Collaborative Research: Examining the links between Atlantic Meridional Overturning Circulation and Atlantic Multidecadal Variability

点击翻译按钮获取中文摘要

It is well recognized that the meridional overturning circulation in the Atlantic Ocean (referred to as the AMOC) is an important factor controlling ocean heat transport in the North Atlantic, changes in this transport can affect ocean surface temperatures, atmospheric circulation and hence climate. Another notable feature of the North Atlantic seen in observations and models is the pronounced, spatially coherent, variability in the North Atlantic sea surface temperatures on decadal to multi-decadal timescales referred to as Atlantic Multidecadal Variability (AMV). With a typical periodicity of about 50 years, the AMV sea surface temperature (SST) variability impacts key climate characteristics, ranging from precipitation to tropical cyclone activity. The extent to which AMOC variability and the AMV are independent, and to which the latter reflects the former, remains hotly debated. One difficulty in resolving this debate is the short duration of available observations; another is that across the models, AMOC variability, including its periodicity, amplitude, and effect on SST, varies broadly. Accordingly, the main objective of this project is to establish the robust mechanisms of AMOC variability and its connection with the AMV, and at the same time to systematically explore the causes of these inter-model differences. This is of strong practical value as the AMOC is shown to be the most predictable component of the climate system on decadal timescales - progress in decadal prediction requires a better understanding of AMOC variability and its impacts. Funding from this grant will support the career growth of a female early career scientist, a graduate and undergraduate student and two postdoctoral associates. The project will enhance the climate modeling capacity by graduate and undergraduate students at both George Mason and Yale, and will facilitate the exchange of expertise between the two universities. This project will support several educational broader impacts including participation in GMU's Aspiring Scientists Summer Internship Program, benefiting high-school students and undergrads, public lectures and Teacher Development workshops at the Peabody Museum of Natural History.This is a modeling proposal to study decadal to multi-decadal variability of the Atlantic Meridional Overturning Circulation (AMOC) and its effect on climate in the North Atlantic, specifically on AMV, also referred to as the Atlantic Multidecadal Oscillation (AMO). The core approach lies in exciting or isolating AMOC internal modes and assessing their contribution to the AMV. The project will include several interrelated components: (i) Multi-decadal numerical experiments using several global climate models selected to represent inter-model differences in AMOC characteristics, in which we will excite AMOC variations by prescribing specifically chosen initial conditions - oceanic optimal initial perturbations in temperature or salinity. (ii) An analysis of the CMIP5 dataset focusing on AMOC internal modes and their effect on the AMV. (iii) A complementary analysis of an ocean eddy-resolving climate simulation. (iv) Observational analysis identifying periods of possible AMOC mode activity that we will then simulate with decadal reforecast experiments initialized by different ocean reanalysis products, thereby testing the impact of ocean state on the decadal evolution of the North Atlantic SST anomalies and the AMV. Throughout these analyses the properties of AMOC internal modes and the links between the AMOC and AMV will be assessed.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.