Organization of Tropical East Pacific Convection (OTREC) - Post-Campaign Analysis

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This award supports analysis of observations collected during the Organization of Tropical East Pacific Convection (OTREC) field campaign. The campaign was designed to study the formation and development of tropical convective clouds and associated heavy rainfall in the adjacent but distinct regions of the eastern equatorial Pacific and the southwest Caribbean, along with their evolution over the intervening portions of Central America and Colombia. The campaign also considered the genesis and evolution of easterly waves, large westward-moving atmospheric disturbances (wavelengths of about 2,000 km) which occur on a weekly basis in the Caribbean and eastern Pacific. The campaign deployment, based in western Costa Rica, took place from August to October 2019 and featured 22 flights of the Gulfstream V research aircraft maintained by the National Center for Atmospheric Research. The aircraft flew at about 40,000 feet using dropsondes and a W-band radar to make observations of clouds and atmospheric conditions. Dropsondes contain the same instrument package as standard weather balloons, only dropped from the aircraft with a small parachute. The radar determines cloud properties including the concentrations of ice particles and liquid droplets, and uses Doppler shift to measure cloud updraft and downdraft speeds. The aircraft sampling was augmented by observations collected at ground sites in Costa Rica and Colombia.This project continues the campaign's effort to identify the mechanisms that lead to the development of deep tropical convection. Much of the work is devoted to analysis of vertical mass flux profiles in convecting regions, in paticular whether rising motions in clouds occur in the lower to middle troposphere or the upper troposphere. The work is motivated by a theory of tropical convection developed by the Principle Investigators and others which emphasizes the association between bottom-heavy vertical mass flux profiles and heavy rainfall, as well as an inverse relationship between atmospheric stability and moisture content. Work here determines the extent to which the theory applies to all the OTREC study regions despite their differences in sea surface temperature and other conditions. The project also considers whether easterly waves found in the eastern Pacific form locally or if they are the same easterly waves seen propagating across the Atlantic after forming in West Africa. Additional work considers the impact of the Madden-Julian Oscillation (MJO), a large-scale topical weather pattern, on convection observed during the campaign. The MJO caused a shift in low-level wind direction during the campaign and the effects of the wind shift on convection are not yet clear. Finally, the research includes collaborations with the European Centre for Medium-range Weather Forecasts to evaluate weather forecasts in the OTREC study area, and with colleagues at the National University of Colombia who bring surface-based observations and regional expertise to the project.The work is of societal interest due to the importance of tropical convection for weather and climate across the globe. Easterly waves are of particular interest for weather forecasting given their tendency to spawn hurricanes. Better understanding of tropical convection and easterly waves is thus of interest for the improvement of weather and climate models and for helping decision makers anticipate the likely consequences of climate variability and change. The work also promotes international collaboration in atmospheric science through the collaborations mentioned above. The Principle Investigators pursue education and outreach through public lectures, a class on the "Science of Weather" for high school science teachers, and interactions with K-12 students. The project provides support and training to a graduate student and an undergraduate.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.