr (2003–22) dataset of tropical deep convective clouds (DCCs) from MODIS wide-swath observations with a new detection method to characterize the annual cycle of tropical DCCs, focusing on global patterns, regional variations, and day/night differences. Tropical mean daytime DCC occurrence peaks in December (1.90%) and reaches a minimum in May (1.55%). Notable features include the double ITCZ over the eastern Pacific in March–April and alternating northwest–southeast bands of day/night differences over the Amazon. Regional analyses across six tropical regions, using four DCC size classes (class 1 “small” to class 4 “giant”), reveal distinct behaviors: The western Pacific has the highest DCC occurrences, driven primarily by giant clusters; the eastern Pacific shows similar seasonal trends across all classes; the equatorial Atlantic lacks growth of class 4 clusters; Africa consistently shows larger nighttime cluster sizes; and the Amazon features an alternating day/night dominance in DCC occurrences, with larger nighttime occurrences from May to August but smaller values from October to December. Distributions of normalized DCC cluster number density and occurrence as a function of cluster size show that larger clusters (>104 km2) dominate total convective area, despite the numerical dominance of smaller clusters (<103 km2). Oceanic regions exhibit unique patterns of day/night differences, characterized by fewer clusters smaller than 102.5 km2 and larger than 105 km2, but more clusters in the intermediate range during nighttime. These findings provide valuable information for model evaluations, highlighting the importance of resolving DCC cluster size variability in climate models.
