Tracking mesoscale convective systems in IMERG and regional variability of their properties in the tropics

Mesoscale convective systems (MCSs) constitute only a fraction of convective systems in the tropics but significantly impact tropical weather and global climate. Early studies used satellite infrared (IR) data to track MCSs and study their properties but only for a short period due to computing limitations. Though valuable, the IR brightness temperature (Tb)-derived precipitation properties have biases. The recent availability of Integrated Multi-satEllite Retrieval for Global (IMERG) precipitation mission rainfall data of lesser bias than IR Tb-based rainfall and access to high-performance computers motivated us to track MCSs over global tropics for 10 years, using the Forward in Time (FiT) algorithm. Though IMERG is advantageous, it poses challenges to tracking MCSs due to convective systems connected by light rain areas and resolution differences between contributing passive microwave sensors. The precipitation field is smoothed and normalized to overcome these problems; then, the FiT algorithm identifies MCSs and tracks them. Our results show that MCSs contribute similar to 70% of annual precipitation, though they are only similar to 7% of all tracked systems. MCSs occur more often over the Amazon basin and Maritime Continent than in central Africa, known for high thunderstorm frequency, highlighting the contrasting convective regimes. The large, long-lived, and intensely precipitating MCSs occur more often over the ocean than land, except for the Amazon basin. Fast-moving MCSs often occur over West Africa, the Amazon basin, and the western Pacific, whereas slow-moving MCSs are common over Colombia and the Maritime Continent.