Mechanisms of Decadal Variability in the North Atlantic: The Thermohaline Circulation, Great Salinity Anomalies, and Gulf Stream Path

摘要/ abstract摘要：本研究旨在探讨北大西洋年代际变化的物理机制。重点探讨了大盐度异常（GSAs）对温盐环流、深西部边界流（DWBC）、北部再环流环流（NRG）和墨西哥湾流路径南北向转移的影响，认为GSAs是造成这种变化的重要因素。初步数值试验表明，GSA事件对年代际海洋变率的影响与风强迫变化（例如北大西洋涛动的变率）的影响一样大，如果不是更大的话，并且在年代际时间尺度上，其影响远远大于温室气体增加导致的辐射和地表热通量变化的影响。此外，GSA事件与温盐环流的相互作用可能导致气旋性NRG的年代际变化和墨西哥湾流路径的南北转移，从而影响美国东海岸的气候。方法是结合数值实验和理论来研究这些问题，使用简化的和综合的数值海洋模式，结合平板海冰模式和一个简单的大气模式。这些数值计算将通过对gsa性质的理论研究以及它们与温盐环流的相互作用如何导致NGR的变化和墨西哥湾流路径的南北移动，从而导致中纬度海洋环流的年代际变化来补充。除了气候变率之外，本研究还提出了一些长期关注的物理海洋学问题，即控制墨西哥湾流分离的机制，气旋NRG的下游路径和产生，以及GSA事件及其对热盐环流的重要性（或其他）。除了加深对海洋和气候变率的基本性质和原因的了解外，这项研究还将使人们更好地认识到高纬度海洋监测是否以及如何在预测和探测年代际气候变率方面是必要的

ABSTRACTOCE-0351383The proposed research is to investigate the physical mechanisms of decadal variability in the North Atlantic ocean. Particularly, it focuses on exploring the hypothesis that Great Salinity Anomalies (GSAs) are a significant contributing factor to such variability, through their effect on the thermohaline circulation, deep western boundary current (DWBC), northern recirculation gyre (NRG) and the north-south shifts of the Gulf Stream path. Preliminary numerical experiments indicate that GSA events have as much if not more effect on decadal ocean variability than do changes in the wind forcing (e.g., variability in the North Atlantic Oscillation) and, on decadal timescales, have a much larger effect than do changes in radiative and surface heat flux changes due to increased greenhouse gases. Furthermore, the interaction between GSA events and the thermohaline circulation may lead to decadal variations of the cyclonic NRG, north-south shifts of the Gulf Stream path and thereby affect the climate of the east coast of the USA. The approach is to investigate these issues with a combination of numerical experimentation and theory, using both simplified and comprehensive numerical ocean models, coupled to slab sea-ice models and a simple model of the atmosphere. These numerical calculations will be supplemented by theoretical investigations of the nature of GSAs and how their interaction with the thermohaline circulation may lead to variations of NGR and north-south shifts of the Gulf Stream path, and hence decadal changes in the mid-latitude ocean circulation. In addition to climate variability, the proposed research addresses some physical-oceanographic problems of long-standing interest, namely the mechanism governing the Gulf Stream separation, the downstream path and the production of cyclonic NRG, and the importance (or otherwise) of the GSA events and their effect on the thermohaline circulation. In addition to an increased understanding of the fundamental nature and causes of ocean and climate variability, the research will lead to a better sense of whether and how high-latitude ocean monitoring is necessary in predicting and detecting decadal climate variability