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Producing and diagnosing a regional analysis with data assimilation at a cloud-permitting scale to support YMC and PISTON

Principal Investigator(s): Zhaoxia Pu (University of Utah); Agie Wandala Putra (BMKG), Collaborator: Chidong Zhang (NOAA/PMEL)

Year Initially Funded: 2017

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent Region

Award Number: NA17OAR4310262 | View Publications on Google Scholar


Atmospheric convection in the Maritime Continent (MC) region undergoes substantial multi-scale variability on the diurnal, synoptic, intraseasonal, and seasonal scales. The processes governing these multiscale variabilities and interactions are essential for predicting high-impact weather and climate, especially the barrier effect of the MC on the Madden-Julian Oscillation (MJO). These processes are not well understood and are key issues motivating the planned YMC and PISTON programs. Among all the challenges, uncertainties in current global analysis products and prediction regarding temporal and spatial variability of atmospheric convection, its diurnal cycle, triggering, propagation and upscale growth, and distribution over water and land in the MC are critical factors limiting the application of such analyses to understanding these processes. The available global analysis and reanalysis products cannot accurately represent the detailed features of convective systems in the MC either temporally or spatially because of their coarse resolution (~50 km to 100 km and 6 hourly) and deficiencies in cumulus parameterization schemes. The overarching goal of this proposed project is to produce an hourly regional analysis over the MC region during the whole period of YMC at a cloud-permitting scale (~ 3 km horizontal grid spacing) using the community mesoscale Weather Research and Forecasting (WRF) model and the NCEP Gridpoint Statistical Interpolation (GSI)-based hybrid ensemble-variational data assimilation system with the assimilation of all available in-situ observations, radar data, and satellite data products during YMC, including PISTON. It is anticipated that the proposed regional analysis will reveal detailed properties of atmospheric convection and its environmental conditions that are not available from global analysis products and thus will enhance our ability to answer the following science questions: • What are the spatial and temporal distributions and variabilities of mesoscale atmospheric convective systems, their large-scale environmental conditions, and associated physical and dynamical processes during their triggering, propagation, and upscale growth, associated with the MJO? • What is the role of local-scale land-sea breezes and orography effects in convective system initiation, evolution, and propagation? How do these local-scale effects contribute to the diurnal cycle and the multiscale variability over the MC region? In addition, what are the major controlling factors that enhance their interactions with large-scale dynamic and thermodynamic conditions? What are the processes controlling the offshore diurnal migration of precipitating systems? • What are the major causes of the barrier effect of the MC on the MJO? How is the MJO affected by local-scale flows and thermodynamic conditions, such as sea-land breezes, orography effects, storm outflows, etc., in the context of the MC barrier effect? • Compared with the regional reanalysis, what are the major uncertainties and limitations of available global reanalyses in representing the physical processes of zonal propagation of the MJO and the barrier effect of the MC? • Based on the verification and validation of the quality of regional analysis in various locations, what types of observations are the most useful for better representation of the atmospheric processes and conditions critical to MJO propagation in the MC region? The proposed research directly responds to the NOAA Climate Variability and Predictability Program solicitation for proposals “that aim to improve understanding of processes that affect the propagation (speed, intensity, disruption, geographic placement) of intraseasonal oscillations in the Maritime Continent and broader region by using a combination of in situ and remote observations, data analysis, modeling, and/or theoretical understanding of local and remote processes.”

Propagation and predictability of the tropical intraseasonal oscillation in the Maritime Continent region

Principal Investigator(s): Kazuyoshi Kikuchi (University of Hawaii); George N. Kiladis (NOAA/ESRL/PSD), Kunio Yoneyama and Tomoe Nasuno (JAMSTEC), Tomoki Miyakawa (U. Tokyo)

Year Initially Funded: 2017

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent Region

Award Number: NA17OAR4310250, GC17-303 | View Publications on Google Scholar


The tropical intraseasonal oscillation (ISO) is one of the most important phenomena in the tropics. It exerts a profound influence on a wide range of weather-climate systems not only in the tropics but also in the extratropics. Thus, predicting the ISO accurately is of critical importance, although our current prediction skill of the ISO based on general circulation models (GCMs) remains unsatisfactory. This is largely due to uncertainties in model physics as well in model initialization. Of the uncertainties in model physics, the cloud and precipitation processes are particularly important. The convective component of the ISO is made up primarily of a number of mesoscale convective systems (MCSs). On the other hand, there is lots of evidence that a substantial fraction of MCSs occur in association with synoptic-scale equatorial waves, often referred to as convectively coupled equatorial waves (CCEWs). However, how the interactions among MCSs, CCEWs, and the ISO operate are poorly understood. The presence of the Maritime Continent (MC) exacerbates the situation. A pronounced diurnal cycle in conjunction with the complex geography comes into play in the interaction. As a result, the ISO convection skirts around the islands and weakens significantly, and simulating the ISO with fidelity is particularly difficult in the MC region, a strong limiting factor in our predictive skill. Taking advantage of the YMC opportunity, this project aims to improve our understanding of the processes that affect the propagation of the ISO in the MC region, especially from the viewpoint of multiscale interaction, through synergistic use of both observations and state-of-the-art numerical models. Because of the diversity in the ISO, a thorough and comprehensive observational and modeling treatment will be the key to any successful diagnosis of ISO dynamics and physics. In this research, we will carefully identify the types of ISOs based on three different indices. We hypothesize from our previous results that CCEWs play a central role in the propagation of the ISO. Novel objective methods including the spatio-temporal wavelet transform (STWT) and objective-based tracking approach will be used to test our hypothesis from morphological point of view. Rigorous analysis of moisture, momentum, and temperature fields with respect to CCEWs, MCSs, and other prominent synoptic-scale components will help us quantify the roles of individual components in the propagation of the ISO. We will further use forecasts of conventional GCMs including CFSv2 and a global-cloud resolving model, NICAM, to examine the processes that are responsible for the propagation of the ISO. By conducting a meticulous comparison among observations, conventional GCMs’ forecasts, and NICAM forecasts in terms of both morphology and budget approaches, it is anticipated that we will gain invaluable insights into the convective processes that affect the propagation and thus predictability of the ISO. Although we will pay special attention to YMC, we will make use of past field campaign opportunities including the CINDY/DYNAMO (October 2011-March 2012) and Pre-YMC (November-December 2015) as well as long-term observational and forecast data in an attempt to draw statistically robust conclusions. Our research will contribute not only to advancing our understanding of the propagation and structure of the ISO, but also to identifying the problematic processes in models simulating the ISO in the MC, which eventually contribute to improving their predictability of the ISO. The objective of this project is entirely in line with the CVP’s goal that “aims to improve understanding of processes that affect the propagation (speed, intensity, disruption, geographic placement) of intraseasonal oscillations in the Maritime Continent and broader region by using a combination of in situ and remote observations, data analysis, modeling and/or theoretical understanding of local and remote processes” as well as NOAA’s long-term climate goals.

Role of Air-Sea-Land Interaction in the MJO Prediction Barrier over the Maritime Continent: A Cloud-Resolving Coupled Modeling Study

Principal Investigator(s): Shuyi Chen (University of Washington), Chris Fairall (NOAA/ESRL)

Year Initially Funded: 2017

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent Region

Award Number: GC17-308 | View Publications on Google Scholar


The global impact of the MJO depends on whether its convection center is located over the Indian Ocean, Maritime Continent (MC), or western Pacific. In observations, not all MJO events initiated over the Indian Ocean propagate through the MC. This is known as the MJO barrier over the MC. This barrier effect is exaggerated in numerical prediction models, creating an MJO prediction barrier problem with particularly low prediction skill for the MJO moving through the MC. This MJO prediction barrier problem inevitably hinders our ability of accurately predicting global weather, including high-impact events, on subseasonal timescales. Reasons behind the MJO barrier effect of the MC, in models as well as in nature, are subjects of debate. The MJO prediction barrier problem of the MC must be resolved to advance subseasonal prediction. In this proposed research, we plan to investigate the MJO prediction barrier problem. We will treat air-sea-land interaction within the MC region as a centerpiece linking other processes that possibly are crucial to the MJO barrier problem. These processes include the diurnal cycle, land, topography, and atmospheric convection. An important aspect of air-sea-land interaction in the MC is its close connection with the unique land-sea geography, where the local land-sea circulation on the diurnal timescale interacts with the MJO. The focus on air-sea-land interaction is motivated by observational and modeling results that main convection signals of the MJO in the MC are over water, and SST and convection of the MC are sensitive to upper-ocean mixing within the MC. We hypothesize that the MJO barrier effect of the MC is exaggerated in models because air-sea-land interaction processes are not adequately represented, even by coupled models of coarse resolutions. We propose to test this hypothesis through modeling experiment using a cloud-resolving coupled atmosphere-ocean model that has demonstrated its capability of reproducing the MJO propagation through the MC. The general strategy of this study is to first select MJO events that propagated through the MC in observations but failed in global model forecasts. For a given MJO event, a set of model simulations will be made, with a specific model configuration for each simulation (with or without land, air-sea coupling, tidal mixing, and the diurnal cycle; high- or low-resolution representation of topography; parameterized or explicit atmospheric convection). Through diagnosing these simulations, we will isolate and quantify effects on simulated MJO propagation through the MC by air-sea-land interaction, the diurnal cycle, topography, and treatment of convection. Observations from ONR PISTON and international YMC field campaigns will be used to evaluate coupled model results when they become available during this proposed study. This proposed research is in response to the CVP solicitation − Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent Region, which “aim to improve understanding of processes that affect the propagation (speed, intensity, disruption, geographic placement) of intraseasonal oscillations in the Maritime Continent and broader region by using a combination of in situ and remote observations, data analysis, modeling, and/or theoretical understanding of local and remote processes”. Results from this project would provide a better understanding and quantitative assessment on possible sources of the MJO prediction barrier problem in numerical models. This would guide the strategy of model development and improvement of MJO prediction in general, and help fulfill NOAA’s long-term climate goal of improved scientific understanding of the changing climate system and its impacts, and address challenges in weather and climate extremes.

Ship-based Observations of Atmospheric Boundary and Ocean Interactions near the Philippines during PISTON

Principal Investigator(s): Chris Fairall (NOAA/ESRL/PSD), Alan Brewer (NOAA/ESRL/CSD)

Year Initially Funded: 2017

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent Region

Award Number: GC17-301 | View Publications on Google Scholar


The Madison-Julian Oscillation (MJO) is a major source of variability and predictability in the equatorial ocean. The Indian Ocean is usually referred to as the birthplace of the MJO. As the MJO propagates to the East it encounters the Maritime Continent (MC) where it may die out, propagate into the Pacific Ocean, and/or trigger the Boreal Summer Intraseasonal Oscillation (BSISO). The BSISO propagates from the equatorial Maritime Continent northward over the Philippine Archipelago. Intraseasonal atmospheric variability offers the possibility of better 10-day predictions, yet its predictability remains elusive. Furthermore, the local response of the atmosphere-oceanland system to intraseasonal and synoptic atmospheric variability is not understood. The local response involves terrain blocking the flow, diurnal land sea breezes that locally enhance and/or interrupt synoptic-scale waves, and different surface feedbacks between the mostly vegetated land surface and the ocean mixed layer. The MJO-barrier is poorly captured in climate models; the reason is hypothesized to be associated with conflicting land vs oceanic convective diurnal cycles. To address this, NOAA and partners (ONR, NASA, DOE) are planning a major field and modeling study in the MC called Propagation of IntraSeasonal Tropical Oscillations (PISTON). We propose to make observations of ocean surface conditions, including fluxes of heat, moisture, and momentum, and the atmospheric boundary layer as part of PISTON in summer 2018 aboard a research vessel within the waters and the vicinity of the Philippine Archipelago. The research vessel permits us to sample different atmosphere-ocean interactions to incoming rain and wind events as a function of such parameters as distance offshore (0-300 km from shore), water depth, and island blocking of prevailing and anomalous wind. We expect nearshore diurnal circulations associated with the islands to superpose and interact with synoptic storm conditions propagating into the island regions. We will measure the ocean wave state, sea surface temperature, and turbulent fluxes of sensible and latent heat and momentum across the atmosphere-ocean interface. A unique array of in situ and remote sensing instruments continuously measures turbulence and its effects on the momentum, heat, water, and salinity budgets. Together the observing systems proposed for the ship vertically profile temperature, moisture, and turbulent velocities from the ocean mixed layer, through the air-sea interface, atmospheric surface and planetary boundary layer, to shallow clouds. Our measurements will be a major contributor to high resolution modelling performed by research partners at Oregon State University (already funded for PISTON).

Spatial structure of diurnal variability from profiling float arrays

Principal Investigator(s): T. M. Shaun Johnston (Scripps); Daniel L. Rudnick (Scripps)

Year Initially Funded: 2017

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent Region

Award Number: NA17OAR4310259 | View Publications on Google Scholar


Relevance. This proposal is submitted to the Climate Variability and Predictability Program (CVP)-Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent (MC) Region. This project addresses NOAA’s and CVP’s goals by observing the upper ocean at high temporal and vertical resolution during the active and suppressed phases of a Madden-Julian Oscillation (MJO). This coupled-air sea phenomenon affects El Nino, monsoons, cyclones, and atmospheric rivers either directly or through atmospheric teleconnections. Global climate models have difficulty accurately predicting the propagation of MJO through the varied topography and enclosed seas of the MC. Better MJO prediction requires high spatial and temporal resolution of the diurnal cycle in observations and models because of diurnal effects on sea surface temperature (SST). Amidst a varying background (mesoscale, MJO phase, and lateral gradients in diurnal and mean structure of winds, precipitation, and stratification), arrays of state-of-the-art autonomous profiling floats will observe subsurface processes affecting (a) diurnal SST variability and (b) thin salinity-controlled upper ocean mixed layers, which in turn produce enhanced SST variability. Diurnal cycle. The Years of the Maritime Continent (YMC) Science Plan notes, that models poorly predict the observed diurnal variability in the MC and the barrier effect of the MC on MJO. Diurnal SST both modulates and is modulated by MJO: diurnal SST affects the initiation, propagation, and strength of MJO, while MJO affects diurnal insolation and heat fluxes. The diurnal cycle of mixing raises and lowers the mixed layer depth. The diurnal wind’s propagation across the MC’s enclosed seas is affected by SST and geography of islands and seas. Therefore, spatially and temporally extensive measurements of the diurnal cycle in the upper ocean are needed. Subsurface processes affecting SST. Fresh water input from June–October into the South China Sea (SCS), for example, produces a mixed layer controlled by salinity (S) and a roughly isothermal layer beneath, which isolates the mixed layer from cooler thermocline waters. Heat fluxes are concentrated into a thin mixed layer and enhance SST variability. Therefore, accurate SST prediction requires high vertical and temporal resolution observations and modeling of processes affecting not only SST, but also subsurface S and stratification. The spatial S structure depends on lateral stirring and vertical mixing of fresher surface waters. Spatially extensive measurements of S variability at different sites and times are needed to forecast SST. Plan. These measurements will augment intensive observations in the SCS by PISTON and around the southern MC by Australia’s YMC program in 2018. Floats will be seeded in the SCS and around the MC, in a region of varying S, diurnal amplitude, and winds. Eight floats will be deployed but not recovered from each of R/V Thompson in PISTON and R/V Investigator in YMC in a nominal 50 km box with the flow dispersing the floats over a larger area. The SOLO-II float is a proven tool in the ARGO program and will be optimized here for rapid, shallow profiling. Arrays of SOLO-II floats will yield extensive 3-D coverage of the upper ocean over 30 days via clean, near-surface, high-vertical resolution profiles of T and S from 0–50 m every 25 minutes and produce ∼3500 profiles/float. Alternatively 250-m profiles provide 90-day endurance and ∼1600 profiles/float. Float arrays provide spatial coverage as does the drift of each float. In total, up to 57,000 T and S profiles to 50 m will be obtained (or 26,000 profiles to 250 m).

The Role of Ocean Stratification in the Propagation of Intraseasonal Oscillations

Principal Investigator(s): Janet Sprintall (Scripps)

Year Initially Funded: 2017

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent Region

Award Number: NA17OAR4310257 | View Publications on Google Scholar


Intraseasonal Madden-Julian Oscillation (MJO) atmospheric forcing exerts a profound influence on the near ocean surface layer of the tropics through the coupled air-sea system that in turn affects the structure, development and propagation of the mesoscale convective systems that are part of the MJO. Models suggest that an accurate depiction of the upper ocean stratification in the MC is necessary to correctly reproduce intraseasonal variability. Nonetheless, the dynamics and time scales of the processes and characteristics at the air-sea interface during MJO events are still not well understood. One large gap in our understanding is the role of upper ocean salinity in MJO variability. Since salinity controls stratification throughout much of the MC it can play a critical role in the complex coupling of the air-sea system during MJO events. In many MC regions, a salt-stratified but isothermal “barrier layer” can exist that traps fluxes of heat, freshwater, and momentum to a thin surface layer. Climatological variations in the thickness of the barrier layer during MJO events are known to drive SST anomalies that influence the coupled air-sea system. Similarly, few studies of the diurnal-intraseasonal interaction within the MC have considered the role played by salinity in setting the diurnal ocean stratification. Yet the global maximum in sea surface salinity diurnal amplitude lies within the MC region. The main aim of the proposed effort is to understand the mechanisms responsible for upper ocean stratification variability in the MC, with a particular attention on near surface salinity stratification and how this influences the structure and propagation of MJO convection and winds. High-resolution ship-board measurements of the upper ocean temperature and salinity will be obtained using a portable underway CTD (uCTD) system. The data will provide distinct case studies of the ocean conditions during MJO events, that will be examined in concert with remotely-sensed and other in situ datasets, with science objectives to (1) determine the characteristics and the time and space scales of upper ocean salinity variability of importance to MJO variability; (2) identify the main forcing mechanisms that control that salinity variability; and (3) establish connection with the intraseasonal MJO atmospheric phenomena and relationship to the propagation characteristics (speed, intensity, MJO phase, geographical location etc) of the MJO across the MC region. Relevance to Competition: The proposed research is a contribution to the CVP - Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent Region. The MJO is the dominant mode of intraseasonal variability in the global tropics influencing the monsoon systems, convective patterns, cyclogenesis and triggering of El Niño events. The MC plays a special role in the behavior of the MJO, critically affecting the propagation speed and intensity of the convective systems in ways that are not yet fully understood. The proposed research aims to provide new information on the processes that control upper ocean stratification in the MC region and so enable a better representation and prediction in models of the characteristics, structure and evolution of the MJO propagation in the MC. The project directly addresses the key NOAA long-term goal of improving scientific understanding of the Earth’s climate variability.

Upper ocean processes in the Maritime Continent and their impact on the air-sea interaction and MJO predictability

Principal Investigator(s): Toshiaki Shinoda (Texas A&M University - Corpus Christi); Hyodae Seo (WHOI), Wanqiu Wang (NOAA/NCEP/CPC)

Year Initially Funded: 2017

Program (s): Climate Variability & Predictability

Competition: Observing and Understanding Processes Affecting the Propagation of Intraseasonal Oscillations in the Maritime Continent Region

Award Number: NA17OAR4310256, NA17OAR4310255, GC17-306 | View Publications on Google Scholar


“Years of Maritime Continent (YMC)” is an international campaign, which contains five scientific themes. The project we propose will focus primarily on upper ocean processes and their impacts on air-sea interaction, and thus will directly contribute to one of the themes “Ocean and Air-Sea Interaction”. The primary goal of the proposed study is to understand the role of upper ocean processes over the Maritime Continent (MC) in diurnal to intraseasonal atmosphereocean land interaction and the simulation and prediction of the tropical intra-seasonal variability including the MJO. Specific objectives are to: • Determine the large-scale impact of the diurnal air-sea-land interaction on the simulation and prediction skill of the MJO propagation across the MC. • Examine the impact of oceanic processes on diurnal and intraseasonal rainfall evolution and propagation over the Indonesian seas. To achieve the goal described above, we will combine three different coupled models: NCEP CFS, the global NAVGEM/HYCOM system, and the regional WRF/ROMS model. A series of model simulations will be first conducted using NCEP CFS and the NAVGEM/HYCOM system to identify the impact of diurnal variation on MJO propagation through the MC. To assess the relative impact of the diurnal cycle over the land and the ocean on the regional intraseasonal rainfall and the MJO simulations, predictability experiments will be carried out by selectively switching off the diurnal variations in land surface temperature and SST only in the MC domain. Model skills of prediction in each simulation will be examined to isolate the impact of diurnal variability on the prediction skill. The results will be compared with high-resolution regional WRF/ROMS simulations. The WRF/ROMS system will downscale the CFS and NAVGEM/HYCOM simulations in a multi-nesting tropical channel configuration, with enhanced resolution in the MC domain up to an explicit convection scale (3-4 km). To examine the effect of upper ocean processes on air-sea interaction and the MJO, we will conduct a series of sensitivity experiments. Various methods, which were used in previous studies, will be applied for WRF/ROMS experiments. From the experiments with two-way interaction between the nested MC domain with explicit convection and the parent tropical channel domain at a coarser resolution (40 km), we will assess the upscaling impact of the MC regional processes on the MJO. The combined global and regional coupled model simulations will identify “hot spots” within the MC with the strongest air-sealand coupling, where the MJO simulation and forecast skill are most sensitive to.

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.

The Western Transition Zone as a Gatekeeper for the North Atlantic MOC Throughput

Principal Investigator(s): Martha Buckley (George Mason University), Susan Lozier (Duke University)

Year Initially Funded: 2016

Program (s): Climate Variability and Predictability

Competition: AMOC-Climate Linkages in NA/SA

Award Number: NA16OAR4310167, NA16OAR4310168 | View Publications on Google Scholar


The Atlantic Meridional Overturning Circulation (AMOC) requires significant transport between  the North Atlantic subtropical and subpolar gyres. This transport contributes appreciably to the  Atlantic’s mean ocean heat transport and its variability has been linked to climate variations on  a wide range of time scales, including paleoclimate shifts and Atlantic multidecadal sea surface  temperature variability. Despite the importance to our climate system, no clear consensus on the  dynamical mechanisms controlling this throughput and its variability has emerged to date. Fur- thermore, recent Lagrangian studies have challenged the traditional understanding of the geometry  of the throughput in both the upper and lower AMOC limbs. The goal of our work is to build on  past Eulerian and Lagrangian studies in order to work toward a consensus on AMOC variability  mechanisms.
We believe that such a consensus is possible with a focus on the dynamics at the western margin of  the subtropical-subpolar gyre boundary, a region referred to as the western transition zone (WTZ).  Our working hypothesis is that the WTZ is a gatekeeper for the throughput, whereby buoyancy  anomalies in the WTZ establish the throughput variability and influence decadal AMOC variability  in both the subtropical and subpolar gyres. Importantly, buoyancy anomalies in the WTZ are not  forced solely by local processes; rather they are the result of a wide array of ocean processes.  Thus, we may consider the WTZ an integrator of various processes, a view that may reconcile  various proposed mechanisms of AMOC variability, such as the influences of deep convection and  Rossby waves. As such, a focus on the WTZ may considerably aid the interpretation of AMOC  measurements across the RAPID and OSNAP lines.
Using Eulerian and Lagrangian studies, conducted with ocean observations and two ocean mod- els, our proposed work will address the following questions: (1) Do temporal changes in WTZ  buoyancy anomalies align with throughput changes measured in the Lagrangian frame? (2) What  mechanism creates these buoyancy anomalies? (3) On interannual to decadal time scales, what is  the relationship between WTZ buoyancy anomalies and AMOC variability in the subtropical and  subpolar gyres? To answer these questions we will: quantify AMOC pathways through the WTZ  and develop a Lagrangian metric of the throughput; use Lagrangian experiments and statistical  analyses to investigate the relationship between throughput variability and WTZ buoyancy anoma- lies; use buoyancy budgets, ocean model experiments, and adjoint experiments to understand the  origin of buoyancy anomalies in the WTZ; and determine the extent to which WTZ buoyancy and  AMOC anomalies are related to buoyancy and AMOC anomalies at other latitudes.
Our proposal is targeted at the competition “AMOC-Climate Linkages in the North/South At- lantic”, and is directly relevant to its program objectives, as well as to these research priorities  highlighted in the US AMOC 2014 annual report: (1) Provide a more detailed understanding of  AMOC flow pathways and their impact on variability; (2) Investigate connections between surface  forcing and AMOC variability; (3) Continue investigation of AMOC “fingerprints”; (4) Synthe- size results from theoretical, idealized models, and complex GCM investigations into a common  conceptual framework regarding key AMOC variability mechanisms. More broadly, our proposal  advances the field of decadal prediction by developing an improved understanding of the dynamics  of important modes of climate variability, such as the AMOC, which must be accurately captured  in models used to make decadal predictions.

Understanding the freshwater budget of the Atlantic Ocean: Controls, Responses, and the Role of the AMOC

Principal Investigator(s): Wei Cheng (University of Washington), John Chiang (UC Berkeley), Gokhan Danabasoglu (National Center for Atmospheric Research), Wilbert Weijer (Los Alamos National Laboratory), Dongxiao Zhang (University of Washington)

Year Initially Funded: 2016

Program (s): Climate Variability and Predictability

Competition: AMOC-Climate Linkages in NA/SA

Award Number: NA16OAR4310169, NA16OAR4310170, NA16OAR4310171 | View Publications on Google Scholar


The Atlantic Meridional Overturning Circulation (AMOC) is an interactive player in the Atlantic  Ocean freshwater budget. In model simulations, the AMOC responds to surface freshwater flux  (precipitation – evaporation + river runoff + ice melt; “P-E+R+M”) perturbations in the subpolar  North Atlantic; it is also influenced by P-E+R+M over the broader Atlantic through salt/freshwater  advection and inter-basin exchanges (e.g., Agulhas Leakage). In turn, the AMOC drives changes in  salt transport across 35oS and affects P-E+R+M through its influence on Atlantic sea surface  temperature, sea ice extent, and other processes. Yet, the intrinsic time scales and mechanisms driving and responding to Atlantic Ocean freshwater budget variability are not known. Moreover, changes in the global hydrological cycle, melting of the Greenland Ice Sheet, and retreat of Arctic  sea ice are among the most robust features of climate projections. We propose to investigate the  interconnections between P-E+R+M and oceanic transport of heat and freshwater/salt; and how  they affect, and are influenced by, AMOC variability on decadal to multidecadal timescales. We will perform targeted analyses of representative Coupled Model Inter-comparison Project Phase 5  (CMIP5) models; the new AMOC ensemble of NSF-DOE CESM; an eddy-permitting simulation  with the Accelerated Climate Modeling for Energy (ACME) v0 model; and output from ACME v1,  when it becomes available. In addition, we will perform perturbation experiments using the standard-resolution CESM. The objectives are: 
1. Investigate the spatio-temporal patterns of P-E+R+M associated with the AMOC  variability in the selected coupled simulations; examine how they project onto the total surface  freshwater flux variability, and how they differ among the models; 
2. Analyze the freshwater budget of the Atlantic Ocean in selected coupled climate  simulations, focusing on the interplay between P-E+R+M, storage, and interocean exchanges  due to the AMOC, the wind-driven circulation, and interocean exchange; identify drivers and  response terms, the time scales on which they operate, and their controls; 
3. Investigate the role of Agulhas Leakage in the freshwater budget of the Atlantic, by tracing  the pathway of Agulhas Leakage water through the Atlantic, and assessing its impact on the  Atlantic stratification and the AMOC; 
4. Elucidate the physical mechanisms and feedbacks that connect P-E+R+M forcing, oceanic  freshwater transport adjustment and AMOC variability through targeted experimentation using  the CESM. 
This research is responding to “CVP - AMOC-Climate Linkages in the North and/or  South Atlantic” competition. The proposed model evaluation will utilize existing and emerging  observations; the sensitivity experiments and tracer simulations are designed to understand flow  pathways of the AMOC, and how they respond to surface and inter-basin forcing changes. Both of  these aspects are listed priorities of the CVP solicitation. We anticipate that our results will improve  comparison between climate model simulations and measurements. This research also addresses an  objective of NOAA’s long-term climate goals outlined in NOAA’s Next-Generation Strategic Plan,  namely, improved scientific understanding of the changing climate system and its impacts.



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