Joyce Terrence M.

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Terrence M.

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  • Article
    Influence of the Kuroshio interannual variability on the summertime precipitation over the East China Sea and adjacent area
    (American Meteorological Society, 2019-04-01) Gan, Bolan ; Kwon, Young-Oh ; Joyce, Terrence M. ; Chen, Ke ; Wu, Lixin
    Much attention has been paid to the climatic impacts of changes in the Kuroshio Extension, instead of the Kuroshio in the East China Sea (ECS). This study, however, reveals the prominent influences of the lateral shift of the Kuroshio at interannual time scale in late spring [April–June (AMJ)] on the sea surface temperature (SST) and precipitation in summer around the ECS, based on high-resolution satellite observations and ERA-Interim. A persistent offshore displacement of the Kuroshio during AMJ can result in cold SST anomalies in the northern ECS and the Japan/East Sea until late summer, which correspondingly causes anomalous cooling of the lower troposphere. Consequently, the anomalous cold SST in the northern ECS acts as a key driver to robustly enhance the precipitation from the Yangtze River delta to Kyushu in early summer (May–August) and over the central ECS in late summer (July–September). In view of the moisture budget analysis, two different physical processes modulated by the lateral shift of the Kuroshio are identified to account for the distinct responses of precipitation in early and late summer, respectively. First, the anomalous cold SST in the northern ECS induced by the Kuroshio offshore shift is likely conducive to the earlier arrival of the mei-yu–baiu front at 30°–32°N and its subsequent slower northward movement, which may prolong the local rainy season, leading to the increased rain belt in early summer. Second, the persistent cold SST anomalies in late summer strengthen the near-surface baroclinicity and the associated strong atmospheric fronts embedded in the extratropical cyclones over the central ECS, which in turn enhances the local rainfall.
  • Technical Report
    Warm core ring cruise #1 : R/V Endeavor cruise no. 74
    (Woods Hole Oceanographic Institution, 1982-07) Stalcup, Marvel C. ; Joyce, Terrence M. ; Schmitt, Raymond W. ; Dunworth, Jane A.
    At 1300 hours on 12 September 1981 the research vessel ENDEAVOR departed Woods Hole on a 22 day cruise to study the physical, chemical and biological structure of warm core ring 81-D. The cruise was the first of 5 ENDEAVOR cruises planned as part of the NSF/NASA-sponsored Warm Core Ring study.
  • Technical Report
    Acoustic doppler current profiling in the Western Pacific during the WOCE P10 cruise, November/December 1993
    (Woods Hole Oceanographic Institution, 1997-04) Bahr, Frank B. ; Joyce, Terrence M.
    The objective of this cruise was to occupy a hydrographic section nominally along 149E from Papua New Guinea to the shelf off the coast of Japan near Yokohama as part of the one-time WOCE Hydrographic Programe survey of the Pacific Ocean, line P10. This report describes the processing of shipboard acoustic Doppler current profier (ADCP) data that were collected during this cruise. New GPS-based heading measurements ("Ashtech heading"). which increase the accuracy of the ADCP, are covered in detail. A subset of the processed data from the New Guinea Coastal Undercurrent and from the Kuroshio is presented.
  • Preprint
    Enhanced warming over the global subtropical western boundary currents
    ( 2011-11) Wu, Lixin ; Cai, Wenju ; Zhang, Liping ; Nakamura, Hisashi ; Timmermann, Axel ; Joyce, Terrence M. ; McPhaden, Michael J. ; Alexander, Michael A. ; Qiu, Bo ; Visbeck, Martin ; Chang, Ping ; Giese, Benjamin
    Subtropical western boundary currents are warm, fast flowing currents that form on the western side of ocean basins. They carry warm tropical water to the mid-latitudes and vent large amounts of heat and moisture to the atmosphere along their paths, affecting atmospheric jet streams and mid-latitude storms, as well as ocean carbon uptake. The possibility that these highly energetic and nonlinear currents might change under greenhouse gas forcing has raised significant concerns, but detecting such changes is challenging owing to limited observations. Here, using reconstructed sea surface temperature datasets and newly developed century-long ocean and atmosphere reanalysis products, we find that the post-1900 surface ocean warming rate over the path of these currents is two to three times faster than the global mean surface ocean warming rate. The accelerated warming is associated with a synchronous poleward shift and/or intensification of global subtropical western boundary currents in conjunction with a systematic change in winds over both hemispheres. This enhanced warming may reduce ocean's ability to absorb anthropogenic carbon dioxide over these regions. However, uncertainties in detection and attribution of these warming trends remain, pointing to a need for a long-term monitoring network of the global western boundary currents and their extensions.
  • Article
    Impact of multidecadal variability in Atlantic SST on winter atmospheric blocking
    (American Meteorological Society, 2019-12-31) Kwon, Young-Oh ; Seo, Hyodae ; Ummenhofer, Caroline C. ; Joyce, Terrence M.
    Recent studies have suggested that coherent multidecadal variability exists between North Atlantic atmospheric blocking frequency and the Atlantic multidecadal variability (AMV). However, the role of AMV in modulating blocking variability on multidecadal times scales is not fully understood. This study examines this issue primarily using the NOAA Twentieth Century Reanalysis for 1901–2010. The second mode of the empirical orthogonal function for winter (December–March) atmospheric blocking variability in the North Atlantic exhibits oppositely signed anomalies of blocking frequency over Greenland and the Azores. Furthermore, its principal component time series shows a dominant multidecadal variability lagging AMV by several years. Composite analyses show that this lag is due to the slow evolution of the AMV sea surface temperature (SST) anomalies, which is likely driven by the ocean circulation. Following the warm phase of AMV, the warm SST anomalies emerge in the western subpolar gyre over 3–7 years. The ocean–atmosphere interaction over these 3–7-yr periods is characterized by the damping of the warm SST anomalies by the surface heat flux anomalies, which in turn reduce the overall meridional gradient of the air temperature and thus weaken the meridional transient eddy heat flux in the lower troposphere. The anomalous transient eddy forcing then shifts the eddy-driven jet equatorward, resulting in enhanced Rossby wave breaking and blocking on the northern flank of the jet over Greenland. The opposite is true with the AMV cold phases but with much shorter lags, as the evolution of SST anomalies differs in the warm and cold phases.
  • Article
    Moored observations of the Deep Western Boundary Current in the NW Atlantic: 2004–2014
    (John Wiley & Sons, 2017-09-15) Toole, John M. ; Andres, Magdalena ; Le Bras, Isabela A. ; Joyce, Terrence M. ; McCartney, Michael S.
    A moored array spanning the continental slope southeast of Cape Cod sampled the equatorward-flowing Deep Western Boundary Current (DWBC) for a 10 year period: May 2004 to May 2014. Daily profiles of subinertial velocity, temperature, salinity, and neutral density are constructed for each mooring site and cross-line DWBC transport time series are derived for specified water mass layers. Time-averaged transports based on daily estimates of the flow and density fields in Stream coordinates are contrasted with those derived from the Eulerian-mean flow field, modes of DWBC transport variability are investigated through compositing, and comparisons are made to transport estimates for other latitudes. Integrating the daily velocity estimates over the neutral density range of 27.8–28.125 kg/m3 (encompassing Labrador Sea and Overflow Water layers), a mean equatorward DWBC transport of 22.8 × 106 ± 1.9 × 106 m3/s is obtained. Notably, a statistically significant trend of decreasing equatorward transport is observed in several of the DWBC components as well as the current as a whole. The largest linear change (a 4% decrease per year) is seen in the layer of Labrador Sea Water that was renewed by deep convection in the early 1990s whose transport fell from 9.0 × 106 m3/s at the beginning of the field program to 5.8 × 106 m3/s at its end. The corresponding linear fit to the combined Labrador Sea and Overflow Water DWBC transport decreases from 26.4 × 106 to 19.1 × 106 m3/s. In contrast, no long-term trend is observed in upper ocean Slope Water transport. These trends are discussed in the context of decadal observations of the North Atlantic circulation, and subpolar air-sea interaction/water mass transformation.
  • Working Paper
  • Technical Report
    Description and evaluation of the Acoustic Profiling of Ocean Currents (APOC) System used on R.V. Oceanus cruise 96 on May 11-22, 1981
    (Woods Hole Oceanographic Institution, 1982-11) Joyce, Terrence M. ; Rintoul, Stephen R. ; Barbour, R. Lorraine
    The underway current profiling system used in this study consists of a microprocessor-controlled data logger that collects and formats data from a four-beam Ametek-Straza 300 kHz acoustic Doppler current profiler, heading from the ship's gyrocompass, and navigation information from a Loran-C receiver and a satellite navigation unit. Data are recorded on magnetic tape and some real time calculations are made. The system was first used on a May, 1981 cruise aboard the R.V. OCEANUS in the western North Atlantic. Horizontal currents were profiled to depths of 100m. Time averaging is required to remove effects of ship motion. Errors in our ability to profile ocean currents are estimated to be 5-10 em s-1 for a ten-minute vector average. An intercomparison is made with a moored vector measuring current meter (VMCM). The mean difference in hourly-averaged APOC and VMCM currents over the four-hour intercomparison is a few mm s-1. Data from a variety of oceanic regimes are presented and discussed: these regimes include two Gulf Stream crossings, a warm core ring survey, and shallow water in a frontal zone to the east of Nantucket Shoals.
  • Article
    Long-term SST variability on the Northwest Atlantic continental shelf and slope
    (American Geophysical Union, 2020-01-06) Chen, Zhuomin ; Kwon, Young-Oh ; Chen, Ke ; Fratantoni, Paula S. ; Gawarkiewicz, Glen G. ; Joyce, Terrence M.
    The meridional coherence, connectivity, and regional inhomogeneity in long‐term sea surface temperature (SST) variability over the Northwest Atlantic continental shelf and slope from 1982–2018 are investigated using observational data sets. A meridionally concurrent large SST warming trend is identified as the dominant signal over the length of the continental shelf and slope between Cape Hatteras in North Carolina and Cape Chidley, Newfoundland and Labrador, Canada. The linear trends are 0.37 ± 0.06 and 0.39 ± 0.06 °C/decade for the shelf and slope regions, respectively. These meridionally averaged SST time series over the shelf and slope are consistent with each other and across multiple longer observational data sets with records dating back to 1900. The coherence between the long‐term meridionally averaged time series over the shelf and slope and basin‐wide averaged SST in the North Atlantic implies approximately two thirds of the warming trend during 1982–2018 may be attributed to natural climate variability and the rest to externally forced change including anthropogenic warming.
  • Preprint
    Using Argo data to investigate the Meridional Overturning Circulation in the North Atlantic
    ( 2009-08-06) Hernandez-Guerra, Alonso ; Joyce, Terrence M. ; Fraile-Nuez, Eugenio ; Velez-Belchi, Pedro
    Using a variety of oceanographic data, including direct volume transports in the Florida 19 Strait, and Argo float profiles and drift velocities at 24 and 36N in the North Atlantic, inverse calculations are presented in which the net meridional transport, 20 down to a depth of approximately 1600 m, is estimated at both latitudes for a five year period 2003-2007. The upper ocean is divided into 7 layers using neutral density, and mass conservation constraints have been applied to a closed box bounded by these latitudes, including the Florida Strait. Ekman layer transports have been included in the top-most layer, and the inverse calculation has solved for changes from the initial reference velocities, Ekman and Florida Strait transports, given a priori estimates on the accuracy of each of these quantities. Solutions with and without transformations due to Mediterranean Water (MW) formation are made. Our results indicate that 1) time-averaged transport estimates derived from Argo have significant less eddy noise than individual hydrographic sections, 2) Argo drift velocities provide information to the inverse solution for the ocean interior, and 3) comparison of the total integrated interior mass transports in the thermocline waters for the period 2003-2007 with the previous estimates based on trans-ocean hydrographic sections shows that the Meridional Overturning Circulation has not significantly changed since 1957.
  • Technical Report
    Hydrographic data from warm core ring 82-B
    (Woods Hole Oceanographic Institution, 1985-07) Stalcup, Marvel C. ; Joyce, Terrence M. ; Barbour, R. Lorraine ; Dunworth, Jane A.
    Hydrographic data are presented from three cruises to Warm Core Ring 82-B during April-August 1982. These data include a sampling of the 2 db pressure, temperature, salinity and oxygen measurements obtained with a CTD-02 profiler, manufactured by Neil Brown Instrument Systems, together with water sample measurements of salinity, oxygen, silica, nitrate and phosphate. Charts showing the station positions and selected profiles of the various parameters are presented. Bi-monthly cruises aboard the R/V Endeavor show only slight changes in the ring between April and June. Interactions between the ring and the Gulf Stream before the August cruise however, reduced the volume of the central core of the ring by about 90 percent.
  • Article
    Gulf Stream variability in the context of quasi‐decadal and multidecadal Atlantic climate variability
    (John Wiley & Sons, 2018-10-20) McCarthy, Gerard D. ; Joyce, Terrence M. ; Josey, Simon A.
    The Gulf Stream plays an important role in North Atlantic climate variability on a range of timescales. The North Atlantic is notable for large decadal variability in sea surface temperatures (SST). Whether this variability is driven by atmospheric or oceanic influences is a disputed point. Long time series of atmospheric and ocean variables, in particular long time series of Gulf Stream position, reveal differing sources of SST variability on quasi‐decadal and multidecadal timescales. On quasi‐decadal timescales, an oscillatory signal identified in the North Atlantic Oscillation (NAO) controls SST evolution directly via air‐sea heat fluxes. However, on multidecadal timescales, this relationship between the NAO and SST changes, while the relationship between the NAO and Gulf Stream position remains consistent in phase and resonant in amplitude. Recent changes in the Gulf Stream Extension show a weakening and broadening of the current, consistent with increased instability. We consider these changes in the context of a weakening Atlantic overturning circulation.
  • Article
    On the relationship between synoptic wintertime atmospheric variability and path shifts in the Gulf Stream and the Kuroshio Extension
    (American Meteorological Society, 2009-06-15) Joyce, Terrence M. ; Kwon, Young-Oh ; Yu, Lisan
    Coherent, large-scale shifts in the paths of the Gulf Stream (GS) and the Kuroshio Extension (KE) occur on interannual to decadal time scales. Attention has usually been drawn to causes for these shifts in the overlying atmosphere, with some built-in delay of up to a few years resulting from propagation of wind-forced variability within the ocean. However, these shifts in the latitudes of separated western boundary currents can cause substantial changes in SST, which may influence the synoptic atmospheric variability with little or no time delay. Various measures of wintertime atmospheric variability in the synoptic band (2–8 days) are examined using a relatively new dataset for air–sea exchange [Objectively Analyzed Air–Sea Fluxes (OAFlux)] and subsurface temperature indices of the Gulf Stream and Kuroshio path that are insulated from direct air–sea exchange, and therefore are preferable to SST. Significant changes are found in the atmospheric variability following changes in the paths of these currents, sometimes in a local fashion such as meridional shifts in measures of local storm tracks, and sometimes in nonlocal, broad regions coincident with and downstream of the oceanic forcing. Differences between the North Pacific (KE) and North Atlantic (GS) may be partly related to the more zonal orientation of the KE and the stronger SST signals of the GS, but could also be due to differences in mean storm-track characteristics over the North Pacific and North Atlantic.
  • Preprint
    Silver hake tracks changes in Northwest Atlantic circulation
    ( 2011-07) Nye, Janet A. ; Joyce, Terrence M. ; Kwon, Young-Oh ; Link, Jason S.
    Recent studies documenting shifts in spatial distribution of many organisms in response to a warming climate highlight the need to understand the mechanisms underlying species distribution at large spatial scales. Here we present one noteworthy example of remote oceanographic processes governing the spatial distribution of adult silver hake, Merluccius bilinearis, a commercially important fish in the Northeast US shelf region. Changes in spatial distribution of silver hake over the last 40 years are highly correlated with the position of the Gulf Stream (GS). These changes in distribution are in direct response to local changes in bottom temperature on the continental shelf that are responding to the same large scale circulation change affecting the GS path, namely changes in the Atlantic Meridional Overturning Circulation (AMOC). If AMOC weakens as is suggested by global climate models, silver hake distribution will remain in a poleward position, the extent to which could be forecast at both decadal and multidecadal scales.
  • Article
    Observational needs supporting marine ecosystems modeling and forecasting: from the global ocean to regional and coastal systems
    (Frontiers Media, 2019-10-15) Capotondi, Antonietta ; Jacox, Michael ; Bowler, Chris ; Kavanaugh, Maria T. ; Lehodey, Patrick ; Barrie, Daniel ; Brodie, Stephanie ; Chaffron, Samuel ; Cheng, Wei ; Dias, Daniela F. ; Eveillard, Damien ; Guidi, Lionel ; Iudicone, Daniele ; Lovenduski, Nicole S. ; Nye, Janet A. ; Ortiz, Ivonne ; Pirhalla, Douglas ; Pozo Buil, Mercedes ; Saba, Vincent S. ; Sheridan, Scott ; Siedlecki, Samantha A. ; Subramanian, Aneesh C. ; de Vargas, Colomban ; Di Lorenzo, Emanuele ; Doney, Scott C. ; Hermann, Albert J. ; Joyce, Terrence M. ; Merrifield, Mark ; Miller, Arthur J. ; Not, Fabrice ; Pesant, Stephane
    Many coastal areas host rich marine ecosystems and are also centers of economic activities, including fishing, shipping and recreation. Due to the socioeconomic and ecological importance of these areas, predicting relevant indicators of the ecosystem state on sub-seasonal to interannual timescales is gaining increasing attention. Depending on the application, forecasts may be sought for variables and indicators spanning physics (e.g., sea level, temperature, currents), chemistry (e.g., nutrients, oxygen, pH), and biology (from viruses to top predators). Many components of the marine ecosystem are known to be influenced by leading modes of climate variability, which provide a physical basis for predictability. However, prediction capabilities remain limited by the lack of a clear understanding of the physical and biological processes involved, as well as by insufficient observations for forecast initialization and verification. The situation is further complicated by the influence of climate change on ocean conditions along coastal areas, including sea level rise, increased stratification, and shoaling of oxygen minimum zones. Observations are thus vital to all aspects of marine forecasting: statistical and/or dynamical model development, forecast initialization, and forecast validation, each of which has different observational requirements, which may be also specific to the study region. Here, we use examples from United States (U.S.) coastal applications to identify and describe the key requirements for an observational network that is needed to facilitate improved process understanding, as well as for sustaining operational ecosystem forecasting. We also describe new holistic observational approaches, e.g., approaches based on acoustics, inspired by Tara Oceans or by landscape ecology, which have the potential to support and expand ecosystem modeling and forecasting activities by bridging global and local observations.
  • Technical Report
    Observations of the Antarctic polar front during FDRAKE 76 : a cruise report
    (Woods Hole Oceanographic Institution, 1976-11) Joyce, Terrence M. ; Dean, Jerome P. ; McCartney, Michael S. ; Millard, Robert C. ; Moller, Donald A. ; Voorhis, A. ; Dahm, C. ; Georgi, Daniel T. ; Kullenberg, G. ; Toole, John M. ; Zenk, Walter
    During March/April 1976 the small-scale structure of the Antarctic Polar Front was observed in the Drake Passage. The observations were part of the International Southern Ocean Studies (ISOS) program called FDRAke 76. The purpose of the program was to obtain densely sampled measurements of temperature, salinity, dissolved oxygen, and chemical nutrients in the Polar Front Zone (PFZ) and pilot measurements of horizontal and vertical velocities in order to explain the above scalar variability. The PFZ is a region where Antarctic and sub-Antarctic waters intermingle and presumably mix to affect the properties of Antarctic Intermediate Water. A report on the third leg of Cruise 107 of the R. V. THOMPSON is presented as well as a description of the measurements and a preliminary report of the data. A feature of interest is the pinching off of a northward meander of the circumpolar current system into a cyclonic ring of Antarctic Waters.
  • Article
    Zonal circulation across 52°W in the North Atlantic
    (American Geophysical Union, 2004-11-18) Hall, Melinda M. ; Joyce, Terrence M. ; Pickart, Robert S. ; Smethie, William M. ; Torres, Daniel J.
    In July–August 1997, a hydrographic/Acoustic Doppler Current Profiler (ADCP)/tracer section was occupied along 52°W in the North Atlantic as part of the World Ocean Circulation Experiment Hydrographic Program. Underway and lowered ADCP (LADCP) data have been used to reference geostrophic velocities calculated from the hydrographic data; additional (small) velocity adjustments provided by an inverse model, constraining mass and silicate transports in 17 neutral density layers, yield the absolute zonal velocity field for 52°W. We find a vigorous circulation throughout the entire section, with an unusually strong Gulf Stream (169 Sv) and southern Deep Western Boundary Current (DWBC; 64 Sv) at the time of the cruise. At the northern boundary, on the west side of the Grand Banks of Newfoundland, we find the westward flowing Labrador Current (8.6 Sv), whose continuity from the Labrador Sea, east of our section, has been disputed. Directly to the south we identify the slopewater current (12.5 Sv eastward) and northern DWBC (12.5 Sv westward). Strong departures from strictly zonal flow in the interior, which are found in the LADCP data, make it difficult to diagnose the circulation there. Isolated deep property extrema in the southern portion, associated with alternating bands of eastward and westward flow, are consistent with the idea that the rough topography of the Mid-Atlantic Ridge, directly east of our section, causes enhanced mixing of Antarctic Bottom Water properties into overlying waters with distinctly different properties. We calculate heat and freshwater fluxes crossing 52°W that exceed estimates based on air-sea exchanges by a factor of 1.7.
  • Article
    Subduction on the northern and southern flanks of the Gulf Stream
    (American Meteorological Society, 2010-02) Thomas, Leif N. ; Joyce, Terrence M.
    Sections of temperature, salinity, dissolved oxygen, and velocity were made crossing the Gulf Stream in late January 2006 to investigate the role of frontal processes in the formation of Eighteen Degree Water (EDW), the Subtropical Mode Water of the North Atlantic. The sections were nominally perpendicular to the stream and measured in a Lagrangian frame by following a floating spar buoy drifting in the Gulf Stream’s warm core. During the survey, EDW was isolated from the mixed layer by the stratified seasonal pycnocline, suggesting that EDW was not yet actively being formed at this time in the season and at the longitudes over which the survey was conducted (64°–70°W). However, in two of the sections, the seasonal pycnocline in the core of the Gulf Stream was broken by an intrusion of cold, fresh, weakly stratified water, nearly saturated in oxygen, that appears to have been subducted from the surface mixed layer north of the stream. The intrusion was identified in three of the sections in profiles with a nearly identical temperature–salinity relation. From the western-to-easternmost sections, where the intrusion was observed, the depth of the intrusion’s salinity minimum descended by 90 m in the 71 h it took to complete this part of the survey. This apparent subduction occurred primarily on the upstream side of a meander trough, where the cross-stream velocity was confluent and frontogenetic. Using a variant of the omega equation, the vertical velocity driven by the confluent flow was inferred and yielded downwelling in the vicinity of the intrusion spanning 10–40 m day−1, a range of values consistent with the intrusion’s observed descent, suggesting that frontal subduction was responsible for the formation of the intrusion. In the easternmost section located downstream of the meander trough, the flow was diffluent, driving an inferred vertical circulation that was of the opposite sense to that in the section upstream of the trough. In transiting the two sides of the trough, the intrusion was observed to move toward the center of the stream between the downwelling branches of the opposing vertical circulations, resulting in a downward Lagrangian mean vertical velocity and net subduction. Hydrographic evidence of the subduction of weakly stratified surface waters was seen in the southern flank of the Gulf Stream as well. The solution of the omega equation suggests that this subduction was associated with a relatively shallow vertical circulation confined to the upper 200 m of the water column in the proximity of the front marking the southern edge of the warm core.
  • Article
    On the predominant nonlinear response of the extratropical atmosphere to meridional shifts of the Gulf Stream
    (American Meteorological Society, 2017-11-07) Seo, Hyodae ; Kwon, Young-Oh ; Joyce, Terrence M. ; Ummenhofer, Caroline C.
    The North Atlantic atmospheric circulation response to the meridional shifts of the Gulf Stream (GS) path is examined using a large ensemble of high-resolution hemispheric-scale Weather Research and Forecasting Model simulations. The model is forced with a broad range of wintertime sea surface temperature (SST) anomalies derived from a lag regression on a GS index. The primary result of the model experiments, supported in part by an independent analysis of a reanalysis dataset, is that the large-scale quasi-steady North Atlantic circulation response is remarkably nonlinear about the sign and amplitude of the SST anomaly chosen over a wide range of GS shift scenarios. The nonlinear response prevails over the weak linear response and resembles the negative North Atlantic Oscillation (NAO), the leading intrinsic mode of variability in the model and the observations. Further analysis of the associated dynamics reveals that the nonlinear responses are accompanied by the shift of the North Atlantic eddy-driven jet, which is reinforced, with nearly equal importance, by the high-frequency transient eddy feedback and the low-frequency wave-breaking events. Additional sensitivity simulations confirm that the nonlinearity of the circulation response is a robust feature found over the broad parameter space encompassing not only the varied SST but also the absence/presence of tropical influence, the varying lateral boundary conditions, and the initialization scheme. The result highlights the fundamental importance of the intrinsically nonlinear transient eddy dynamics and the eddy–mean flow interactions in generating the nonlinear downstream response to the meridional shifts in the Gulf Stream.
  • Article
    On the path of the Gulf Stream and the Atlantic meridional overturning circulation
    (American Meteorological Society, 2010-06-01) Joyce, Terrence M. ; Zhang, Rong
    The Atlantic meridional overturning circulation (AMOC) simulated in various ocean-only and coupled atmosphere–ocean numerical models often varies in time because of either forced or internal variability. The path of the Gulf Stream (GS) is one diagnostic variable that seems to be sensitive to the amplitude of the AMOC, yet previous modeling studies show a diametrically opposed relationship between the two variables. In this note this issue is revisited, bringing together ocean observations and comparisons with the GFDL Climate Model version 2.1 (CM2.1), both of which suggest a more southerly (northerly) GS path when the AMOC is relatively strong (weak). Also shown are some examples of possible diagnostics to compare various models and observations on the relationship between shifts in GS path and changes in AMOC strength in future studies.