| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | March 29, 2018 |
| Latest Amendment Date: | March 29, 2018 |
| Award Number: | 1756658 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Baris Uz
bmuz@nsf.gov (703)292-4557 OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | May 1, 2018 |
| End Date: | April 30, 2023 (Estimated) |
| Total Intended Award Amount: | $339,589.00 |
| Total Awarded Amount to Date: | $339,589.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
4400 UNIVERSITY DR FAIRFAX VA US 22030-4422 (703)993-2295 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
4400 University Drive Fairfax VA US 22030-4422 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | PHYSICAL OCEANOGRAPHY |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
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.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The goal of this collaborative project between PIs at George Mason University (OCE-1756658) and Yale (OCE-1756682) is to study decadal, multi-decadal and longer variability of the Atlantic Meridional Overturning Circulation (AMOC) and its effects on climate in the North Atlantic, specifically on North Atlantic sea surface temperature (SST) and Atlantic Multidecadal Variability (AMV). Our core approach lies in isolating AMOC modes of variability and/or forcing AMOC variations externally in climate models and assessing the contribution of those variations to SST variability. In parallel, we investigate the fundamental physical mechanisms of AMOC stability, variability and change in a warming climate. Some of the key findings of this work are summarized below:
The predictability of North Atlantic SST and upper ocean heat content. We use a linear inverse model (LIM) to examine the predictability of North Atlantic SSTs and upper ocean heat content (UOHC) in observations spanning 1919 to 2018 and 1945 to 2012, respectively (Martin et al., In preparation). We find that basin-averaged SSTs are predictable at a time scale of 3-5 years. Regionally, SSTs in the Irminger Sea and Iceland Basin have the highest predictability within the North Atlantic. A similar spatial pattern is seen for UOHC predictability with the highest predictability of UOHC in the Irminger Sea and Iceland Basin, as well as parts of the Labrador Sea. The results suggest that thermal ocean memory storage in the subpolar gyre is a leading source of North Atlantic SST predictability.
Initialized versus uninitialized CESM2 Decadal Reforecasts. We have conducted anomaly initialized decadal reforecast experiments with the latest version of the Community Earth System Model (CESM2) to assess the skill of initialized versus uninitialized simulations. Preliminary results indicate that historical forcing plays a dominant role in driving North Atlantic SST variability in CESM2, but that initialization improves the reforecast, specifically in the subpolar gyre at 5-7 years lead (Erfani et al., In preparation).
AMOC multidecadal variability under different CO2 forcings. We studied AMOC multidecadal variation under different CO2 levels (Ma et al., 2021). Using CESM 1.0.4, we simulated AMOC variability under Last Glacial Maximum, preindustrial, and 4x preindustrial CO2. Rising CO2 led to shorter-period, weaker AMOC multidecadal variability due to increased North Atlantic stratification, altering westward propagating oceanic Rossby waves. We analyzed NAO linkages. Only preindustrial CO2 showed a significant negative correlation when the NAO leads the AMOC by 3-11 years
AMOC slowdown in a warming climate strengthens tropical cyclone activity. The AMOC is projected to weaken under greenhouse warming. We investigated the impacts of this weakening for 21st-century Tropical Cyclones (TCs) using the two global warming ensemble simulations (Liu et al. 2020, see OCE-1756682): one that exhibits AMOC weakening and the other in which we fix AMOC intensity. Using these experiments, we compute Genesis Potential Indices (GPI) and conduct downscaling TC simulations for the two scenarios. We find an enhancement of tropical cyclogenesis along the U.S. eastern seaboard in a warm climate with a weakened AMOC compared to that with a steady AMOC (Levin et al., In preparation).
Tropical Atlantic equatorial heat content and SST variability. Interannual tropical Atlantic Ocean SST variations impact atmospheric circulation, affecting precipitation over sub-Saharan Africa and northeast Brazil with important ecological and socioeconomic consequences. To gauge predictability, we explored equatorial warm water recharge and its link to eastern equatorial Atlantic SST anomalies (Turner et al., 2022). We found that while equatorial heat content changes do occasionally play a role in the development of boreal summer Atlantic zonal mode events, they contribute more consistently to Atlantic Nino II, boreal winter events. Event and composite analysis of ocean adjustment with a shallow water model suggest that the warm water volume anomalies originate mainly from the off-equatorial northwestern Atlantic.
See Yale's Project Outcomes Report (OCE-1756682) for a summary of key findings on:
- AMV-AMOC links
- The impacts of the AMOC slowdown in a warming climate
- The effect of enhanced Indian ocean warming on the AMOC
- AMOC stability and sensitivity to external perturbations
- AMOC slowdown and recovery under a steady external forcing
Funding from this grant supported collaboration between PI Fedorov at Yale and a female early career researcher, PI Burls, at George Mason University (GMU). This project supported two graduate students at GMU, one of whom graduate with their MS thesis in Climate Science. This grant also supported internship opportunities for 15 high school students and 2 undergraduate students through PI Burls' involvement in GMU's Aspiring Scientists Summer Internship Program. Burls co-authored 3 publications and there are three more manuscripts associated with this award in preparation. The results from this collaborative project have also been presented at invited and regular talks/posters by the PIs at the AGU, EGU, Ocean Sciences and other conferences and workshops. Lastly, this project enhanced the capacity for global climate modeling and analysis by graduate and undergraduate students at both George Mason and Yale.
Last Modified: 08/29/2023
Modified by: Natalie Burls
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