| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | April 5, 2017 |
| Latest Amendment Date: | April 5, 2017 |
| Award Number: | 1657209 |
| 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: | April 1, 2017 |
| End Date: | March 31, 2021 (Estimated) |
| Total Intended Award Amount: | $797,848.00 |
| Total Awarded Amount to Date: | $797,848.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
615 W 131ST ST NEW YORK NY US 10027-7922 (212)854-6851 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
61 Route 9W Palisades NY US 10964-8000 |
| 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): |
PREEVENTS - Prediction of and, 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
The winters of 2013/14 and early 2015 across the Northern hemisphere included chronic drought in California, extreme cold and snowy winters in northeast North America and severe floods in the U.K. Observational analyses and modeling have linked these disparate climate extremes to sea surface temperature (SST) anomalies. The SST anomalies in the tropical Indian and Pacific Oceans that have been invoked are distinct from those associated with El Nino or La Nina. The SST anomalies were warm in the Southern Indian Ocean and Western Tropical Pacific and neutral to cool around the maritime continent and central Equatorial Pacific Ocean. A recent analog to that state was the winter of 1990/91. A second example of an extremes-generating ocean state is that of persistent, multiyear cold conditions in the Central Equatorial Pacific Ocean. For the last century and a half for which SST records exists, extreme drought in western North America has been associated with such Tropical Pacific Ocean conditions. 1999 to 2002 was one such recent state. In contrast to El Nino and La Nina events, the ocean dynamics and thermodynamics of these two extremes-generating states have not been extensively studied. This project will conduct a detailed analysis of the ocean dynamic and thermodynamic processes that cause the oceans to adopt these SST patterns. The ocean states to be studied generate droughts, floods, extreme cold and snow across the globe, particularly in North America and Europe. The societal impacts of these events have been large. Improving their prediction and the understanding of their frequency of occurrence and intensity are key to enabling adaptation and disaster preparedness. Prediction requires understanding and the proposed work will advance understanding of the oceanic causes of the SST anomalies responsible for them, thus enabling advances in prediction and characterization of ocean-forced weather and climate extremes. The results of the study will improve our capability to model and forecast such hazards and events. Further, results generated in this work will readily be communicated to the communities that can advance efforts for prediction, societal planning and adaptation via lead investigator's close involvement in NOAA's Drought task force and the National Integrated Drought Information System's Task Force. The data created will be served via the International Research Institute of Columbia University's Data Library and be available as a research resource to the entire community.
The project is centered on the analysis of the momentum and heat budgets of the upper oceans contained within three ocean reanalyses: the European Center for Medium Range Weather Forecasts' Ocean Reanalysis (1958 to present), the consortium for Estimating the Circulation and Climate of the Ocean (Version 4, 1993 to present) and the Geophysical Fluid Dynamics Laboratory's Ensemble Climate Data Assimilation system (1960 to present). The contributions of surface fluxes, vertical mixing and dynamical ocean heat convergence by the mean flow and transient eddies will be evaluated for the extremes generating states using standard numerical procedures. Dynamical and mixing contributions will be related to changes in upper ocean heat content and to changes in currents and vertical motion which in turn will be related to wind stress forcing. Guided by a series of hypotheses, the causes of the extremes-generating ocean states will be determined to the extent allowed by data accuracy and sample size limitation. Long term trends in the ocean reanalyses and surface fluxes, as well as ensembles of climate model simulations, will be examined for any evidence that human-driven climate change is altering the probability of extremes-generating ocean states and the physical reasons why. The project will provide a comprehensive assessment of the oceanographic and ocean-atmosphere causes of the ocean states associated with two important extremes-generating SST anomalies. This work, largely observationally-based, will determine the physics underlying oceanic causes of recent climate and weather extremes.
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 tropical oceans play an outsize role in global climate. Heat released from the tropical oceans helps drive the global atmospheric circulation influencing climate worldwide. The sea surface temperatures (SSTs) of the tropical oceans continually change as a component of natural atmosphere-ocean variability. When they do so they also drive changes in atmospheric circulation that generate climate and weather anomalies worldwide. For example, cold states of the tropical Pacific Ocean drive droughts in North America, some of which can last for years or even decades. Changes in tropical Pacific SSTs in response to rising greenhouse gases (GHGs) also will lead to changes in regional climates worldwide.
Our project aimed to understand the physical mechanisms that cause changes in tropical SSTs, arising as part of natural variability, or in response to rising GHGs, and how these could cause climate and weather extremes worldwide. A major finding of our project is that state-of-the-art climate models likely misrepresent the response of the tropical Pacific ocean-atmosphere system to rising GHGs. For decades now it has been noticed that while the tropical Pacific has generally warmed the equatorial central to eastern Pacific has not warmed. This is a region of intense upwelling of cold waters from below and we hypothesize that this cooling effect has successfully offset the warming due to rising GHGs. In contrast, climate models tend to warm this region. Figure 1 shows the observed SST trends since 1958 and the response to rising GHGs in state-of-the art climate models. We have shown that this model bias could be a result of the poor representation in these models of the climatological state of the tropical Pacific. This model bias will have impacts on how these models project regional climate change and so is a matter of great importance.
In our project we have also examined how SST variations arising from internal climate variability can influence climate worldwide. We have conducted studies of how SST anomalies in the tropical Indo-Pacific Ocean in summers can drive changes in atmospheric circulation that lead to dry, hot conditions in the US Midwest and suppress corn yields. We have also shown how a proper representation in forecast models of the exchange of heat at the atmosphere-ocean interface is required if these events are to be predicted. We have also studied the relation between California winter precipitation and Indo-Pacific SSTs. We have hypothesized that the observed tropical Pacific warming, but lack of warming in the cold upwelling region, might be tipping the atmospheric circulation towards favoring a high-pressure ridge and dry winters at the North American West Coast. We have also shown that while tropical Pacific SSTs exert limited influence on California precipitation, when the SST anomalies are strong in the eastern equatorial Pacific and in the spring season there is a much higher likelihood that they will influence California precipitation. This result was applied to helping understand recent winter precipitation anomalies over California.
We have also uncovered the mechanisms that cause persistent cold states of the tropical Pacific Ocean. These cold states tend to drive persistent, multiyear, droughts over North America as well as droughts and wet periods elsewhere around the world. We used observations and models to show that these cold states likely arise from processes internal to the tropical Pacific Ocean and need not require forcing of the tropical Pacific from other ocean basins. We have also conducted studies of how the trend towards a strengthened east west and vertical temperature gradient in the tropical Pacific Ocean might be leading to stronger El Nino events which would likely strengthen climate and weather extremes worldwide.
We also conducted a study of the Great Global Famine of 1876-78. This famine led to the deaths of tens of millions of people, mostly in Asia, but also in Africa and Brazil. We showed how the droughts that initiated the famines and disease were related to the coincidence of several extreme climate states, including one of the largest El Nino events in the last two centuries. This was the first detailed study of the climate anomalies that led to one of the worst disasters that humanity has ever faced. Relatedly, we have shown how in the modern period SST anomalies globally can lead to synchronous crop production failures that disrupt the global food trade and food security. The tropical Pacific again plays a key role in these but the Indian and Atlantic Oceans are also important.
In summary, our project had led to improved understanding of the role of the oceans in driving extreme climate anomalies worldwide and how the SST anomalies responsible are generated. This work will lead to advances in modeling and predicting these SST changes both as natural events and as responses to rising GHGs.
Last Modified: 07/30/2021
Modified by: Richard Seager
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