Precipitation Characteristics of Easterly Waves Across the Global Tropics

Tropical easterly waves (TEWs) are a recurrent mode of low-latitude weather that are often convectively coupled and impact precipitation extremes. Previous work has examined the development of TEWs and their associated precipitation for individual seasons or regional domains, but no studies exist that document the importance of TEW precipitation globally. This study quantifies the precipitation associated with TEWs across the entire tropics using satellite (Integrated Multi-satellitE Retrievals for the Global Precipitation Measurement [IMERG]) and reanalysis (Modern-Era Retrospective analysis for Research and Applications, Version 2 [MERRA-2]) data. Traditional space-time filtering of precipitation reveals a mostly similar climatological power distribution for westward traveling, synoptic period disturbances corresponding to TEWs within all data sets. Using objective tracking, we find that areas with maximum TEW frequency such as the North Atlantic, Equatorial Pacific, and Indian Ocean have the highest accumulation of TEW-associated precipitation. TEWs account for at most 30% of total annual precipitation in regions where they commonly occur and 1%-5% over much of the tropics. Vertically collocated storms, where the 850 and 700 hPa tracks correspond with each other, have higher conditional rain rates and indicate that waves with vertical development produce stronger and more organized convection. We find similar regional patterns using MERRA-2 precipitation and latent heating, although the importance and contribution of TEWs to the background are reduced compared to IMERG. While the broad pattern of TEW associated precipitation in MERRA-2 is like observations, the underestimation of rainfall contributions from TEWs, coupled with occasional false alarms in reanalysis data, suggests that MERRA-2 does not capture organized convection within TEWs correctly. Tropical easterly waves (TEWs) are a common weather feature in the tropical atmosphere. TEWs are linked to increased rainfall, especially over West Africa and the tropical North Atlantic, however no tropics-wide analysis of rainfall associated with TEWs has been performed. To address this gap, this study uses multiple methods and data sets to examine the contributions TEWs make to tropical rainfall. Using techniques designed to extract waves based on their size and frequency, we find that TEWs are important in all data sets and precipitation associated with TEWs maximizes where these waves most commonly occur. We find that TEWs contribute upwards of 20%-30% of the annual average rainfall across the tropical North Atlantic and Pacific with generally higher contributions over oceanic regions. Vertically developed waves that are present at multiple levels in the atmosphere, on average have higher rainfall rates despite being less common than non-vertically developed waves. Finally, we find that TEWs represent a higher percentage of the annual rainfall when using observational estimates from satellite data as simulated precipitation from numerical models underestimates TEW rainfall. An objective tracking method for easterly waves reveals more regional variability in associated precipitation than space-time filtering Easterly waves account for at most 30% of total annual precipitation in regions where they commonly occur and 1%-5% over much of the tropics Reanalysis data underestimates the importance and percent contribution of tropical easterly wave precipitation compared to observations