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Modeling Effects of Greenland Ice Sheet Melting on AMOC Variability and Predictability.

Principal Investigator(s): Andreas Schmittner, Oregon State University

Year Initially Funded: 2013

Program (s): Climate Variability and Predictability


Award Number: | View Publications on Google Scholar

Recent observations reveal accelerated melting of the Greenland Ice Sheet (GrIS). Projections of future effects suggest continuing ice loss at increasing rates for business-as-usual anthropogenic greenhouse gas emissions scenarios. Additional meltwater fluxes into the surrounding North Atlantic ocean will increase the buoyancy of surface waters, which may reduce their rates of convection, subduction and sinking to the deep ocean and hence slow down the AMOC. Detailed estimates of the GrIS mass balance show that it is influenced by North Atlantic climate variability, suggesting a possible feedback between the GrIS and the AMOC. However, most comprehensive climate models currently do not include interactive ice sheets. Thus projections of future climate change performed with these models (including CMIP5) do not consider impacts of GrIS melting on AMOC variability although it is well known that the AMOC is sensitive to freshwater fluxes to the North Atlantic. The probabilities of AMOC reduction and shutdown for a given greenhouse gas emission scenario are therefore poorly known. Moreover, previous studies of AMOC internal variability and predictability did not consider feedbacks between the GrIS and the AMOC. Here we propose to organize a model intercomparison project, involving the major climate modeling centers around the world, aimed at quantifying the effects of GrIS mass balance changes on current and future AMOC variability and predictability including uncertainty estimates. Realistic meltwater scenarios will be developed based on a new approximation of GrIS surface mass balance changes. The meltwater will be distributed to the ocean along the Greenland coast using a realistic runoff scheme. The range of meltwater scenarios will consider uncertainties associated with estimating future mass balance changes. Different state-of-the-science climate models will be forced with these scenarios in addition to standard radiative forcing in order to quantify the AMOC response to warming and meltwater input as well as the uncertainty of model AMOC sensitivities to the imposed forcings. Probabilistic AMOC projections will be computed based on the multi-model ensemble. Simulations with an interactive scheme of GrIS mass balance changes will be used to quantify the effect of ice sheet – ocean interactions on AMOC variability and predictability on decadal to centennial time scales. The model experiments will be carefully analyzed in order to understand responses and model differences. The probability of an AMOC shutdown in the coming two centuries will be quantified. The project will lead to international collaboration between scientists at different modeling centers and a new collaboration between global climate modelers and an expert on observations and detailed mass balance modeling of the GrIS.

Relevance to NOAA’s Long Term Goal of Climate Adaptation and Mitigation: Scientific understanding of the interactions between the cryosphere and the ocean will be advanced through realistic modeling of feedbacks between the GrIS and the AMOC. The combined potential impacts of global warming and melting of the GrIS on the AMOC will be assessed on decadal to centennial time scales. The project will lead to useful predictions of likely climate impacts including associated uncertainties, which can support mitigation and adaptation choices by decision makers. The PIs are actively engaged in education and outreach activities that will continue to improve public climate literacy. Results of this project will be published in the peer reviewed literature and disseminated as broadly as possible, e.g. through press releases via Oregon State University’s News and Research Communications office and interviews with reporters.

Understanding Equatorial Pacific Climate Processes via Hierarchical Coupled Modeling

Principal Investigator(s): Andrew T. Wittenberg, Brandon Reichl, Fanrong Zeng (NOAA/GFDL), Feiyu Lu, Alistair Adcroft (Princeton/AOS/CIMES)

Year Initially Funded: 2022

Program (s): Climate Variability & Predictability

Competition: Observation and Modeling Studies in Support of Tropical Pacific Process Studies, Pre-Field-II

Award Number: GC22-207 | View Publications on Google Scholar

Coupled GCMs (CGCMs) exhibit systematic errors in the climate of the tropical Pacific, including an equatorial cold tongue (ECT) that is too strong and too far west, and an ENSO with incorrect behavior and teleconnections. These biases limit climate forecast skill and confidence in future climate projections. The modeling community has identified deficiencies in ECT air-sea interactions, upwelling, and mixing as key contributors to emergent CGCM biases, citing a lack of detailed observations as a major factor. To address this, TPOS 2020 aims to enhance observations of upper-ocean and air-sea processes in the tropical Pacific, especially in the ECT region as part of the PUMP process study. TPOS 2020 has specifically requested hierarchical modeling to assess simulation capabilities, attribute biases to underlying processes, and refine observing strategies. A coupled approach is needed to assess how biases and air-sea feedbacks interact in models. Thus we propose using a hierarchy of GFDL CGCMs and ocean models with varying resolutions, complexity, and observational constraints, to identify links among emergent biases and processes in the ECT, and refine observing strategies to improve model simulations, reanalyses, and outlooks. Our project builds upon recent field programs, ocean model studies, diagnostic frameworks, and research that illuminate how ECT biases interact with climate variations and climate change in models. We intend to leverage the latest modeling, reanalysis, and forecast systems developed by GFDL to support the NMME and CMIP6. By focusing on ECT processes, air-sea coupling, and model resolution and parameterizations, the proposed studies will lend critical insights into strategies for observing the processes relevant to the ECT, and for improving NOAA’s models, products, and science.

Understanding Tropical Pacific Biases in Climate Simulations and Initialized Predictions

Principal Investigator(s): Andrew Wittenberg, NOAA/GFDL; Gabriel Vecchi, NOAA/GFDL; Tom Delworth, NOAA/GFDL; Yan Xue, NCEP/CPC; Arun Kumar, NCEP/CPC;

Year Initially Funded: 2014

Program (s): Climate Variability and Predictability

Competition: Improved Understanding of Tropical Pacific Processes, Biases, and Climatology

Award Number: GC14-250a | View Publications on Google Scholar

We propose a collaborative study between GFDL and NCEP, to advance understanding, simulation, and forecasting of tropical Pacific climate and its variability. Motivated by the central role that the tropical Pacific plays in climate variability worldwide -- in particular via the El Niño / Southern Oscillation (ENSO) -- there is an urgent need to advance mechanistic understanding of the tropical Pacific climatology and its impacts on climate variability, and to improve the coupled general circulation models (CGCMs) upon which society relies for seasonal-to-interannual (SI) forecasts and decadal-to-centennial predictions and projections. A unique strength of this proposal is close coordination between two of NOAA’s premier institutions for simulation, assimilation, and prediction of tropical Pacific climate and ENSO. In particular, a critical aspect of the proposed work is the development of common metrics, and a coordinated design and analysis of focused simulation and forecast experiments leveraging next generation models. This coordination will facilitate assessment of the robustness of the model results and underlying mechanisms, to accelerate improvements in NOAA’s SI simulation and prediction capabilities. Our goals are to (1) diagnose the spatiotemporal structure of tropical Pacific climatological biases in GFDL’s and NCEP’s coupled simulations, reanalysis systems, and forecasts; (2) identify similarities and differences among GFDL’s and NCEP’s model biases, and understand how differences can be linked to model parameterizations, assimilation methods, and observational inputs; (3) understand the processes which seed and amplify tropical Pacific biases; (4) assess how these biases affect the simulation and prediction of climate fluctuations; and (5) develop methods to mitigate these biases and their impacts on forecast skill. We will use our findings to evaluate existing hypotheses for the emergence of tropical Pacific biases, and to assess the applicability of our results to the broader set of community models and forecasts, including those available from the CMIP5 and NMME projects.

Relevance: The proposed work is highly relevant to the NOAA CPO. We seek to improve scientific understanding and prediction of the climate system, by evaluating and advancing methodologies used for simulations and forecasts. We directly address several objectives of NOAA’s Next Generation Strategic Plan (NGSP), including (1) Improved scientific understanding of the changing climate system and its impacts, by elucidating the causes and effects of simulation biases, and advancing climate modeling, predictions, and projections; (2) An integrated environmental modeling system, by advancing fundamental climate research and transitioning it toward NOAA’s production of seasonal forecasts, by coordinating within NOAA to enhance the accuracy of global models and predictions, and by evaluating and optimizing NOAA’s investments in observation and monitoring through the use of models; and (4) A climate-literate public that understands its vulnerabilities to climate, by elucidating the strengths and limitations of climate information affected by simulation biases. Relevance to the Competition: This proposal directly addresses the ESS CVP solicitation. The analysis and multimodel experimentation will focus on understanding tropical Pacific biases in two of NOAA’s leading coupled GCMs, which are widely used for climate simulation, reanalysis, and predictions. The work will leverage nearly all of the methods suggested in the proposal call, including advanced physical metrics, reduced-model experiments, and short-term forecasts, to diagnose the sources and amplifiers of model biases.

Improved Understanding of air-sea interaction processes and biases in the Tropical Western Pacific using observation sensitivity experiments and global forecast models

Principal Investigator(s): Aneesh Subramanian (CU Boulder/Formerly Scripps); Co-PIs: Matthew Mazloff (Scripps), Kris Karnauskas (CU Boulder), Charlotte DeMott (Colorado State University)

Year Initially Funded: 2018

Program (s): Climate Variability & Predictability

Competition: Pre-Field Modeling Studies in Support of TPOS Process Studies, a Component of TPOS 2020

Award Number: NA18OAR4310405, NA18OAR4310406, NA18OAR4310407 | View Publications on Google Scholar

We propose to determine physical mechanisms governing air-sea interactions in the tropical west Pacific at the eastern edge of the warm pool by isolating coupled feedback processes through analyses of short-term coupled and uncoupled forecasts. Climate model forecasts of the Madden–Julian Oscillation (MJO) and El Niño–Southern Oscillation (ENSO) experience a systematic climate drift resulting in biases of the modeled tropical western Pacific climatology. Global models tend to have an excess rainfall in the warm pool region and a deficiency in rainfall at the eastern edge of the warm pool. We propose to increase understanding of the dynamics and thermodynamics in the region by utilizing the Community Earth System Model (CESM) global runs as well as high-resolution Massachusetts Institute of Technology general circulation model (MITgcm) regional uncoupled simulations. Studying coupled vs uncoupled forecasts initialized with different ocean reanalysis products reveals the impact of ocean data assimilation on forecast error growth in the Tropical West Pacific region. The European Centre for Medium-Range Weather Forecasts (ECMWF) has recently completed several observation sensitivity experiments (OSE) ocean analyses by individually assimilating different ocean observation platforms (Argo, moorings, satellite, and others) into ocean analyses state estimates. Initializing our coupled forecasts from these OSE experiments will show the impact of different ocean observations on forecasts in the Tropical Pacific region. The PI (Subramanian) collaborates closely with Dr. Magdalena Balmaseda (ECMWF) who has given permission to use these OSE solutions. The proposed work will inform the role of forecast sensitivity to ocean state and air-sea feedbacks in the warm pool eastern edge region. Also the experiments with different ocean initializations will show the impact of various ocean observation platforms in constraining regional biases. The proposed analyses will help prioritize process study field campaigns and ocean observation platforms to best constrain modeling and parameterization development efforts. Analyzing air-sea interactions and the oceanic mixed layer heat and salt budgets in the model forecasts and in the reanalyses fields will reveal discrepancies in components of the budgets. This budget and flux analysis will yield a process-based understanding of the regional mixed layer, barrier layer, and MJO dynamics, feedbacks, and sensitivities. This research will identify the physical processes that lead to the mean and intraseasonal variability biases in the Tropical West Pacific and, more specifically, the key biases controlling MJO and ENSO background states. This understanding prioritizes process studies and observational field campaigns in the region as a part of TPOS 2020 on which processes to prioritize for observations. The work will also inform parameterization improvements for use in CESM for real-time forecasts of the climate-scale processes in the tropical Pacific.

Optimizing coupled boundary layer process studies in the tropical Pacific using high resolution models and in situ observations

Principal Investigator(s): Aneesh Subramanian, Kris Karnauskas (University of Colorado - Boulder), Charlotte DeMott (Colorado State University), Janet Sprintall (University of Californina - San Diego)

Year Initially Funded: 2022

Program (s): Climate Variability & Predictability

Competition: Observation and Modeling Studies in Support of Tropical Pacific Process Studies, Pre-Field-II

Award Number: NA22OAR4310599 NA22OAR4310600 NA22OAR4310601 | View Publications on Google Scholar

We propose to identify and study the physical mechanisms that play a key role in the evolution of the coupled boundary layer and air-sea interaction in the tropical west Pacific region (eastern edge of the warm pool [WPEE]). We will identify optimal strategies to observe these processes by isolating the coupled and uncoupled processes using short-term high resolution coupled and uncoupled regional model experiments and observing system simulation experiments (OSSEs). Current forecasts of the MJO and ENSO experience a systematic error (climate drift) that results in sustained biases of the model tropical western Pacific climatology. Salt-stratified barrier layers are persistent in the warm-fresh pool of the western Pacific. Correct modeling of the presence, location, and thickness of the barrier layer in the WPEE is critical for getting coupled air-sea processes right on MJO and ENSO time scales. This is because barrier layers can mediate the intensity of SST-wind-precipitation coupling in the region by inhibiting entrainment of cooler water from below and trapping solar radiation and wind momentum into the thin surface layer. This changing background state redefines the anomalous state, which is the target for subseasonal and interannual forecasts. The time scale over which this error develops depends on the model framework and the physical parameterizations. We propose to identify key processes and structures/characteristics that need increased observations (and at what temporal, horizontal, and vertical scales) to help improve our simulation of the coupled boundary layer in the region. Some of the processes we will focus on are: ● Barrier layer formation mechanisms (tilting, advection, stretching, buoyancy production vs shear-driven mixing) and their time/space evolution ● Understanding momentum, heat, and salinity budgets in the WPEE ● Coupled air-sea fluxes (including convection) east/west of SST front at the WPEE. We will first survey existing observations and reanalyses to compute statistical analyses of the different time periods and air-sea interaction regimes (e.g. wind and precipitation conditions, subsurface oceanic stratification, etc), to identify the optimal conditions under which to observe the processes of interest. We will then perform analysis of the CMIP6 models and observation sensitivity experiments using the ECMWF Forecast System to study these regimes of interest in the WPEE region and focus on the processes of interest. We will then configure and run a high resolution (~10 km) and very high resolution (~1 km) nested coupled model in the Tropical Pacific basin to sample (OSSE) the region just as an observationally-based process field campaign would with virtual observational assets. The proposed activity will help to address fundamental questions at the heart of the CVP call. Where do we need to know the ocean vertical structure versus being able to rely on surface conditions measured by satellites? Where do we need the highest density of Argo floats and gliders (that provide stratification) to detect barrier layers? We will work closely with the rest of the NOAA CVP and TPOS process study teams to utilize the tools we develop and optimize the design of the process study for success.

A Nudging and Ensemble Forecasting Approach to Identify and Correct Tropical Pacific Bias-Producing Processes in CESM

Principal Investigator(s): Aneesh Subramanian, Regents of the University of California; Art Miller, Regents of the University of California

Year Initially Funded: 2014

Program (s): Climate Variability and Predictability

Competition: Improved Understanding of Tropical Pacific Processes, Biases, and Climatology

Award Number: NA14OAR4310276 | View Publications on Google Scholar

Current short-term tropical climate forecasts (e.g, of the Madden Julian Oscillation (MJO) and of El Niño/Southern Oscillation (ENSO) events) experience both a systematic error (climate drift) that results in sustained biases of the model tropical climatology and an error in representing the space-time scales of the transients (e.g., phase speed errors, etc.) We propose to identify the physical mechanisms that lead to the seasonal biases in the tropical Pacific by isolating the parameters and parameterizations that influence the development of biases in short-term climate forecasts. Our overarching scientific objective is to identify, explain, and correct the climate biases in the Pacific ocean that occur in the Community Earth System Model (CESM). We are currently using the Community Atmospheric Model (CAM3) in MJO forecast experiments and tests of convective parameterization improvements. We propose to extend these MJO forecast studies to include (a) the fully coupled CESM system, and (b) ENSO timescale forecasts.

We plan to study the spatiotemporal structures of bias development in CESM forecasts, launched from numerous initial states and during which random ENSO and MJO events occur, to determine the relative importance of poor mean-state representation versus the integrated impacts of the transient flows. This bias development will be studied as a function of season to account for significant changes in the background state of the coupled oceanatmosphere system in the tropical Pacific. We will also seek to ascribe these effects to wellknown physical processes for the specific climate modes of variability. We will test the sensitivity of the bias development to changes in coupled model resolution and model parameter selection. We will also implement nudging experiments (towards observations) to pinpoint where the worst parts of the biases develop apart from the nudged variables.

We expect this research to result in identification of the physical processes that lead to the mean biases in the model system and an improvement in parameterizations used in CESM and CAM for forecasts of the climate-scale processes in the tropical Pacific.

This proposal contributes to the CVP component of the NOAA ESS Program by attempting to improve our understanding of the processes contributing to tropical Pacific biases in global climate models (CESM, in this case). Specifically, our work involves (i) short-term forecast experiments, from weeks to a year, to isolate the time scales of bias development and the responsible processes, (ii) development of metrics for coupled GCMs that help to elucidate the main processes contributing to biases, (iii) atmosphere-only and ocean-only models to isolate the sources and amplifiers of biases, and (iv) intercomparison of model parameterizations within CESM. Our overall research will thereby contribute significantly to NOAA’s Next Generation Strategic Plan by improving our scientific understanding of the climate system that will result in better identifying potential climate impacts.

Developing a framework for a field campaign in the cold tongue: Analysis of Pacific Upwelling and Mixing Physics from models and observations

Principal Investigator(s): Anna-Lena Deppenmeier, Deepak A. Cherian, Frank O. Bryan (University Corporation for Atmospheric Research - UCAR), LuAnne Thompson (University of Washington), William S. Kessler (NOAA/PMEL)

Year Initially Funded: 2022

Program (s): Climate Variability & Predictability

Competition: Observation and Modeling Studies in Support of Tropical Pacific Process Studies, Pre-Field-II

Award Number: NA22OAR4310595 NA22OAR4310596 | View Publications on Google Scholar

The intense oceanic heat uptake and air-sea coupling of the eastern equatorial Pacific cold tongue are enabled and maintained by efficient, turbulence-driven communication between the surface and the shallow thermocline. The cold tongue is dynamically special: the shoaling thermocline and resulting strong shear between the westward surface current and the shallow eastward equatorial undercurrent (EUC) result in flow that is persistently susceptible to shear instability below the mixed layer (marginally unstable flow). Shear turbulence is triggered every night, transporting heat from the ocean surface to the upper flanks of the EUC. This shear turbulence exposes the upper thermocline as a sink of heat (and a source of carbon). The former cools SST resulting in a large flux of heat from the atmosphere into the ocean. Our previous work with high resolution models demonstrates that the long-term mean ocean mixing and strong water mass transformation is concentrated in a narrow eastern equatorial zone between approximately 2 S and 2 N above the EUC, where upwelling brings the thermocline close to the surface. On shorter time scales, intense mixing exists outside this narrow band: flow in the cold cusps of simulated Tropical Instability Waves is marginally unstable and mixing can extend as far north as 5 N. These results demand deeper investigation of the near-equatorial marginally unstable flow, its spatial extent, temporal variability, and connection to the background near-equatorial circulation. In this response to the competition CVP: Observation and Modeling Studies in Support of Tropical Pacific Process Studies, Pre-Field-II: 2943817 we propose research to advance our understanding of upwelling and mixing physics in the cold tongue. Our motivating questions are: What is the influence of variations in near equatorial mixing on the geography of air-sea fluxes and large scale features such as the tropical cells? Which macroscale phenomena modulate near-equatorial mixing and water mass transformation? What sampling strategies will capture the essential dynamics of these interactions in the context of both the PUMP field campaign and long-term TPOS backbone array? To address these questions we will: Elucidate and diagnose oceanic processes, and scales of those processes, that control mixing and upwelling in the eastern tropical Pacific thermocline; Characterize the spatial and temporal variability of shear, stratification, and mixing high-resolution models, large eddy simulations, and observations; Perform Observing System Simulation Experiments to test the proposed frameworks; Construct testable hypotheses and associated sampling strategies for a potential PUMP field experiment to constrain equatorial upwelling and mixing that will ultimately provide guidance for improvement of model parameterizations; Develop indirect and bulk indicators of diabatic mixing processes that can be inferred from routinely observed quantities. The outcome of this effort will further our scientific understanding of vertical exchange in the cold tongue and facilitate the interpretation of observations from a future PUMP field campaign and optimally utilize the backbone array. Ultimately, observations of these processes will serve to evaluate, constrain and guide the development of ocean models.

Understanding drivers and impacts of CGCM biases in representing the decadal variability of Labrador Sea convection

Principal Investigator(s): Annalisa Bracco (Georgia Tech), Takamitsu Ito (Georgia Tech)

Year Initially Funded: 2016

Program (s): Climate Variability and Predictability

Competition: AMOC-Climate Linkages in NA/SA

Award Number: NA16OAR4310173 | View Publications on Google Scholar

The Labrador Sea (LS) is one of the few regions in the world ocean where deep convection occurs. The intense air-sea interaction drives the convective mixing and the site acts as a window through which anthropogenic carbon is sequestered into the interior ocean. Recent work highlights that buoyancy forcing over the Labrador Sea is key in controlling the Atlantic Meridional Overturning Circulation (AMOC) and that AMOC inter-annual signals are closely related to the variability of the Labrador Sea convection. Historic observations collected over the past 60 years show that the LS convective activity undergoes dramatic interannual-to-decadal variability and –within the limitation of the available measurements – no statistically significant trend. A model integration performed using a regional ocean model (ROMS, Regional Oceanic Modeling System) run at 5km horizontal resolution over the LS can reproduce the observed variability. However, coupled general circulation models (CGCMs) from the Coupled Model  Intercomparison Project Phase 5 (CMIP5) are not yet capable of representing the extent and  statistical properties of the LS convection, while often displaying a weakening trend for the past  50 years. Model biases hamper the representation of the AMOC and of the inventories of dissolved inorganic carbon, and limit our ability to project their future changes.  The overarching objectives of this project are to diagnose the sources of CGCMs biases in the LS focusing on a subset of CMIP5 runs and to quantify the impacts of those biases on the representation of carbon uptake and inventories in the basin. They will be achieved through a sensitivity study to be performed using regional ocean-only ROMS simulations covering most of the North Atlantic forced by momentum, heat and freshwater fluxes, and/or boundary conditions from the CMIP5 runs.
This project will establish cause-effect linkages between the representation of mesoscale processes, of the atmospheric forcing fields, and of the gyre circulation, and the (modeled) Labrador Sea circulation, its variability and carbon uptake characteristics.  The regional simulations will include an ocean biogeochemical and carbon cycling module. The interpretation of all model analysis will be aided by careful comparisons with shipboard and Argo measurements in the Labrador Sea, and along 53N. In this regard we will build upon our ongoing collaboration with Dr I. Yashayeav at the Bedford Institute of Oceanography. This project will contribute a better understanding of the potential predictability of Labrador Sea convection and of the natural and anthropogenically forced variability of the AMOC.
This proposal addresses the objective of the NOAA funding opportunity, CVP AMOC-Climate Linkages in the North and/or South Atlantic (NOAA-OAR-CPO-2016-2004413) to ‘refine the  current scientific understanding of the AMOC state, variability and change’ by focusing on the  interannual and decadal variability for the LS branch. The proposed work contributes to three  priorities identified in the US AMOC 2014 report and advances the NOAA’s Next-Generation  Strategic Plan to ‘improve scientific understanding of the changing climate system by diagnosing  the physical and biogeochemical biases in the CGCMs that are used in the future prediction and  projections by the Intergovernmental Panel on Climate Change’.

Predictability of Multi-Decadal Climate Variations in the Mediterranean "Hot Spot"

Principal Investigator(s): Annarita Mariotti, University of Maryland

Year Initially Funded: 2010

Program (s): Climate Variability and Predictability


Award Number: | View Publications on Google Scholar

The Mediterranean region has been identified as a primary climate change “Hot Spot”, with a greenhouse gas “forced” signal projected to emerge already early in the 21st century. Natural multi-decadal fluctuations will contribute to define the climate variations which will be observed in the next few decades. The forced climate response and a linkage with the Atlantic Multi-decadal Oscillation (AMO) suggested by various studies, are both potential sources of regional predictability. A careful evaluation of the regional decadal predictive potential and of current prediction capability is urgently needed to plan for climate adaptation. 

The goal of this work is to assess the degree of decadal predictability of climate anomalies in the Mediterranean region. Research will test the hypothesis that “There exists significant decadal predictability of climate anomalies in the Mediterranean region resulting from external forcings and AMO-related variability”. The proposed research has the following objectives: 1) assess the degree of predictability of past decadal climate variations in the Mediterranean region by evaluating the role of AMO-related variability and the externally forced response 2) assess the skill of CMIP5-class decadal prediction systems to hindcast past decadal Mediterranean climate anomalies and evaluate future decadal predictions. Research tasks include observational-model based analyses of the AMO-Mediterranean linkage and of CMIP5 model performance; an examination of sources of regional predictability; an evaluation of CMIP5 hindcasts prediction experiments over the Mediterranean, and of decadal predictions of future regional climate anomalies. 

Work will contribute to CMIP5-related research initiatives to address decadal variability/predictability/prediction, building understanding on decadal predictability and evaluating CMIP5 decadal prediction systems taking the Mediterranean as a test-bed. This proposal addresses CVP’s FY 2010 “Decadal Climate Predictability and Prediction” priorities by performing necessary underpinning work to meet the challenge facing NOAA and the international climate community to develop Climate Services. 

Oceanic Mechanisms of Tropical Pacific Climate Variability Involving the Subtropical-Tropical Cells (STCs)

Principal Investigator(s): Antonietta Capotondi, Prashant D. Sardeshmukh (NOAA/ESRL/PSD)

Year Initially Funded: 2020

Program (s): Climate Variability & Predictability

Competition: Decadal Climate Variability and Predictability

Award Number: GC20-202 | View Publications on Google Scholar

Tropical Pacific decadal variability (TPDV) plays an important role in the global climate, as evident from its influence on the recent slowdown of the global surface temperature trend. Decadal variations of tropical Pacific background conditions also affect the amplitude, frequency, and spatial pattern of El Niño Southern Oscillation (ENSO) events on inter-annual timescales, whose global impacts can be sensitive to the distinctive evolution and structure of individual events. For both of these reasons it is important to assess the predictability of TPDV through a better understanding of its underlying mechanisms. Despite extensive research, however, a clear understanding of those mechanisms remains elusive. Some studies have suggested that TPDV may originate purely by chance, while others have emphasized the role of slow oceanic adjustment processes and their possible feedbacks on the atmosphere. Such processes involve upper-oceanic meridional overturning circulations in both hemispheres known as Subtropical-Tropical Cells (STCs), as well as oceanic Rossby waves that mediate the STC adjustment and the evolution and structure of tropical Pacific heat content. A connection between STC strength and equatorial SST anomalies has been shown in several studies using relatively short observational and model datasets. However, many questions remain unanswered. The primary goal of the proposed research is to elucidate the role of oceanic dynamical processes in TPDV using a combination of observations, oceanic and coupled atmosphere-ocean reanalysis products, and model outputs from the Climate Model Inter-comparison Project phase 6 (CMIP6). Our specific objectives are 1) to examine the role of the northern and southern STCs and oceanic Rossby waves in altering the tropical upper-oceanic heat content and tropical SSTs at decadal timescales, and to assess the nature of the wind anomalies forcing these processes; 2) to evaluate the representation of TPDV in pre-industrial and historical simulations of the CMIP6 models; and 3) to use the CMIP6 future scenario simulations to examine projected changes in TPDV and its associated processes. The proposed research will directly address the first priority area of the competition: “Investigation of mechanisms that govern variability of the coupled climate system and its predictability on the interannual to multi-decadal timescales within long-term observation and/or model data (such as, CMIP6)” by examining the mechanisms of decadal/multi-decadal variability in the tropical Pacific, the low-frequency modulation of interannual variability, and the degree of predictability associated with those mechanisms.

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