Tropical mesoscale convective system formation environments

Abstract

Mesoscale convective systems (MCSs) in the tropics play an integral role in the water cycle, are associated with local hazardous weather conditions, and have significant remote impacts on the midlatitude jet stream. Although it is known that MCSs occur in relatively moist environments, it is unclear how far in advance favorable ingredients (lift, instability, and moisture) in the mesoscale environment precede MCS formation. In this study, an automated MCS tracking algorithm and global reanalyses are used to examine the pre-MCS environment for 3295 MCSs that occurred in the tropics in a 3-month period. Results showed that increased water vapor and mesoscale ascent implied by low-level convergence and upper-level divergence preceded MCS formation by up to 24 h. Regional variations in pre-MCS environment conditions were apparent and are discussed. Future work will study to what extent these moisture and wind anomalies can be used to predict MCS formation.