The Organization of Tropical East Pacific Convection (OTREC) Field Campaign:  Support for Field Activities and Post-Campaign Analysis

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项目编号	1758513
	The Organization of Tropical East Pacific Convection (OTREC) Field Campaign: Support for Field Activities and Post-Campaign Analysis
	David Raymond
主持机构	New Mexico Institute of Mining and Technology
项目开始年	2018
	2018-03-15
项目结束日期	2021-02-28
资助机构	US-NSF
项目类别	Continuing grant
项目经费	226087(USD)
国家	美国
语种	英语
英文摘要	This grant 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 Columbia. 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 grants 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 Principal Investigators (PIs) of this grant incorporate results from the campaign into their outreach to New Mexico high schools, in part through a class on weather and climate offered in the Masters of Science Teaching program at New Mexico Tech. They also develop materials for K-12 classroom teaching in their state. The project supports a graduate student and a postdoctoral research fellow, thereby providing for the future workforce in this research area. The eight-week OTREC deployment consists primarily of a set of 20 flights of 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. Despite intensive study we lack a satisfactory theory for how environmental conditions determine when and where tropical convection will form, how long it will last, how much it will expand and organize, and how much rain it will produce. The PIs have developed a theory in which deep convection over warm oceans is controlled by three thermodynamic factors: heat and moisture coming from the underlying ocean, the "saturation fraction" of the atmospheric column (a kind of bulk relative humidity), and moist convective instability (with a counterintuitive association between weaker instability and heavier rainfall). But the theory assumes uniform atmospheric and oceanic conditions, and this assumption may not hold in the eastern equatorial Pacific. Instead, the region features a large north-south contrast in sea surface temperature (SST) accompanied by a narrow east-west convection band called the intertropical convergence zone (ITCZ). The sharp SST contrast provides an alternative explanation for ITCZ convection, as near-surface winds generally blow across the temperature contrast and converge over the warmer SSTs. Rising motion where low-level winds converge can produce convection, but the observed convection does not clearly match expectations based on SST contrast arguments. A further issue involves the vertical structure of convective clouds, as convective clouds in the eastern Pacific ITCZ are relatively shallow yet they produce rain rates similar to their deeper counterparts over the western Pacific. The PIs have an explanation for the development of heavy rain from mid-depth convection which can be tested using campaign data. A further mystery is that satellite data from the NASA Tropical Rainfall Measurement Mission (TRMM) seem to show a large amount of stratiform rain in the eastern Pacific, even though high stratiform rain fraction is usually associated with the anvil cloud and decaying cloud plumes found in regions of deep convection. The PIs argue that cloud features identified as stratiform rain in TRMM data should instead be classified as weak cellular convection, thus removing the inconsistency between stratiform rain amounts and relatively shallow convection. The combination of dropsonde and airborne radar data should suffice to distinguish between stratiform rain clouds and weak cellular convection. In contrast, SSTs in the southwest Caribbean are quite uniform so convection does not develop from SST-induced wind convergence. Moreover, mid-tropospheric air over the area is relatively dry and thus not conducive to convection and heavy rainfall. Yet convection and heavy rainfall still occur, often associated with the passage of easterly waves. These waves appear on a weekly basis and sometimes cross Central America to reach the eastern Pacific. But it is not clear whether the majority of easterly waves in the eastern Pacific come from the Caribbean or if they form locally. These issues are also addressed in the campaign. 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.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/72415
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	David Raymond.The Organization of Tropical East Pacific Convection (OTREC) Field Campaign: Support for Field Activities and Post-Campaign Analysis.2018.