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Shallow cumulus convection in the Tropical Atlantic Ocean: Controls, responses, and mechanisms

Principal Investigator(s): Graham Feingold (NOAA/ESRL/CSD); Jan Kazil (CU-CIRES); Takanobu Yamaguchi (CU-CIRES)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: GC19-303 | View Publications on Google Scholar

Differences in the representation of shallow cumulus convection and cloudiness are a leading contribution to diversity in climate model sensitivity and climate projections. We propose to use numerical modeling of trade-wind cumulus from large eddy simulations to regional modeling, analysis of field observations, satellite data, and of reanalysis products to address the coupling between convective mixing, surface turbulent fluxes, and low-cloud radiative effects in largescale subsidence regimes. The modeling will be tightly integrated with the Atlantic Trade-wind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC, US) and the Elucidating the Role of Clouds-Circulation Coupling in Climate (EUREC4A, Europe) Ocean-Atmosphere field campaigns. We will examine the controls on the properties, statistics, and organization of shallow cumulus convection and cloudiness, and its response to ocean and atmosphere mean state and variability. Emphasis will be placed on processes that are unresolved or unrepresented in climate models and which contribute to diversity and biases in climate simulations and model-derived climate sensitivity. The objectives are: • Quantification of the mean state and statistical properties of shallow cumulus convection in response to atmospheric and oceanic mean state, and atmospheric and oceanic spatiotemporal variability • Quantification and characterization of mesoscale organization, its response to oceanic and atmospheric mean state and variability, and its role for the properties of trade cumulus convection and cloudiness • Characterization of feedback mechanisms between the atmosphere and the ocean that codetermine ocean-atmosphere interactions and the properties of trade cumulus convection and cloudiness Modeling will be carried out in close concert with the European and US assets to be brought to the field: aircraft observations (the NOAA P-3 and NOAA G-IV, the French ATR-42 and the German HALO), shipborne measurements (the NOAA R/V Ronald H. Brown and up to three European ships), and satellite remote sensing. The proposed work will further NOAA's long-term climate research goals and the goals of the NOAA CVP program by enhancing the understanding of the climate system and its predictability in a number of ways. First, it will elucidate our fundamental understanding of the trade-wind cumulus system by focusing on the meteorological/ocean surface factors that control cloud field properties (e.g. cloud fraction, condensate, and precipitation) through comprehensive modeling and observations at a broad range of scales (10s to 100s of km). Second, the extent to which variance in these factors at the sub GCM grid-scale affects these cloud field properties will reveal the model grid mesh required to adequately resolve them. Third, the model output and analysis of observations will together provide a wealth of data to inform development of GCM subgrid cloud and precipitation schemes for years to come.

Upper-ocean salinity variability in the northwestern tropical Atlantic and its interactions with SST and winds

Principal Investigator(s): Gregory Foltz (NOAA/AOML), Denis Volkov (NOAA/AOML); Christophersen (NOAA/AOML) Collaborators: Rick Lumpkin (NOAA/AOML), Renellys Perez (NOAA/AOML), Shenfu Dong (NOAA/AOML), Gustavo Goni (NOAA/AOML)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: GC19-304 | View Publications on Google Scholar

Two important topics in need of further research are (1) the impact of upper-ocean salinity on stratification, mixing, and sea surface temperature (SST), and (2) interactions between ocean mesoscale eddies and the atmosphere. The northwestern tropical Atlantic (NTA) is an advantageous place to address these questions because it experiences strong eddy activity and pronounced surface freshening from Amazon River outflow. Furthermore, during boreal winter, shallow cumulus clouds are prevalent in the NTA and are affected by the underlying SST. The details of how these clouds form and interact with the ocean are not well known, contributing to significant uncertainty in climate models’ radiation budgets. Previous research has shown that, on average, six large anticyclonic rings translate northward in the NTA each year after separating from the North Brazil Current (NBC) retroflection. Though the volume transport associated with the rings has been quantified, the upper-ocean temperature and salinity structures are not well known. It is also unclear how the rings affect near-surface winds and heat fluxes. It has been established that salinity contributes significantly to upper-ocean stratification in the NTA during boreal winter, but there is debate on the impact of salinity on SST in this region. The uncertainties are compounded by strong mesoscale salinity variability from NBC rings. These gaps in knowledge limit our understanding of ocean-atmosphere coupling and cloud variability in the NTA. This proposal aims to improve our understanding of eddy variability and ocean atmosphere interactions in the NTA through the deployment of a set of unique surface drifting buoys, combined with analysis of historical in situ and satellite data and one-dimensional ocean model experiments. The drifting buoys will provide new and valuable information on the temperature and salinity structure in the upper 10 m of the ocean, including the diurnal cycle and the conditions within and outside of rings and eddies. Wind velocity measurements from the drifters will be used to diagnose changes in upper-ocean temperature and salinity structure and potential eddy-atmosphere coupling. Ocean model experiments will provide deeper process oriented insight into the impacts of salinity, winds, and surface heat fluxes on upper-ocean mixing and SST. The proposed work is directly related to Competition 2 of NOAA/CPO’s CVP announcement, which seeks studies focused on observing, understanding, and/or process modeling of upper ocean processes and air-sea interactions in the Northwest Tropical Atlantic as part of the ATOMIC/EUREC4A-OA field campaigns. The proposed measurements and analysis will also advance our understanding of upper ocean processes (diurnal cycle and evolution of upper-ocean temperature and salinity structure), ocean boundary layers, and mesoscale ocean eddies, which is a specific goal of the proposal call. More broadly, our proposed work aligns well with the mission of the CVP program, which is to support research that enhances our process level understanding of the climate system through observation, modeling, analysis, and field studies.

A Global Model Investigation of MJO Initiation for DYNAMO

Principal Investigator(s): Guang Zhang, Scripps Institution of Oceanography

Year Initially Funded: 2011

Program (s): Climate Variability and Predictability


Award Number: | View Publications on Google Scholar

The DYNAMO field campaign in the Indian Ocean provides an unprecedented opportunity to study MJO initiation. In this project, the PI proposes to investigate the MJO initiation in the Indian Ocean using the NCAR CAM3 and the DYNAMO observations. The objective is to improve MJO simulation, and ultimately MJO prediction using global models. As part of the DYNAMO modeling effort, the project aims to answer the following scientific questions relevant to Hypotheses I and II in the DYNAMO Science Planning Overview (SPO) document:

I. What are the factors determining the initiation of MJO in the Indian Ocean?
II. How does the cloud population interact with the MJO circulation during MJO initiation? Can the NCAR CAM3 reproduce the observed cloud population?

The basic research tools used in this work are the NCAR CAM3 and the improved Zhang-McFarlane convection scheme. The data used for model evaluation and improvement will be DYNAMO field observations from sounding array, radar and satellites, ECMWF reanalyses products, and other data assembled by the Year of Tropical Convection (YOTC) project. The combination of model and observations will allow us to test new ideas using models and evaluate them using observations. To answer the above questions, we will perform a series of simulations using the CAM3 and its single column version in both prediction mode and the traditional climate simulation mode. Simulation tests will be conducted to determine what factors affect the MJO initiation the most. In particular, shallow convection preconditioning, convective sensitivity to environmental moisture through lateral entrainment, sea surface temperature and surface evaporation, among others, are deemed critical to MJO initiation. We will investigate each of them in the proposed research. The model output will be compared with DYNAMO observations and reanalyses products. For each observed and simulated MJO, budgets of heat and moisture will be computed to determine the sources and sinks of moisture during different stages of MJO initiation over the Indian Ocean. The cloud population, as measured by cloud top heights and optical depth, during the MJO life cycle from model simulations and satellite observations will be compared and related to MJO circulation. We will also participate in the inter-model comparisons to identify sensitivity of different models to parameters in convection scheme.

Intellectual merit: MJO simulation is a challenging scientific problem in GCMs. Using an improved version of the convection scheme developed by the PI, the NCAR CAM3 can simulate MJOs realistically. Thus, the model can be used as a tool together with DYNAMO observations to understand MJO initiation in the Indian Ocean. The work will help improve the MJO simulation and prediction not only in CAM3, but also in other GCMs.

Broader impacts: Poor MJO simulation is a well recognized problem in many GCMs. It negatively impacts the model development efforts in the global modeling community, and affects the simulation of other climate systems. This work will have impacts beyond the MJO dynamics and simulation. MJO simulation can be used as a metric to evaluate model performance.

Sea-Ice Variability and the North Atlantic Oscillation on Interannual to Decadal Timescales

Principal Investigator(s): Gudrun Magnusdottir, University of California - Irvine

Year Initially Funded: 2009

Program (s): Climate Variability and Predictability


Award Number: | View Publications on Google Scholar

The North Atlantic Oscillation/Northern Annular Mode (NAO/NAM, hereafter NAO) is the most important global mode of atmospheric variability in the northern extratropics especially in winter. It is expressed as a seesaw in mass between high- and mid to subtropical latitudes. This relation is especially dominant in the North Atlantic basin. Sea-ice concentration is to first order forced by the atmosphere and observations show that sea-ice variability in the North Atlantic sector of the Arctic is closely tied to the NAO. The primary mode of variability in sea ice is a dipole with nodes in the Labrador and Barents Seas, respectively. A positive NAO is associated with increased sea-ice concentration in the Labrador Sea from NAO induced wind forcing and decreased sea-ice concentration in the Barents Sea from NAO-induced, positive, oceanic heat-flux anomalies. 

The NAO was in its strong positive polarity from the 1960s to the mid 1990s and during this time sea-ice concentrations decreased in the Barents Sea and increased in the Labrador Sea. When we asked the question in Atmosperic Global Climate Model (AGCM) simulations, is there a feedback from this spatial pattern of change in sea ice back onto the NAO (or atmospheric circulation), we found a clear negative feedback in the equilibrium winter response. We have recently examined the transient response to this sea-ice forcing to determine what processes control the evolution to a negative NAO. We found that the initial modest circulation response from the change in surface fluxes allows a changed configuration of Rossby wave breaking and it is the latter effect that leads to the more prominent and larger scale (equilibrium) response of a negative NAO. Thus internal (or natural) variability indirectly sets the stage for the prominent response to a changed sea ice distribution. It is the interaction of the short time-scale internal variability with the forced initial response that sets the stage for the evolution of the amplified large-scale change. 

We are now entering an unchartered era in sea-ice variability. In addition to the NAO related mode of sea-ice variability (the Labrador-Barents Sea dipole), rapid anthropogenic sea-ice loss, even in winter, is an even more prominent mode of variability. Sea-ice observations are beginning to show this effect, but the clearest signature may be seen in climate model projections. Interestingly, the climate model projection show the NAO related dipole of variability as the second leading mode, the overall sea-ice decline is the first leading mode. 

In this research we seek to identify, understand and quantify the dynamical feedback processes between 1)the atmospheric circulation, 2)sea-ice concentrations and 3)the oceanic heat flux, from observations and a hierarchy of numerical models with the ultimate goal of facilitating prediction of North Atlantic climate on interannual to decadal timescales. The models range from linear stochastic equations linking the NAO index and sea-ice concentration, to AGCMs, to coupled (atmosphere, sea ice, ocean) climate models with a simplified ocean that allow for easier identification of processes, to output from fully coupled state of the art climate models. With coupled reanalysis products on the horizon, the research is timely and holds great potential in the quest for decadal prediction of climate. 

Extreme moisture transport (atmospheric rivers) into the Arctic and its effect on sea-ice concentration

Principal Investigator(s): Gudrun Magnusdottir, University of California, Irvine

Year Initially Funded: 2015

Program (s): Climate Variability and Predictability

Competition: Understanding Arctic Sea Ice Mechanisms and Predictability

Award Number: NA15OAR4310164 | View Publications on Google Scholar

Over recent decades the Arctic has warmed approximately twice as fast as the rest of the Northern Hemisphere. At the same time, Arctic sea-ice concentration has decreased rapidly, especially in September when sea ice in the Arctic reaches its lowest extent of the year. Interannual variability in the minimum sea ice extent is enormous, especially over the past decade that includes several years of record minimum coverage interspersed with other less extreme years. Satellite observations of sea ice concentrations go back to 1979.

This vast interannual variability is mostly driven by extratropical atmospheric dynamical processes both directly and indirectly, and modulated by slower ocean processes. Wind represents an important forcing of sea ice distribution that qualifies as direct forcing. Thermodynamical consequences of extratropical dynamical variability such as changes to the radiative surface fluxes due to increased moisture in the Arctic can in turn lead to important feedback processes that can quickly amplify the change. A recent study indicates that in years when there is a low Arctic sea-ice minimum in September there is an increase in moisture transport into the Arctic in the preceding spring. The increase in moisture leads to increased greenhouse effect that is thought to play an important role in initiating the melt in spring that will become an extensive area of melt in September. We hypothesize that the extreme moisture transport into the Arctic in the form of atmospheric rivers (ARs) during certain key parts of the year plays an important role in the extent of the sea-ice minimum that is reached each year, and overall in interannual variability of sea ice concentrations.

We propose to analyze the frequency and moisture flux of ARs in certain key areas of the Arctic in 35 years of reanalysis data, the time period of which overlaps with observations of sea-ice concentration. We will examine sea-ice concentration and surface fluxes following episodes of extreme moisture flux, as well as the large-scale flow because of the close association of ARs to Rossby wave breaking, a process that drives major climate patterns. We will carry out similar analysis for the archive of CMIP5 climate simulations, both historical runs and projections for the coming century under projected increases in greenhouse gases. We will test hypothesis regarding the role of ARs for Arctic sea ice concentration by running idealized Global Climate Model simulations.

The work is directly relevant to the opportunity in that it examines climate mechanisms that affect Arctic temperatures and variability in sea-ice concentration in observations and model simulations. This will lead to an improved scientific understanding of the changing climate system, which is a stated goal of NOAA’s Next Generation Strategic Plan.

Understanding and Improving GCM Simulations of MJO Initiation over the Tropical Indian Ocean using DYNAMO Field Observations

Principal Investigator(s): Hailan Wang, Science Systems and Applications Inc. (SSAI); Siegfried Schubert, NASA/GMAO; Leo Donner, NOAA/GFDL

Year Initially Funded: 2013

Program (s): Climate Variability and Predictability


Award Number: NA13OAR4310162 | View Publications on Google Scholar

Despite the numerous improvements made to General Circulation Models (GCMs) in recent years, current models continue to be deficient in simulating and predicting the Madden-Julian Oscillation (MJO), a leading tropical intraseasonal mode of variability that interacts with and influences a wide range of weather and climate phenomena. Particularly problematic is the simulation of the initial phase of the MJO over the tropical Indian Ocean ± a deficiency that limits both forecast skill and the ability to simulate a wide range of scale interactions linked to the MJO. The Dynamics of MJO (DYNAMO) field campaign, which provided in-situ observations over the central tropical Indian Ocean during the period October 1, 2011-March 31, 2012, will provide a unique opportunity to confront GCMs with in-situ observations, with the ultimate goal of improving GCM simulations and predictions of the MJO.

It is proposed to use in-situ observations collected during the DYNAMO field campaign and the NASA Goddard Earth Observing System Model, Version 5 (GEOS-5) model system, to better understand the key physical processes associated with the MJO initiation over the tropical Indian Ocean and identify the main model deficiencies in simulating the MJO initiation. First, we will use the latest GEOS-5 data assimilation system to produce the global high-resolution DYNAMO Reanalysis so as to place the DYNAMO in-situ observations in a global context. The DYNAMO Reanalysis will be analyzed to investigate the key physical processes associated with the MJO initiation over the tropical Indian Ocean, and assess the GEOS-5 Atmospheric GCM (AGCM) deficiencies through a detailed examination of the analysis increments that should largely reflect model bias. Second, we will perform a series of AGCM and coupled replay experiments, to investigate the relative roles of atmospheric processes, and the impact of air-sea interaction, for the MJO initiation over the tropical Indian Ocean. Third, a series of coupled MJO reforecasts will be performed to assess the contribution of the DYNAMO in-situ observations to an enhanced MJO forecast skill through improvements in atmospheric and oceanic initial conditions. The root cause(s) of GEOS-5 limited forecast skill will be assessed through in-depth case-study analyses of when and where in the early stages of the MJO life cycle the model begins to lose skill. Lastly, we will perform a series of GCM sensitivity experiments to investigate the model convective sensitivity to environmental moisture as well as to address model issues revealed in the above data diagnosis.

The above work with the GEOS-5 model will be coordinated with on-going modeling efforts at NOAA Geophysical Fluid Dynamics Laboratory (GFDL) that address the simulation of the MJO in the GFDL Atmospheric Model version 3 (AM3) and Coupled Model version 3 (CM3) models. It is anticipated that frequent interactions between Global Modeling and Assimilation Office (GMAO) and GFDL on lessons learned, as well as some joint model experimentation, will be key to achieving fundamental improvements that extend beyond any model-specific bias, and point to fundamental improvements in the representation of the MJO in both the GEOS-5 and GFDL GCMs.

The proposed work targets the focus area "Understanding and Improving Prediction of Tropical Convection using Results from the DYNAMO Field Campaign" solicited by FY 2013 NOAA Earth System Science (ESS) Program, and directly addresses the motivation and goal of the DYNAMO program. It will contribute to NOAA's long-term goal of climate adaptation and mitigation through "Improved scientific understanding of the changing climae system and its impacts".

Coupled ocean-atmosphere interaction mediated by ocean mesoscale eddies in the Northwest Tropical Atlantic Ocean

Principal Investigator(s): Hyodae Seo (WHOI); Carol Anne Clayson (WHOI)

Year Initially Funded: 2019

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Upper - Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean

Award Number: NA19OAR4310376 | View Publications on Google Scholar

The primary goal of the ATOMIC experiment is to improve understanding of ocean-atmosphere interaction in the presence of energetic ocean mesoscale variability in the northwest tropical Atlantic. A particular focus is on documenting the role of ocean mesoscale eddies and fronts in the surface fluxes of momentum, heat, and freshwater, and examining how the eddy-mediated air-sea fluxes relate to ocean boundary layer mixing, low-level clouds, and regional climate. We hypothesize that the mesoscale variations in the air-sea flux at sub-monthly and sub-100-200 km scales represent an essential part of the coupled boundary layer physics in the study region. However, spatially distributed measurements and dedicated high-resolution coupled model simulations do not coexist as yet to describe and quantify the eddy-mediated air-sea flux variability and its impacts. We propose a hierarchy of model simulations in tandem with other observational studies in support of the ATOMIC/EUREC4A to improve our process-level understanding of the physics of, and the factors influencing, the mesoscale variations in the air-sea fluxes. It will also provide a unique opportunity to explore their upscaling effects on the trade wind cumuli and large-scale regional climate. Our simulations will be based on the 3-D SCOAR regional coupled model (WRF-ROMS) and a 1-D implementation of the 3-D ocean model with various mixing schemes. The 1-D model simulations will primarily investigate the effects of background stratification modulated by mesoscale eddies and the resulting changes in the surface waves and air-sea fluxes on the ocean mixing and dissipation rate. The 3-D SCOAR model simulations will be run at 3 km resolutions both in the atmosphere and the ocean to explicitly resolve cumulus convection and ocean mesoscale variability. These fine-scale ocean and atmospheric fields will be coupled through the COARE bulk flux algorithm including any changes that may arise from other proposed ATOMIC research. The spatial-scale dependent effects of mesoscale eddies on the air-sea fluxes will be examined by our novel coupling technique, which filters out imprints of mesoscale eddies (SST and current) in surface fluxes. Finally, ensembles of 3-D coupled model simulations will be conducted with one-way and two-way nesting to explore the upscaling effects on the regional-scale ocean and atmospheric boundary layers. Coupled model simulations at the proposed fine spatial and temporal scales have not been conducted previously alongside observations with sufficient spatial and temporal detail to constrain and validate the model simulations. The proposed model simulations will allow for air-sea coupling at submonthly scales and sub-100-200 km scales to be quantified for the first time in the region. To guide the field experiments, various virtual sampling arrays with online budget calculations will be trialed to assess the efficacy for proposed sampling strategies. We expect that other science questions and new observational plans if they emerge can be addressed by our unique and flexible modeling plan. Improved physical understanding of mesoscale and frontal-scale ocean-atmosphere interactions is currently of significant interest to the science community. The proposed research will help improve climate model simulations at such scales and benefit the general public by helping to provide more reliable regional-scale predictions. The project will support a postdoc in physical oceanography and meteorology and offer various opportunities to mentor students from historically under-represented groups in the sciences through WHOI and other REU programs designed to promote diversity.

Exploiting coupled ocean-atmosphere-wave model simulations to identify observational requirements for air-sea interaction studies across the tropical Pacific

Principal Investigator(s): Hyodae Seo, Susan Wijffels (Woods Hole Oceanographic Institution - WHOI)

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: NA22OAR4310598 | View Publications on Google Scholar

The goal of the TPOS2020 project is to design an efficient and effective backbone observing system to better understand the processes in the tropical Pacific that are instrumental to the El Niño-Southern Oscillation (ENSO) and provide useful observational constraints for predictions. The process studies being planned in the western and eastern equatorial Pacific are intended to shed light on physical processes and guide the design and development of the TPOS. The strong sea surface salinity and temperature fronts marking the eastern edge of the warm pool and equatorial cold tongue represent dramatic regime transitions from the ocean-atmosphere-wave coupling perspective, where short space/time scale changes in the balance between the oceanic and atmospheric boundary layers present significant observational and modeling challenges. As recognized by the TPOS2020, the current tropical Pacific observing system is insufficient to characterize the transient and fine-scale nature of the ocean-atmosphere-wave interactions. This hampers our ability to understand the impacts on local and non-local large-scale drivers, such as Madden-Julian Oscillation (MJO) and ENSO. Most simulation and operational models exhibit difficulty simulating these processes due to inadequate spatial resolution and physical parameterizations. The biases in observations and models, in turn, impede developing and testing robust coupled data assimilation schemes for numerical weather prediction and extended-range prediction systems on subseasonal-to-seasonal and seasonal time-scales. We propose a pre-field modeling study to improve our process understanding and representation of air-sea flux and associated turbulent exchanges and dissipation in the oceanic and atmospheric boundary layers across the multiple TPOS regimes and to determine their dependence on varying ocean eddy and fronts, diurnal cycle, barrier layer, and surface wave conditions. A crucial element is to exploit extensive high-resolution, ocean-atmosphere-wave coupled model simulations, validated with existing in situ and satellite observations in the TPOS, to determine the simulation sensitivity to assumptions in the parameterized air-sea interaction and choices of model physics and resolution. Our combined model simulations and data analyses aim to provide specific and helpful information to the design of the process study and the TPOS observing system while also contributing to refinements of existing air-sea flux and turbulent mixing schemes to improve simulation and prediction models. Better resolved and represented air-sea interaction in the model will then be used to quantify the impacts on simulation skills of large-scale climate drivers such as MJO and ENSO. The project directly contributes to the most relevant priority areas of TPOS Process Studies and TPOS2020, and the NOAA's broad mission of improved environmental prediction by enhancing the predictability of the evolution of the Pacific climate system on seasonal to interannual time-scales. First, the project will examine the roles of surface waves, stratification and mixing, and eddies and fronts, the primary observational foci of the TPOS process studies. The refined model and improved process understanding will guide the design of a distributed array of in situ observations to improve space-time sampling. Secondly, it is of primary interest to TPOS to determine whether and how the improved representation of air-sea interaction improves the simulations of the critical large-scale variability such as MJO and ENSO. The enhanced mechanistic understanding of the upscaling effect will aid the improved extended-range and seasonal to multi-year predictions.

High-resolution tracer study of AMOC pathways and timescales

Principal Investigator(s): Igor Kamenkovich (University of Miami); Zulema Garraffo (I.M. Systems Group, Inc.); Avichal Mehra (NOAA/NCEP)

Year Initially Funded: 2016

Program (s): Climate Variability and Predictability Program

Competition: AMOC-Climate Linkages in NA/SA

Award Number: NA16OAR4310165, NA16OAR4310166 | View Publications on Google Scholar

Redistribution of heat, freshwater and carbon anomalies by the Atlantic Meridional Overturning Circulation (AMOC) plays an important role in regulating climate variability. The knowledge of pathways and timescales associated with AMOC is required for understanding linkages different parts of the global ocean and for interpretation of the observed variability. The progress in this direction is challenging because of the important modulations of these linkages by mesoscale eddy- induced mixing. The challenge comes in large part from the enormous computing costs of running extended numerical simulations and high spatial resolutions. Instead, vast majority of numerical studies of AMOC rely on coarse-resolution simulations, which parameterize all important small- scale processes. Despite significant advances in these parameterization schemes, their fidelity is challenging to establish, which results in biases and uncertainties in studies on the role of AMOC in climate and its variability. This is particularly important in light of the fact that the oceanic uptake of anomalous heat and anthropogenic carbon by AMOC in climate models represent one of the major sources of uncertainty in future climate projections.
The main goal of the proposed study is to examine pathways and timescales associated with AMOC and its interactions with the Southern Ocean, and to establish the relative importance of the mean advection and the material transport induced by mesoscale currents (“eddy mixing”). This goal will be achieved by using a highly efficient offline technique for tracer simulation, which allows multiple extended simulations at high spatial resolution and targeted sensitivity studies that can isolate and quantify the effects of mesoscale advection. The “boundary impulse response” will be used in high-resolution, high-fidelity numerical simulations of AMOC to obtain objective, non tracer-specific characterization of AMOC pathways and timescales. The importance of eddies and inhomogeneity of their transports will be analyzed using arguably the most accurate and straightforward technique of contrasting simulations with and without eddies, but with the same mean stratification. Finally, the results will be used for interpretation of the observed variability in the North and South Atlantic.
This proposal is in response to the “CVP - AMOC-Climate Linkages in the North and/or South Atlantic” Competition. This study is relevant to this competition because it aims to improve the understanding of linkages between various branches of AMOC and the rest of the climate system. Proposed techniques are perfectly suited for studies of the AMOC flow pathways in the presence of explicit effects of mesoscale eddies, and will help to identify important fingerprints of AMOC and to develop useful metrics for model evaluation. Progress in this direction is critical for reducing uncertainty in multi-decadal prediction of the Earth system and for interpretation of observations. The proposed work is relevant to NOAA’s long-term goal of “Climate Adaptation and Mitigation” and its objective of “Improved scientific understanding of the changing climate system and its impacts”, by offering a comprehensive, novel study of the pathways and timescales of AMOC that will lead to the improved understanding and modeling of the global ocean circulation and its effects on the Earth System, including sea level rise and changes in the biogeochemical cycles.

Understanding dramatic warming and altered fisheries on the US Continental Shelf through observations and multi-scale models

Principal Investigator(s): Jaime Palter, Kelton McMahon and Christopher Kincaid (University of Rhode Island); Paula Fratantoni and Kevin Friedland, (NOAA/NMFS/NEFSC)

Year Initially Funded: 2020

Program (s): Climate Variability & Predictability

Competition: Climate and Changing Ocean Conditions: Research and Modeling to Support the Needs of NOAA Fisheries

Award Number: NA20OAR4310483, GC20-304 | View Publications on Google Scholar

Statement of the Problem: The warming trend observed in the NEUS Continental Shelf Large Marine Ecosystem during recent decades is one of the strongest in the global ocean and has impacted regional fisheries. This warming pattern was accompanied by significant changes in the distribution, productivity, and trophic interactions of many commercially important species. Yet, the oceanographic drivers of these temperature changes have not been identified. The proposed work aims to advance our understanding of these physical processes and their connection with fisheries, ultimately leading to better predictions and preparations for future change. Methods and Summary of Work to be Completed: Our guiding hypothesis is that the increased presence of the Gulf Stream at the Tail of the Grand Banks (TGB) restricts the southwestward transport of the Labrador Current along the NEUS slope, thereby increasing the fraction of subtropical waters on the continental shelf. Because these subtropical waters substantially warm and deoxygenate the shelf, such circulation changes would strongly impact the marine ecosystem. If this hypothesis is correct, then knowing the conditions at the TGB could translate to substantial predictability for temperature-linked fisheries impacts, given that anomalies likely propagate along the slope at relatively slow advective time scales. Despite substantial preliminary evidence, a robust test of the hypothesized connection between circulation at the TGB and anomalous properties on the NEUS slope and shelf has been lacking. Thus, our proposed work will characterize the fluctuations of the Gulf Stream position relative to the TGB and the connection with shelf property and fisheries fluctuations through the following 3 objectives: 1. Reconstruct and compare historical variability in water masses, ecosystem characteristics, and fisheries at the TGB and along the NEUS slope and shelf through the coordinated analysis of satellite, hydrographic, isotopic, and fisheries data. 2. Use the observational record, alongside a numerical model, to expose the mechanisms that lead to co-variability between TGB and slope anomalies, as well as quantify the alongslope propagation time scales for these anomalies. This goal is timely given that models are only recently capable of faithfully simulating dynamics in this complex region. 3. Run a regional ocean model to explore how anomalies propagating along the slope are exchanged across the shelf. This step is necessary to understand when and how alongslope anomalies come to influence the shelf, potentially providing lead time to anticipate changes in the shelf physical environment that are crucial to ecosystems and fisheries. Relevance to the competition: The proposed work directly responds to CVP’s priority to combine observational data analysis with ocean model process studies to better quantify and understand physical changes on the NEUS continental shelf. It also evaluates the impacts of these physical changes on the distribution and migration phenology of the economically important fish and invertebrate species that are part of the Large Marine Ecosystem.

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