Tracking Subtropical Water Mass Anomalies to the Tropics and Their Potential for Re-emergence

GSTDTAP

项目编号	1830007
	Tracking Subtropical Water Mass Anomalies to the Tropics and Their Potential for Re-emergence
	Susan Wijffels
主持机构	Woods Hole Oceanographic Institution
项目开始年	2018
	2018-09-01
项目结束日期	2021-08-31
资助机构	US-NSF
项目类别	Standard Grant
项目经费	760573(USD)
国家	美国
语种	英语
英文摘要	How tropical oceans, which are strong drivers of global climate variability, are influenced by subtropical processes remains unresolved. Tropical-subtropical teleconnections occur either via the atmosphere, which can set up within a season, or through subsurface ocean pathways operating over years to decades. The formation in the subtropics and subsequent advection of anomalous heat due to water mass anomalies is a potentially important ocean pathway. Some theoretical studies suggest this process controls multiyear to decadal climate variability. Anomalies are created in two ways: at the surface by wind, heat and freshwater flux changes or in the subsurface by anomalous advection. Using the recent record from the Argo array of profiling floats, many regional studies have identified the formation and propagation of water mass anomalies in most ocean basins. Modern ocean general circulation model studies with realistic surface forcing can form and advect anomalies similar to the observed ones. However, the two descriptions do not agree on whether these anomalies can survive to reach the equator, and then re-emerge to the surface. This project will take a globally consistent observational and modelling approach to quantitatively understand the source, fate and potential re-emergence of subtropical water mass anomalies, and thus their potential to influence the climate. As part of this project, an improved gridded global Argo analysis will be made freely available with particular focus on water mass variability and realistic estimates of resolved scales and errors. A production system will be put in place to ensure ongoing updates and distribution of the analysis. A graduate student in the MIT-WHOI Joint Program will learn both numerical modelling (including the analysis of ensembles) and observational analysis techniques. Since the targeted processes are a prime candidate for enabling longer term climate forecasting, results will discussed directly with climate forecasting teams in the US and Australia via collaborator Peter Oke. This project will combine a novel analysis of Argo data with a set of tailored ensembles of OGCM runs to identify source regions of observed water mass variability. A model-based ensemble optimal interpolation (OI) will be used for the first time to map Argo data, both on depth and density surfaces. Global observed surface conditions will be used to force a numerical model specifically configured and tuned to simulate the water mass variability in the Argo period. This all-forcing ensemble will then be compared to parallel ensembles with restricted tropical and subtropical/hemispheric forcing where the temperature, salinity and wind components will be varied to examine the generation and fate of anomalies generated in different regions. The goal is to attribute observed equatorial variability in each ocean basin to local and/or remote drivers and assess if there is any evidence for re-emergence. Examining all basins, which vary in source strength, advective pathways, mixing rates and throughflows, will result in a more unified view of where and when subtropical variability impacts the far field. The observational approach will involve carefully checking and removing sensor errors and using a dynamically-intelligent model-based ensemble OI framework. Rather than diagnosing formation mechanisms through incomplete observations or from a single all-forcing model run, the study will use dedicated ensembles of simulations with controlled regional surface forcing. An ensemble approach will clearly quantify the role that intrinsic variability (due to instabilities) plays in the model system and in turn, will help better understand the observed record. By focusing on the feeder flows to the equatorial upwelling systems, the team will then assess the importance of the proposed ocean tunnel to climate. 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/73391
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Susan Wijffels.Tracking Subtropical Water Mass Anomalies to the Tropics and Their Potential for Re-emergence.2018.