Characterization of Convective Interactions with Easterly Waves, the Caribbean Low-Level Jet and Central American Topography During OTREC

点击翻译按钮获取中文摘要

This award supports work on the Organization of Tropical East Pacific Convection (OTREC) field campaign. The campaign seeks to understand 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 examines 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 full set of campaign awards is discoverable on the nsf.gov/awardsearch webpage by a keyword search on "OTREC".Tropical convection plays a critical role in earth's climate system and is also responsible for extreme precipitation and hurricane formation. Easterly waves are of particular interest for weather forecasting given their tendency to spawn hurricanes. More generally, tropical convection is an engine of weather and climate worldwide yet poorly understood and difficult to simulate. Work leading to better representation of tropical convection in weather and climate models can thus lead to better weather forecasts and impact assessments, both for the public and decision makers. Aside from the societal relevance of the science, the campaign includes several education and outreach activities including support for undergraduates to participate in fieldwork and production of short documentary videos for use in classroom teaching and informal science education. In addition, the project builds international scientific collaboration through partnerships with researchers in Costa Rica and Mexico. The project also supports fieldwork participation by three graduate students, and outreach to local students is conducted through short courses at the University of Costa Rica.The eight week OTREC deployment consists primarily of a set of 20 flights in the Gulfstream V (GV) research aircraft maintained by the National Center for Atmospheric Research (NCAR). The campaign uses an airport in Costa Rica for easy access to the equatorial Pacific and southwest Caribbean study regions, and conditions in these regions are sampled using dropsondes and a wing-mounted W-band radar. Dropsondes contain the same instrument package as standard weather balloons, only dropped from an aircraft (in this case from about 40,000 feet) with a small parachute. The radar determines cloud properties such as the relative abundance of ice particles versus liquid droplets, and uses Doppler shift to measure updraft and downdraft speeds in clouds. The aircraft sampling is augmented by observations collected at ground sites in Costa Rica and Colombia.The specific focus of this project is easterly waves, which play a dominant role in the variability of tropical convection and serve as precursors for hurricane formation. Easterly waves in the southwestern Caribbean are generally thought to propagate into the region from West Africa. But it is not clear whether easterly waves in the eastern Pacific originate locally or reintensify after crossing Central America from the Caribbean. Some studies suggest that formation or reintensification occurs through instabilities of strong low-level jets which occur where winds are funneled through gaps in the Central American mountains. Generation and intensification could also happen through interaction with convection, either over Central America or off the Pacific coast of Colombia, regions where a strong diurnal cycle produces episodes of intense convection and rainfall.The role of jet stream instabilities in generating or reinvigorating easterly waves is examined using data from meteorological analyses produced using observations from the OTREC campaign (provided by collaborators at ECMWF). The interaction of easterly waves with convection over Central America is examined using satellite data and surface meteorology stations in Costa Rica. These include GPS receivers already deployed as part of the COCONet network (see EAR-1042906), which record the total precipitable water vapor in the atmosphere. These assets are augmented with an additional 10 GPS ground stations and 10 surface weather stations, as well as two weather balloon launching stations. A key issue to be examined with the surface stations is the timing of the maxima in precipitable water vapor and precipitation, as the lag between the two (i.e. whether precipitation peaks first or precipitable water peaks first) provides valuable information regarding the organization and vertical structure of convection.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.