Why is there a meridional overturning circulation in the Atlantic Ocean but not in the Pacific?

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项目编号	1634128
	Why is there a meridional overturning circulation in the Atlantic Ocean but not in the Pacific?
	Paola Cessi
主持机构	University of California-San Diego Scripps Inst of Oceanography
项目开始年	2016
	2016-09-01
项目结束日期	2019-08-31
资助机构	US-NSF
项目类别	Standard Grant
项目经费	523574(USD)
国家	美国
语种	英语
英文摘要	In the current climate system, deep water is formed in the North Atlantic, but not in the North Pacific, resulting in a meridional overturning circulation (MOC) which transports heat everywhere northward in the Atlantic. Higher surface salinity in the North Atlantic relative to the North Pacific controls the position of the sinking branch of the MOC. Enhanced Atlantic salinity is partially due to the northward advection of salt by the Atlantic MOC (AMOC). In principle, this oceanic salt-advection feedback should allow a Pacific MOC (PMOC), but this is not observed in the present geometrical configuration of the global ocean. Moreover, the current generation of climate models do not accurately reproduce the MOC and the causes are unclear. Thus, many key questions remain to be answered regarding the dynamics of the MOC and consequently "Why is there an AMOC and not PMOC?". This project hypothesizes that the greater width of the Indo-Pacific compared to the Atlantic disfavors oceanic transport of salinity to the north. Specifically, the northward velocity in the upper branch of the MOC is larger for a narrow basin, favoring the salt-advection feedback in the Atlantic over the Indo-Pacific. This study will help to identify the factors controlling the strength of the MOC, which in turn has a large impact on the heat- and ice-content in high latitudes. A graduate student will enrich his/her knowledge in physical oceanography, climate dynamics and the scientific method, and be trained in mathematics, numerical modeling and modern scientific computations. A public, televised presentation will inform citizens on the achievements, limitations and future prospects of climate science. The hypothesis of 'the larger MOC northward velocity in the narrower basin occurs' is based on the argument that 1) the total MOC transport is independent of the sinking location; 2) the upper branch of the MOC is steered by the wind-driven gyres over a narrower region. The approach to test this hypothesis and quantify the processes penalizing the PMOC is to use ocean models in idealized geometries spanning a range of complexities: (i) 0-dimensional models of the budget of volume and salt transport ("box-models"); (ii) 2-dimensional advection diffusion equation of salt as a passive tracer; (iii) 3- dimensional ocean-only primitive equation models, both forward and adjoint. This suite will determine the sensitivity of high-latitude salinity and cross-equatorial volume transport on the external forcing. In addition to identify the fundamental oceanic processes favoring the AMOC over the PMOC in an idealized setting, this work will also complement the numerous studies in realistic geometries and with coupled air-sea exchanges. The use of the adjoint method in an idealized setting will efficiently explore the sensitivity of high latitude salinity on the forcing (wind-stress, surface temperature, freshwater flux) on time-scales up to 300 years, which is an order of magnitude larger than previously used.
来源学科分类	Geosciences - Ocean Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/70310
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Paola Cessi.Why is there a meridional overturning circulation in the Atlantic Ocean but not in the Pacific?.2016.