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  • Coupled models  (15)
  • Sea surface temperature  (15)
  • Wind stress  (13)
  • American Meteorological Society  (33)
  • 2010-2014  (33)
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  • 1
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 1486–1500, doi:10.1175/2007JPO3767.1.
    Description: Fits of an annual harmonic to depth-average along-shelf current time series longer than 200 days from 27 sites over the Middle Atlantic Bight (MAB) continental shelf have amplitudes of a few centimeters per second. These seasonal variations are forced by seasonal variations in the wind stress and the cross-shelf density gradient. The component of wind stress that drives the along-shelf flow over most of the MAB mid- and outer shelf is oriented northeast–southwest, perpendicular to the major axis of the seasonal variation in the wind stress. Consequently, there is not a significant seasonal variation in the wind-driven along-shelf flow, except over the southern MAB shelf and the inner shelf of New England where the wind stress components forcing the along-shelf flow are north–south and east–west, respectively. The seasonal variation in the residual along-shelf flow, after removing the wind-driven component, has an amplitude of a few centimeters per second with maximum southwestward flow in spring onshore of the 60-m isobath and autumn offshore of the 60-m isobath. The spring maximum onshore of the 60-m isobath is consistent with the maximum river discharges in spring enhancing cross-shelf salinity gradients. The autumn maximum offshore of the 60-m isobath and a steady phase increase with water depth offshore of Cape Cod are both consistent with the seasonal variation in the cross-shelf temperature gradient associated with the development and destruction of a near-bottom pool of cold water over the mid and outer shelf (“cold pool”) due to seasonal variations in surface heat flux and wind stress.
    Description: This research was funded by the Ocean Sciences Division of the National Science Foundation under Grants OCE-820773, OCE-841292, and OCE- 848961.
    Keywords: Seasonal variability ; Ocean circulation ; Continental shelf ; Wind stress ; Density currents
    Repository Name: Woods Hole Open Access Server
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  • 2
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 20 (2007): 2416-2433, doi:10.1175/JCLI4103.1.
    Description: North Pacific decadal oceanic and atmospheric variability is examined from a 650-yr control integration of the Community Climate System Model version 2. The dominant pattern of winter sea surface temperature (SST) variability is similar to the observed “Pacific decadal oscillation,” with maximum amplitude along the Kuroshio Extension. SST anomalies in this region exhibit significant spectral peaks at approximately 16 and 40 yr. Lateral geostrophic heat flux divergence, caused by a meridional shift of the Kuroshio Extension forced by basin-scale wind stress curl anomalies 3–5 yr earlier, is responsible for the decadal SST variability; local surface heat flux and Ekman heat flux divergence act as a damping and positive feedback, respectively. A simple linear Rossby wave model is invoked to explicitly demonstrate the link between the wind stress curl forcing and decadal variability in the Kuroshio Extension. The Rossby wave model not only successfully reproduces the two decadal spectral peaks, but also illustrates that only the low-frequency (〉10-yr period) portion of the approximately white noise wind stress curl forcing is relevant. This model also demonstrates that the weak and insignificant decadal spectral peaks in the wind stress curl forcing are necessary for producing the corresponding strong and significant oceanic peaks in the Kuroshio Extension. The wind stress curl response to decadal SST anomalies in the Kuroshio Extension is similar in structure but opposite in sign and somewhat weaker than the wind stress curl forcing pattern. These results suggest that the simulated North Pacific decadal variability owes its existence to two-way ocean–atmosphere coupling.
    Description: The first author gratefully acknowledges financial support from NOAA’s Office of Global Programs (grant to C. Deser) and the CCSM Project Office.
    Keywords: Decadal variability ; Fluxes ; Rossby waves ; Wind stress ; Coupled models
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  • 3
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 20 (2007): 2760-2768, doi:10.1175/JCLI4138a.1
    Description: The correlation between parameters characterizing observed westerly wind bursts (WWBs) in the equatorial Pacific and the large-scale SST is analyzed using singular value decomposition. The WWB parameters include the amplitude, location, scale, and probability of occurrence for a given SST distribution rather than the wind stress itself. This approach therefore allows for a nonlinear relationship between the SST and the wind signal of the WWBs. It is found that about half of the variance of the WWB parameters is explained by only two large-scale SST modes. The first mode represents a developed El Niño event, while the second mode represents the seasonal cycle. More specifically, the central longitude of WWBs, their longitudinal extent, and their probability seem to be determined to a significant degree by the ENSO-driven signal. The amplitude of the WWBs is found to be strongly influenced by the phase of the seasonal cycle. It is concluded that the WWBs, while partially stochastic, seem an inherent part of the large-scale deterministic ENSO dynamics. Implications for ENSO predictability and prediction are discussed.
    Description: Eli Tziperman is supported by the U.S. National Science Foundation Climate Dynamics Program Grant ATM- 0351123 and by the McDonnell Foundation. Lisan Yu is supported by the NASA Ocean Vector Wind Science Team under JPL Contract 1216955 and NSF Climate Dynamics Grant ATM-0350266.
    Keywords: Sea surface temperature ; Wind bursts ; Tropics ; Pacific Ocean
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  • 4
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 20 (2007): 3785–3801, doi:10.1175/JCLI4234.1
    Description: The influences of strong gradients in sea surface temperature on near-surface cross-front winds are explored in a series of idealized numerical modeling experiments. The atmospheric model is the Naval Research Laboratory Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) model, which is fully coupled to the Regional Ocean Modeling System (ROMS) ocean model. A series of idealized, two-dimensional model calculations is carried out in which the wind blows from the warm-to-cold side or the cold-to-warm side of an initially prescribed ocean front. The evolution of the near-surface winds, boundary layer, and thermal structure is described, and the balances in the momentum equation are diagnosed. The changes in surface winds across the front are consistent with previous models and observations, showing a strong positive correlation with the sea surface temperature and boundary layer thickness. The coupling arises mainly as a result of changes in the flux Richardson number across the front, and the strength of the coupling coefficient grows quadratically with the strength of the cross-front geostrophic wind. The acceleration of the winds over warm water results primarily from the rapid change in turbulent mixing and the resulting unbalanced Coriolis force in the vicinity of the front. Much of the loss/gain of momentum perpendicular to the front in the upper and lower boundary layer results from acceleration/deceleration of the flow parallel to the front via the Coriolis term. This mechanism is different from the previously suggested processes of downward mixing of momentum and adjustment to the horizontal pressure gradient, and is active for flows off the equator with sufficiently strong winds. Although the main focus of this work is on the midlatitude, strong wind regime, calculations at low latitudes and with weak winds show that the pressure gradient and turbulent mixing terms dominate the cross-front momentum budget, consistent with previous work.
    Description: This work was supported by the Office of Naval Research Grant N00014-05-1-0300.
    Keywords: Fronts ; Sea surface temperature ; Wind stress ; Coupled models ; Boundary layer
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  • 5
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 40 (2010): 2743–2756, doi:10.1175/2010JPO4339.1.
    Description: Analysis of modern and historical observations demonstrates that the temperature of the intermediate-depth (150–900 m) Atlantic water (AW) of the Arctic Ocean has increased in recent decades. The AW warming has been uneven in time; a local 1°C maximum was observed in the mid-1990s, followed by an intervening minimum and an additional warming that culminated in 2007 with temperatures higher than in the 1990s by 0.24°C. Relative to climatology from all data prior to 1999, the most extreme 2007 temperature anomalies of up to 1°C and higher were observed in the Eurasian and Makarov Basins. The AW warming was associated with a substantial (up to 75–90 m) shoaling of the upper AW boundary in the central Arctic Ocean and weakening of the Eurasian Basin upper-ocean stratification. Taken together, these observations suggest that the changes in the Eurasian Basin facilitated greater upward transfer of AW heat to the ocean surface layer. Available limited observations and results from a 1D ocean column model support this surmised upward spread of AW heat through the Eurasian Basin halocline. Experiments with a 3D coupled ice–ocean model in turn suggest a loss of 28–35 cm of ice thickness after 50 yr in response to the 0.5 W m−2 increase in AW ocean heat flux suggested by the 1D model. This amount of thinning is comparable to the 29 cm of ice thickness loss due to local atmospheric thermodynamic forcing estimated from observations of fast-ice thickness decline. The implication is that AW warming helped precondition the polar ice cap for the extreme ice loss observed in recent years.
    Description: This study was supported by JAMSTEC (IP and VI), NOAA (IP, VI, and ID), NSF (IP,VA,VI, ID, JT, andMS),NASA(IP andVI), BMBF (ID), and UK NERC (SB) grants.
    Keywords: Arctic ; Forcing ; Temperature ; Sea ice ; Heating ; Coupled models
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  • 6
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 41 (2011): 1741–1755, doi:10.1175/2011JPO4437.1.
    Description: An in-depth data analysis was conducted to understand the occurrence of a strong sea surface temperature (SST) front in the central Bay of Bengal before the formation of Cyclone Nargis in April 2008. Nargis changed its course after encountering the front and tracked along the front until making landfall. One unique feature of this SST front was its coupling with high sea surface height anomalies (SSHAs), which is unusual for a basin where SST is normally uncorrelated with SSHA. The high SSHAs were associated with downwelling Rossby waves, and the interaction between downwelling and surface fresh waters was a key mechanism to account for the observed SST–SSHA coupling. The near-surface salinity field in the bay is characterized by strong stratification and a pronounced horizontal gradient, with low salinity in the northeast. During the passage of downwelling Rossby waves, freshening of the surface layer was observed when surface velocities were southwestward. Horizontal convergence of freshwater associated with downwelling Rossby waves increased the buoyancy of the upper layer and caused the mixed layer to shoal to within a few meters of the surface. Surface heating trapped in the thin mixed layer caused the fresh layer to warm, whereas the increase in buoyancy from low-salinity waters enhanced the high SSHA associated with Rossby waves. Thus, high SST coincided with high SSHA. The dominant role of salinity in controlling high SSHA suggests that caution should be exercised when computing hurricane heat potential in the bay from SSHA. This situation is different from most tropical oceans, where temperature has the dominant effect on SSHA.
    Description: This work was supported by the NOAA/Office of Climate Observation (OCO) program.
    Keywords: Rossby waves ; Sea surface temperature ; Sea/ocean surface
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  • 7
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 5153–5172, doi:10.1175/JCLI-D-11-00463.1.
    Description: Atlantic meridional overturning circulation (AMOC) variability is documented in the Community Climate System Model, version 4 (CCSM4) preindustrial control simulation that uses nominal 1° horizontal resolution in all its components. AMOC shows a broad spectrum of low-frequency variability covering the 50–200-yr range, contrasting sharply with the multidecadal variability seen in the T85 × 1 resolution CCSM3 present-day control simulation. Furthermore, the amplitude of variability is much reduced in CCSM4 compared to that of CCSM3. Similarities as well as differences in AMOC variability mechanisms between CCSM3 and CCSM4 are discussed. As in CCSM3, the CCSM4 AMOC variability is primarily driven by the positive density anomalies at the Labrador Sea (LS) deep-water formation site, peaking 2 yr prior to an AMOC maximum. All processes, including parameterized mesoscale and submesoscale eddies, play a role in the creation of salinity anomalies that dominate these density anomalies. High Nordic Sea densities do not necessarily lead to increased overflow transports because the overflow physics is governed by source and interior region density differences. Increased overflow transports do not lead to a higher AMOC either but instead appear to be a precursor to lower AMOC transports through enhanced stratification in LS. This has important implications for decadal prediction studies. The North Atlantic Oscillation (NAO) is significantly correlated with the positive boundary layer depth and density anomalies prior to an AMOC maximum. This suggests a role for NAO through setting the surface flux anomalies in LS and affecting the subpolar gyre circulation strength.
    Description: The CCSM project is supported by NSF and the Office of Science (BER) of the U.S. Department of Energy. SGY and YOK were supported by the NOAA Climate Program Office under Climate Variability and Predictability Program Grants NA09OAR4310163 and NA10OAR4310202, respectively.
    Description: 2013-02-01
    Keywords: Meridional overturning circulation ; Coupled models ; Ocean models ; Oceanic variability
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  • 8
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 2234–2253, doi:10.1175/JPO-D-12-033.1.
    Description: Meridional velocity, mass, and heat transport in the equatorial oceans are difficult to estimate because of the nonapplicability of the geostrophic balance. For this purpose a steady-state model is utilized in the equatorial Indian Ocean using NCEP wind stress and temperature and salinity data from the World Ocean Atlas 2005 (WOA05) and Argo. The results show a Somali Current flowing to the south during the winter monsoon carrying −11.5 ± 1.3 Sv (1 Sv ≡ 106 m3 s−1) and −12.3 ± 0.3 Sv from WOA05 and Argo, respectively. In the summer monsoon the Somali Current reverses to the north transporting 16.8 ± 1.2 Sv and 19.8 ± 0.6 Sv in the WOA05 and Argo results. Transitional periods are considered together and in consequence, there is not a clear Somali Current present in this period. Model results fit with in situ measurements made around the region, although Argo data results are quite more realistic than WOA05 data results.
    Description: This study has been partly funded by the MOC Project (CTM 2008- 06438) and the Spanish contribution to the Argo network (AC2009 ACI2009-0998), financed by the Spanish Government and Feder.
    Description: 2013-06-01
    Keywords: Indian Ocean ; Subtropics ; Currents ; Ocean circulation ; Transport ; Wind stress
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  • 9
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 1589–1610, doi:10.1175/JPO-D-12-0173.1.
    Description: This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations of the surface roughness and drag coefficient used to estimate the surface stress from bulk formulas. Specifically, the Coupled Ocean–Atmosphere Response Experiment (COARE) 3.0 bulk flux algorithm is refined to create COARE 3.5. Oversea measurements of dimensionless shear are used to investigate the stability function under stable and convective conditions. The behavior of surface roughness is then investigated over a wider range of wind speeds (up to 25 m s−1) and wave conditions than have been available from previous oversea field studies. The wind speed dependence of the Charnock coefficient α in the COARE algorithm is modified to , where m = 0.017 m−1 s and b = −0.005. When combined with a parameterization for smooth flow, this formulation gives better agreement with the stress estimates from all of the field programs at all winds speeds with significant improvement for wind speeds over 13 m s−1. Wave age– and wave slope–dependent parameterizations of the surface roughness are also investigated, but the COARE 3.5 wind speed–dependent formulation matches the observations well without any wave information. The available data provide a simple reason for why wind speed–, wave age–, and wave slope–dependent formulations give similar results—the inverse wave age varies nearly linearly with wind speed in long-fetch conditions for wind speeds up to 25 m s−1.
    Description: This work was funded by the National Science Foundation Grant OCE04-24536 as part of the CLIVAR Mode Water Dynamics Experiment (CLIMODE) and the Office of Naval Research Grant N00014-05-1-0139 as part of the CBLAST-LOW program.
    Description: 2014-02-01
    Keywords: Wind shear ; Wind stress ; Atmosphere-ocean interaction ; Fluxes ; Momentum ; Algorithms
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  • 10
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 909–917, doi:10.1175/2007JPO3535.1.
    Description: The classical two-box model of Stommel is extended in two directions: replacing the buoyancy constraint with an energy constraint and including the wind-driven gyre. Stommel postulated a buoyancy constraint for the thermohaline circulation, and his basic idea has evolved into the dominating theory of thermohaline circulation; however, recently, it is argued that the thermohaline circulation is maintained by mechanical energy from wind stress and tides. The major difference between these two types of models is the bifurcation structure: the Stommel-like model has two thermal modes (one stable and another one unstable) and one stable haline mode, whereas the energy-constraint model has one stable thermal mode and two saline modes (one stable and another one unstable). Adding the wind-driven gyre changes the threshold value of thermohaline bifurcation greatly; thus, the inclusion of the wind-driven gyre is a vital step in completely modeling the physical processes related to thermohaline circulation.
    Description: YPG was supported by the National Science Foundation of China (NSFC, 40676022), the National Basic Research Program of China (2006CB403605), and the Guangdong Natural Science Foundation (5003672). RXH was supported by the National Oceanic and Atmospheric Administration through CICOR Cooperative Agreement NA17RJ1223 to the Woods Hole Oceanographic Institution.
    Keywords: Thermohaline circulation ; Mixing ; Wind stress ; Buoyancy ; Energy budget
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  • 11
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 2164–2184, doi:10.1175/2008JPO3962.1.
    Description: This is the second part of a two-part investigation of a coupled wind and wave model that includes the enhanced form drag of breaking waves. The model is based on the wave energy balance and the conservation of air-side momentum and energy. In Part I, coupled nonlinear advance–delay differential equations were derived, which govern the wave height spectrum, the distribution of breaking waves, and vertical air side profiles of the turbulent stress and wind speed. Numeric solutions were determined for mature seas. Here, numeric solutions for a wide range of wind and wave conditions are obtained, including young, strongly forced wind waves. Furthermore, the “spatial sheltering effect” is introduced so that smaller waves in airflow separation regions of breaking longer waves cannot be forced by the wind. The solutions strongly depend on the wave height curvature spectrum at high wavenumbers (the “threshold saturation level”). As the threshold saturation level is reduced, the effect of breaking waves becomes stronger. For young strongly forced waves (laboratory conditions), breaking waves close to the spectral peak dominate the wind input and previous solutions of a model with only input to breaking waves are recovered. Model results of the normalized roughness length are generally consistent with previous laboratory and field measurements. For field conditions, the wind stress depends sensitively on the wave height spectrum. The spatial sheltering may modify the number of breaking shorter waves, in particular, for younger seas.
    Description: This work was supported by the U.S. National Science Foundation (Grant OCE- 0526177) and the U.S. Office of Naval Research (Grant N00014–06–10729).
    Keywords: Wave breaking ; Coupled models ; Wind stress ; Momentum ; Sea state
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  • 12
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 20 (2007): 3395-3410, doi:10.1175/JCLI4195.1
    Description: Using 40-yr ECMWF Re-Analysis (ERA-40) data and in situ observations, the positive trend of Southern Ocean surface wind stress during two recent decades is detected, and its close linkage with spring Antarctic ozone depletion is established. The spring Antarctic ozone depletion affects the Southern Hemisphere lower-stratospheric circulation in late spring/early summer. The positive feedback involves the strengthening and cooling of the polar vortex, the enhancement of meridional temperature gradients and the meridional and vertical potential vorticity gradients, the acceleration of the circumpolar westerlies, and the reduction of the upward wave flux. This feedback loop, together with the ozone-related photochemical interaction, leads to the upward tendency of lower-stratospheric zonal wind in austral summer. In addition, the stratosphere–troposphere coupling, facilitated by ozone-related dynamics and the Southern Annular Mode, cooperates to relay the zonal wind anomalies to the upper troposphere. The wave–mean flow interaction and the meridional circulation work together in the form of the Southern Annular Mode, which transfers anomalous wind signals downward to the surface, triggering a striking strengthening of surface wind stress over the Southern Ocean.
    Description: This study was supported by MOST of China (Grant 2006CB403604) and Chinese Academy of Sciences (Grant KZSW2-YW-214) (for YXY and DXW) and W. Alan Clark Chair from Woods Hole Oceanographic Institution (for RXH).
    Keywords: Wind stress ; Decadal variability ; Ozone ; Southern Ocean ; Stratospheric circulation
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  • 13
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 37 (2007): 1103-1121, doi:10.1175/jpo3041.1.
    Description: The role of mesoscale oceanic eddies is analyzed in a quasigeostrophic coupled ocean–atmosphere model operating at a large Reynolds number. The model dynamics are characterized by decadal variability that involves nonlinear adjustment of the ocean to coherent north–south shifts of the atmosphere. The oceanic eddy effects are diagnosed by the dynamical decomposition method adapted for nonstationary external forcing. The main effects of the eddies are an enhancement of the oceanic eastward jet separating the subpolar and subtropical gyres and a weakening of the gyres. The flow-enhancing effect is due to nonlinear rectification driven by fluctuations of the eddy forcing. This is a nonlocal process involving generation of the eddies by the flow instabilities in the western boundary current and the upstream part of the eastward jet. The eddies are advected by the mean current to the east, where they backscatter into the rectified enhancement of the eastward jet. The gyre-weakening effect, which is due to the time-mean buoyancy component of the eddy forcing, is a result of the baroclinic instability of the westward return currents. The diagnosed eddy forcing is parameterized in a non-eddy-resolving ocean model, as a nonstationary random process, in which the corresponding parameters are derived from the control coupled simulation. The key parameter of the random process—its variance—is related to the large-scale flow baroclinicity index. It is shown that the coupled model with the non-eddy-resolving ocean component and the parameterized eddies correctly simulates climatology and low-frequency variability of the control eddy-resolving coupled solution.
    Description: Funding for this work came from NSF Grants OCE 02-221066 and OCE 03-44094. Additional funding for PB was provided by the U.K. Royal Society Fellowship and by WHOI Grants 27100056 and 52990035.
    Keywords: Ocean dynamics ; Ocean models ; Eddies ; Jets ; Coupled models
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  • 14
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 37 (2007): 1092–1097, doi:10.1175/JPO3045.1.
    Description: The impact of the observed relationship between sea surface temperature and surface wind stress on baroclinic instability in the ocean is explored using linear theory and a nonlinear model. A simple parameterization of the influence of sea surface temperature on wind stress is used to derive a surface boundary condition for the vertical velocity at the base of the oceanic Ekman layer. This boundary condition is applied to the classic linear, quasigeostrophic stability problem for a uniformly sheared flow originally studied by Eady in the 1940s. The results demonstrate that for a wind directed from warm water toward cold water, the coupling acts to enhance the growth rate, and increase the wavelength, of the most unstable wave. Winds in the opposite sense reduce the growth rate and decrease the wavelength of the most unstable wave. For representative coupling strengths, the change in growth rate can be as large as ±O(50%). This effect is largest for shallow, strongly stratified, low-latitude flows.
    Description: This work was supported by the Office of Naval Research Grant N00014-05-1-0300.
    Keywords: Wind stress ; Instability ; Sea surface temperature ; Baroclinic flows ; Ocean dynamics
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  • 15
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2006. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 19 (2006): 6153–6169, doi:10.1175/JCLI3970.1.
    Description: The present study used a new net surface heat flux (Qnet) product obtained from the Objective Analyzed Air–Sea Fluxes (OAFlux) project and the International Satellite Cloud Climatology Project (ISCCP) to examine two specific issues—one is to which degree Qnet controls seasonal variations of sea surface temperature (SST) in the tropical Atlantic Ocean (20°S–20°N, east of 60°W), and the other is whether the physical relation can serve as a measure to evaluate the physical representation of a heat flux product. To better address the two issues, the study included the analysis of three additional heat flux products: the Southampton Oceanographic Centre (SOC) heat flux analysis based on ship reports, and the model fluxes from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis and the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). The study also uses the monthly subsurface temperature fields from the World Ocean Atlas to help analyze the seasonal changes of the mixed layer depth (hMLD). The study showed that the tropical Atlantic sector could be divided into two regimes based on the influence level of Qnet. SST variability poleward of 5°S and 10°N is dominated by the annual cycle of Qnet. In these regions the warming (cooling) of the sea surface is highly correlated with the increased (decreased) Qnet confined in a relatively shallow (deep) hMLD. The seasonal evolution of SST variability is well predicted by simply relating the local Qnet with a variable hMLD. On the other hand, the influence of Qnet diminishes in the deep Tropics within 5°S and 10°N and ocean dynamic processes play a dominant role. The dynamics-induced changes in SST are most evident along the two belts, one of which is located on the equator and the other off the equator at about 3°N in the west, which tilts to about 10°N near the northwestern African coast. The study also showed that if the degree of consistency between the correlation relationships of Qnet, hMLD, and SST variability serves as a measure of the quality of the Qnet product, then the Qnet from OAFlux + ISCCP and ERA-40 are most physically representative, followed by SOC. The NCEP–NCAR Qnet is least representative. It should be noted that the Qnet from OAFlux + ISCCP and ERA-40 have a quite different annual mean pattern. OAFlux + ISCCP agrees with SOC in that the tropical Atlantic sector gains heat from the atmosphere on the annual mean basis, where the ERA-40 and the NCEP–NCAR model reanalyses indicate that positive Qnet occurs only in the narrow equatorial band and in the eastern portion of the tropical basin. Nevertheless, seasonal variances of the Qnet from OAFlux + ISCCP and ERA-40 are very similar once the respective mean is removed, which explains why the two agree with each other in accounting for the seasonal variability of SST. In summary, the study suggests that an accurate estimation of surface heat flux is crucially important for understanding and predicting SST fluctuations in the tropical Atlantic Ocean. It also suggests that future emphasis on improving the surface heat flux estimation should be placed more on reducing the mean bias.
    Description: This study is support by the NOAA CLIVAR Atlantic under Grant NA06GP0453 and NOAA Climate observations and Climate Change and Data Detection under Grant NA17RJ1223.
    Keywords: Sea surface temperature ; Surface fluxes ; Seasonal variability
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  • 16
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 343–349, doi:10.1175/JCLI-D-11-00059.1.
    Description: The Equatorial Undercurrent (EUC) is a major component of the tropical Pacific Ocean circulation. EUC velocity in most global climate models is sluggish relative to observations. Insufficient ocean resolution slows the EUC in the eastern Pacific where nonlinear terms should dominate the zonal momentum balance. A slow EUC in the east creates a bottleneck for the EUC to the west. However, this bottleneck does not impair other major components of the tropical circulation, including upwelling and poleward transport. In most models, upwelling velocity and poleward transport divergence fall within directly estimated uncertainties. Both of these transports play a critical role in a theory for how the tropical Pacific may change under increased radiative forcing, that is, the ocean dynamical thermostat mechanism. These findings suggest that, in the mean, global climate models may not underrepresent the role of equatorial ocean circulation, nor perhaps bias the balance between competing mechanisms for how the tropical Pacific might change in the future. Implications for model improvement under higher resolution are also discussed.
    Description: KBK gratefully acknowledges the J. Lamar Worzel Assistant Scientist Fund. GCJ is supported by NOAA’s Office of Oceanic and Atmospheric Research. RM gratefully acknowledges the generous support and hospitality of the Divecha Centre for Climate Change and CAOS at IISc, Bangalore, and partial support by NASA PO grants.
    Description: 2012-07-01
    Keywords: Tropics ; Ocean circulation ; Ocean dynamics ; Climate models ; Coupled models ; Ocean models
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  • 17
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 40 (2010): 1004-1017, doi:10.1175/2009JPO4300.1.
    Description: Sea surface temperature variations along the entire U.S. East Coast from 1875 to 2007 are characterized using a collection of historical observations from lighthouses and lightships combined with recent buoy and shore-based measurements. Long-term coastal temperature trends are warming in the Gulf of Maine [1.0° ± 0.3°C (100 yr)−1] and Middle Atlantic Bight [0.7° ± 0.3°C (100 yr)−1], whereas trends are weakly cooling or not significant in the South Atlantic Bight [−0.1° ± 0.3°C (100 yr)−1] and off Florida [−0.3° ± 0.2°C (100 yr)−1]. Over the last century, temperatures along the northeastern U.S. coast have warmed at a rate 1.8–2.5 times the regional atmospheric temperature trend but are comparable to warming rates for the Arctic and Labrador, the source of coastal ocean waters north of Cape Hatteras (36°N). South of Cape Hatteras, coastal ocean temperature trends match the regional atmospheric temperature trend. The observations and a simple model show that along-shelf transport, associated with the mean coastal current system running from Labrador to Cape Hatteras, is the mechanism controlling long-term temperature changes for this region and not the local air–sea exchange of heat.
    Description: This work was supported by NSF Grant OCE-0220773.
    Keywords: Sea surface temperature
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  • 18
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    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 26 (2009): 1867-1890, doi:10.1175/2009JTECHO667.1.
    Description: The accuracies of the meteorological sensors (air temperature, relative humidity, barometric pressure, near-surface temperature, longwave and shortwave radiation, and wind speed and direction) that compose the Improved Meteorological (IMET) system used on buoys at long-term ocean time series sites known as ocean reference stations (ORS) are analyzed to determine their absolute error characteristics. The predicted errors are compared to in situ measurement discrepancies and other observations (direct flux shipboard sensors) to confirm the predictions. The meteorological errors are then propagated through bulk flux formulas and the Coupled Ocean–Atmosphere Response Experiment (COARE) algorithm to give predicted errors for the heat flux components, the freshwater flux, and the momentum flux. Absolute errors are presented for three frequency bands [instantaneous (1-min sampling), diurnal, and annual]. The absolute uncertainty in the annually averaged net heat flux is found to be 8 W m−2 for conditions similar to the current ORS deployments in the subtropics.
    Description: Support for the buoy deployments and the analysis from the NOAA Climate Observation Program is greatly appreciated (Grants NA17RJ1223 and NA17RJ1224).
    Keywords: Sensors ; Subtropics ; Surface observations ; Sea surface temperature
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  • 19
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 20 (2007): 4255-4266, doi:10.1175/JCLI4254.1
    Description: The Indian monsoon–El Niño–Southern Oscillation (ENSO) relationship, according to which a drier than normal monsoon season precedes peak El Niño conditions, weakened significantly during the last two decades of the twentieth century. In this work an ensemble of integrations of an atmospheric general circulation model (AGCM) coupled to an ocean model in the Indian Basin and forced with observed sea surface temperatures (SSTs) elsewhere is used to investigate the causes of such a weakening. The observed interdecadal variability of the ENSO–monsoon relationship during the period 1950–99 is realistically simulated by the model and a dominant portion of the variability is associated with changes in the tropical Atlantic SSTs in boreal summer. In correspondence to ENSO, the tropical Atlantic SSTs display negative anomalies south of the equator in the last quarter of the twentieth century and weakly positive anomalies in the previous period. Those anomalies in turn produce heating anomalies, which excite a Rossby wave response in the Indian Ocean in both the model and the reanalysis data, impacting the time-mean monsoon circulation. The proposed mechanism of remote response of the Indian rainfall to tropical Atlantic sea surface temperatures is further tested forcing the AGCM coupled to the ocean model in the Indian Basin with climatological SSTs in the Atlantic Ocean and observed anomalies elsewhere. In this second ensemble the ENSO–monsoon relationship is characterized by a stable and strong anticorrelation through the whole second half of the twentieth century.
    Description: The experiments in this paper were performed as a contribution to the ENSEMBLES project funded by the European Commission’s 6th Framework Programme, Contract GOCE-CT-2003-505539
    Keywords: ENSO ; Monsoons ; Atlantic ocean ; Regression analysis ; Sea surface temperature
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  • 20
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013]. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 26 (2013): 6775–6800, doi:10.1175/JCLI-D-12-00184.1.
    Description: Ocean carbon uptake and storage simulated by the Community Earth System Model, version 1–Biogeochemistry [CESM1(BGC)], is described and compared to observations. Fully coupled and ocean-ice configurations are examined; both capture many aspects of the spatial structure and seasonality of surface carbon fields. Nearly ubiquitous negative biases in surface alkalinity result from the prescribed carbonate dissolution profile. The modeled sea–air CO2 fluxes match observationally based estimates over much of the ocean; significant deviations appear in the Southern Ocean. Surface ocean pCO2 is biased high in the subantarctic and low in the sea ice zone. Formation of the water masses dominating anthropogenic CO2 (Cant) uptake in the Southern Hemisphere is weak in the model, leading to significant negative biases in Cant and chlorofluorocarbon (CFC) storage at intermediate depths. Column inventories of Cant appear too high, by contrast, in the North Atlantic. In spite of the positive bias, this marks an improvement over prior versions of the model, which underestimated North Atlantic uptake. The change in behavior is attributable to a new parameterization of density-driven overflows. CESM1(BGC) provides a relatively robust representation of the ocean–carbon cycle response to climate variability. Statistical metrics of modeled interannual variability in sea–air CO2 fluxes compare reasonably well to observationally based estimates. The carbon cycle response to key modes of climate variability is basically similar in the coupled and forced ocean-ice models; however, the two differ in regional detail and in the strength of teleconnections.
    Description: The CESM project is supported by the National Science Foundation and the Office of Science (BER) of the U.S. Department of Energy. SCD acknowledges support of Collaborative Research: Improved Regional and Decadal Predictions of the Carbon Cycle (NSFAGS- 1048827).
    Description: 2014-03-15
    Keywords: Carbon cycle ; Carbon dioxide ; Climate change ; Climate models ; Coupled models ; Oceanic chemistry
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  • 21
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 23 (2010): 3146–3154, doi:10.1175/2010JCLI3310.1.
    Description: 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.
    Description: We wish to acknowledge support (TJ) from WHOI’s Paul Fye Chair and NASA (NNXZX09AF35G) and to NOAA/OAR (RZ) for this work.
    Keywords: Sea surface temperature ; Meridional overturning circulation ; Gyres ; Coupled models ; Atmosphere-ocean interaction
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  • 22
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 1253-1266, doi:10.1175/2007JPO3786.1.
    Description: Wind stress and tidal dissipation are the most important sources of mechanical energy for maintaining the oceanic general circulation. The contribution of mechanical energy due to tropical cyclones can be a vitally important factor in regulating the oceanic general circulation and its variability. However, previous estimates of wind stress energy input were based on low-resolution wind stress data in which strong nonlinear events, such as tropical cyclones, were smoothed out. Using a hurricane–ocean coupled model constructed from an axisymmetric hurricane model and a three-layer ocean model, the rate of energy input to the world’s oceans induced by tropical cyclones over the period from 1984 to 2003 was estimated. The energy input is estimated as follows: 1.62 TW to the surface waves and 0.10 TW to the surface currents (including 0.03 TW to the near-inertial motions). The rate of gravitational potential energy increase due to tropical cyclones is 0.05 TW. Both the energy input from tropical cyclones and the increase of gravitational potential energy of the ocean show strong interannual and decadal variability with an increasing rate of 16% over the past 20 years. The annual mean diapycnal upwelling induced by tropical cyclones over the past 20 years is estimated as 39 Sv (Sv ≡ 106 m3 s−1). Owing to tropical cyclones, diapycnal mixing in the upper ocean (below the mixed layer) is greatly enhanced. Within the regimes of strong activity of tropical cyclones, the increase of diapycnal diffusivity is on the order of (1 − 6) × 10−4 m2 s−1. The tropical cyclone–related energy input and diapycnal mixing may play an important role in climate variability, ecology, fishery, and environments.
    Description: LLL and WW were supported by the National Basic Research Priorities Programmer of China through Grant 2007CB816004 and National Outstanding Youth Natural Science Foundation of China FIG. 15. Annual-mean vertical diffusivity induced by tropical cyclones from 1984 to 2003 (units: 10 4 m2 s 1): (right) the horizontal distribution and (left) the zonally averaged vertical diffusivity. JUNE 2008 L IU ET AL . 1265 under Grant 40725017. RXH was supported by the W. Alan Clark Chair from Woods Hole Oceanographic Institution.
    Keywords: Tropical cyclones ; Ocean circulation ; Wind stress ; Mixing ; Interannual variability
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  • 23
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 753-770, doi:10.1175/2007JPO3808.1.
    Description: A tidally and cross-sectionally averaged model based on the temporal evolution of the quasi-steady Hansen and Rattray equations is applied to simulate the salinity distribution and vertical exchange flow along the Hudson River estuary. The model achieves high skill at hindcasting salinity and residual velocity variation during a 110-day period in 2004 covering a wide range of river discharges and tidal forcing. The approach is based on an existing model framework that has been modified to improve model skill relative to observations. The external forcing has been modified to capture meteorological time-scale variability in salinity, stratification, and residual velocity due to sea level fluctuations at the open boundary and along-estuary wind stress. To reflect changes in vertical mixing due to stratification, the vertical mixing coefficients have been modified to use the bottom boundary layer height rather than the water depth as an effective mixing length scale. The boundary layer parameterization depends on the tidal amplitude and the local baroclinic pressure gradient through the longitudinal Richardson number, and improves the model response to spring–neap variability in tidal amplitude during periods of high river discharge. Finally, steady-state model solutions are evaluated for both the Hudson River and northern San Francisco Bay over a range of forcing conditions. Agreement between the model and scaling of equilibrium salinity intrusions lends confidence that the approach is transferable to other estuaries, despite significant differences in bathymetry. Discrepancies between the model results and observations at high river discharge are indicative of limits at which the formulation begins to fail, and where an alternative approach that captures two-layer dynamics would be more appropriate.
    Description: This research was supported by the Hudson River Foundation Grant 005/03A, NSF Grant OCE-0452054, and by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the J. Seward Johnson Fund.
    Keywords: Estuaries ; Salinity ; Rivers ; Tides ; Wind stress
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  • 24
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 2145–2163, doi:10.1175/2008JPO3961.1.
    Description: This is the first of a two-part investigation of a coupled wind and wave model that includes the enhanced form drag of breaking waves. In Part I here the model is developed and applied to mature seas. Part II explores the solutions in a wide range of wind and wave conditions, including growing seas. Breaking and nonbreaking waves induce air-side fluxes of momentum and energy above the air–sea interface. By balancing air-side momentum and energy and by conserving wave energy, coupled nonlinear advance–delay differential equations are derived, which govern simultaneously the wave and wind field. The system of equations is closed by introducing a relation between the wave height spectrum and wave dissipation due to breaking. The wave dissipation is proportional to nonlinear wave interactions, if the wave curvature spectrum is below the “threshold saturation level.” Above this threshold the wave dissipation rapidly increases so that the wave height spectrum is limited. The coupled model is applied to mature wind-driven seas for which the wind forcing only occurs in the equilibrium range away from the spectral peak. Modeled wave height curvature spectra as functions of wavenumber k are consistent with observations and transition from k1/2 at low wavenumbers to k0 at high wavenumbers. Breaking waves affect only weakly the wave height spectrum. Furthermore, the wind input to waves is dominated by nonbreaking waves closer to the spectral peak. Shorter breaking waves, however, can support a significant fraction, which increases with wind speed, of the total air–sea momentum flux.
    Description: This work was supported by the U.S. National Science Foundation (Grant OCE-0526177) and the U.S. Office of Naval Research (Grant N00014-06-10729).
    Keywords: Coupled models ; Wind ; Wind waves ; Wave breaking ; Momentum
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  • 25
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 23 (2010): 4841–4855, doi:10.1175/2010JCLI3273.1.
    Description: A 1-Myr-long time-dependent solution of a zonally averaged ocean–atmosphere model subject to Milankovitch forcing is examined to gain insight into long-term changes in the planetary-scale meridional moisture flux in the atmosphere. The model components are a one-dimensional (latitudinal) atmospheric energy balance model with an active hydrological cycle and an ocean circulation model representing four basins (Atlantic, Indian, Pacific, and Southern Oceans). This study finds that the inclusion of an active hydrological cycle does not significantly modify the responses of annual-mean air and ocean temperatures to Milankovitch forcing found in previous integrations with a fixed hydrological cycle. Likewise, the meridional overturning circulation of the North Atlantic Ocean is not significantly affected by hydrological changes. Rather, it mainly responds to precessionally driven variations of ocean temperature in subsurface layers (between 70- and 500-m depth) of this basin. On the other hand, annual and zonal means of evaporation rate and meridional flux of moisture in the atmosphere respond notably to obliquity-driven changes in the meridional gradient of annual-mean insolation. Thus, when obliquity is decreased (increased), the meridional moisture flux in the atmosphere is intensified (weakened). This hydrological response is consistent with deuterium excess records from polar ice cores, which are characterized by dominant obliquity cycles.
    Description: A. A. thanks the Global Environmental and Climate Change Centre of McGill University for a Network Grant that made possible an enriching twoweek stay at WHOI during June 2007. O. M. acknowledges support from theU.S.National Science Foundation. Support from a Canadian NSERC Discovery Grant awarded to L.A.M. is gratefully acknowledged.
    Keywords: Forcing ; Moisture ; Fluxes ; Ocean models ; Coupled models ; Southern Ocean ; Pacific Ocean ; Atlantic Ocean ; Indian Ocean
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  • 26
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 22 (2009): 4066–4082, doi:10.1175/2009JCLI2629.1.
    Description: Small-scale variation in wind stress due to ocean–atmosphere interaction within the atmospheric boundary layer alters the temporal and spatial scale of Ekman pumping driving the double-gyre circulation of the ocean. A high-resolution quasigeostrophic (QG) ocean model, coupled to a dynamic atmospheric mixed layer, is used to demonstrate that, despite the small spatial scale of the Ekman-pumping anomalies, this phenomenon significantly modifies the large-scale ocean circulation. The primary effect is to decrease the strength of the nonlinear component of the gyre circulation by approximately 30%–40%. This result is due to the highest transient Ekman-pumping anomalies destabilizing the flow in a dynamically sensitive region close to the western boundary current separation. The instability of the jet produces a flux of potential vorticity between the two gyres that acts to weaken both gyres.
    Description: AH and WD were supported by an ARC Linkage International Grant (LX0668781). WD was also supported by NSF Grants OCE 0424227 and OCE 0550139. Funding for PB was provided by NSF Grants OCE 0344094 and OCE 0725796 and by the research grant from the Newton Trust of the University of Cambridge. SK was supported by U.S. DOE Grant DE-FG02–02ER63413 and NASA Grant NNG-06- AG66G-1.
    Keywords: Airndashsea interaction ; Coupled models ; Mesoscale processes ; Wind stress ; Ekman pumping/transport
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  • 27
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 39 (2009): 2685-2710, doi:10.1175/2009JPO3980.1.
    Description: The aqueous thermal boundary layer near to the ocean surface, or skin layer, has thickness O(1 mm) and plays an important role in controlling the exchange of heat between the atmosphere and the ocean. Theoretical arguments and experimental measurements are used to investigate the dynamics of the skin layer under the influence of an upwelling flow, which is imposed in addition to free convection below a cooled water surface. Previous theories of straining flow in the skin layer are considered and a simple extension of a surface straining model is posed to describe the combination of turbulence and an upwelling flow. An additional theory is also proposed, conceptually based on the buoyancy-driven instability of a laminar straining flow cooled from above. In all three theories considered two distinct regimes are observed for different values of the Péclet number, which characterizes the ratio of advection to diffusion within the skin layer. For large Péclet numbers, the upwelling flow dominates and increases the free surface temperature, or skin temperature, to follow the scaling expected for a laminar straining flow. For small Péclet numbers, it is shown that any flow that is steady or varies over long time scales produces only a small change in skin temperature by direct straining of the skin layer. Experimental measurements demonstrate that a strong upwelling flow increases the skin temperature and suggest that the mean change in skin temperature with Péclet number is consistent with the theoretical trends for large Péclet number flow. However, all of the models considered consistently underpredict the measured skin temperature, both with and without an upwelling flow, possibly a result of surfactant effects not included in the models.
    Description: The work was initiated during the Woods Hole Oceanographic Institution Geophysical Fluid Dynamics Program, where AJW was supported by a fellowship of the program. CC was supported by NSF Grant OCE-82633900. JTF was supported in part by The Penzance Endowed Fund in Support of Assistant Scientists. CJZ was supported by NSF Grant OCE-0425395 and the Office of Naval Research Young Investigator Program Grant N00014-04-1-0621. Additional funding for this research came from the U.S. Office of Naval Research through the Coupled Boundary Layer Air-Sea Transfer Departmental Research Initiative (Grants N00014-05-10090 and N00014-05-1-0036).
    Keywords: Sea/ocean surface ; Sea surface temperature ; Surface layer ; Heat budgets ; Model comparison
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  • 28
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 26 (2013): 9247–9290, doi:10.1175/JCLI-D-12-00593.1.
    Description: This is the second part of a three-part paper on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) that evaluates the twentieth-century simulations of intraseasonal to multidecadal variability and teleconnections with North American climate. Overall, the multimodel ensemble does reasonably well at reproducing observed variability in several aspects, but it does less well at capturing observed teleconnections, with implications for future projections examined in part three of this paper. In terms of intraseasonal variability, almost half of the models examined can reproduce observed variability in the eastern Pacific and most models capture the midsummer drought over Central America. The multimodel mean replicates the density of traveling tropical synoptic-scale disturbances but with large spread among the models. On the other hand, the coarse resolution of the models means that tropical cyclone frequencies are underpredicted in the Atlantic and eastern North Pacific. The frequency and mean amplitude of ENSO are generally well reproduced, although teleconnections with North American climate are widely varying among models and only a few models can reproduce the east and central Pacific types of ENSO and connections with U.S. winter temperatures. The models capture the spatial pattern of Pacific decadal oscillation (PDO) variability and its influence on continental temperature and West Coast precipitation but less well for the wintertime precipitation. The spatial representation of the Atlantic multidecadal oscillation (AMO) is reasonable, but the magnitude of SST anomalies and teleconnections are poorly reproduced. Multidecadal trends such as the warming hole over the central–southeastern United States and precipitation increases are not replicated by the models, suggesting that observed changes are linked to natural variability.
    Description: The authors acknowledge the support of NOAA/Climate Program Office/Modeling, Analysis, Predictions and Projections (MAPP) program as part of the CMIP5 Task Force.
    Description: 2014-06-01
    Keywords: North America ; Regional effects ; Coupled models ; Decadal variability ; Interannual variability ; Intraseasonal variability
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  • 29
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 23 (2010): 6221–6233, doi:10.1175/2010JCLI3402.1.
    Description: Enhanced decadal variability in sea surface temperature (SST) centered on the Kuroshio Extension (KE) has been found in the Community Climate System Model version 3 (CCSM3) as well as in other coupled climate models. This decadal peak has higher energy than is found in nature, almost twice as large in some cases. While previous analyses have concentrated on the mechanisms for such decadal variability in coupled models, an analysis of the causes of excessive SST response to changes in wind stress has been missing. Here, a detailed comparison of the relationships between interannual changes in SST and sea surface height (SSH) as a proxy for geostrophic surface currents in the region in both CCSM3 and observations, and how these relationships depend on the mean ocean circulation, temperature, and salinity, is made. We use observationally based climatological temperature and salinity fields as well as satellite-based SSH and SST fields for comparison. The primary cause for the excessive SST variability is the coincidence of the mean KE with the region of largest SST gradients in the model. In observations, these two regions are separated by almost 500 km. In addition, the too shallow surface oceanic mixed layer in March north of the KE in the subarctic Pacific contributes to the biases. These biases are not unique to CCSM3 and suggest that mean biases in current, temperature, and salinity structures in separated western boundary current regions can exert a large influence on the size of modeled decadal SST variability.
    Description: Support for L.T. was provided by the NASA sponsored Ocean Surface Topography Science Team, under Contract 1267196 with the University of Washington, administered by the Jet Propulsion Laboratory. Support for Y.-O. K. comes from the NOAA Office of Global Programs (grant to C. Deser and Y.-O. Kwon) and the WHOI Heyman fellowship.
    Keywords: Bias ; Coupled models ; Decadal variability ; Ocean models ; Sea surface temperature ; Wind stress
    Repository Name: Woods Hole Open Access Server
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  • 30
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 1940–1958, doi:10.1175/JPO-D-13-020.1.
    Description: The spatial structure of the tidal and background circulation over the inner shelf south of Martha's Vineyard, Massachusetts, was investigated using observations from a high-resolution, high-frequency coastal radar system, paired with satellite SSTs and in situ ADCP velocities. Maximum tidal velocities for the dominant semidiurnal constituent increased from 5 to 35 cm s−1 over the 20-km-wide domain with phase variations up to 60°. A northeastward jet along the eastern edge and a recirculation region inshore dominated the annually averaged surface currents, along with a separate along-shelf jet offshore. Owing in part to this variable circulation, the spatial structure of seasonal SST anomalies had implications for the local heat balance. Cooling owing to the advective heat flux divergence was large enough to offset more than half of the seasonal heat gain owing to surface heat flux. Tidal stresses were the largest terms in the mean along- and across-shelf momentum equations in the area of the recirculation, with residual wind stress and the Coriolis term dominating to the west and south, respectively. The recirculation was strongest in summer, with mean winds and tidal stresses accounting for much of the differences between summer and winter mean circulation. Despite the complex bathymetry and short along-shelf spatial scales, a simple model of tidal rectification was able to recreate the features of the northeastward jet and match an estimate of the across-shelf structure of sea surface height inferred from the residual of the momentum analysis.
    Description: 2014-03-01
    Keywords: Coastal flows ; Momentum ; Sea surface temperature ; Tides ; Surface observations
    Repository Name: Woods Hole Open Access Server
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  • 31
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 23 (2010): 3249-3281, doi:10.1175/2010JCLI3343.1.
    Description: Ocean–atmosphere interaction over the Northern Hemisphere western boundary current (WBC) regions (i.e., the Gulf Stream, Kuroshio, Oyashio, and their extensions) is reviewed with an emphasis on their role in basin-scale climate variability. SST anomalies exhibit considerable variance on interannual to decadal time scales in these regions. Low-frequency SST variability is primarily driven by basin-scale wind stress curl variability via the oceanic Rossby wave adjustment of the gyre-scale circulation that modulates the latitude and strength of the WBC-related oceanic fronts. Rectification of the variability by mesoscale eddies, reemergence of the anomalies from the preceding winter, and tropical remote forcing also play important roles in driving and maintaining the low-frequency variability in these regions. In the Gulf Stream region, interaction with the deep western boundary current also likely influences the low-frequency variability. Surface heat fluxes damp the low-frequency SST anomalies over the WBC regions; thus, heat fluxes originate with heat anomalies in the ocean and have the potential to drive the overlying atmospheric circulation. While recent observational studies demonstrate a local atmospheric boundary layer response to WBC changes, the latter’s influence on the large-scale atmospheric circulation is still unclear. Nevertheless, heat and moisture fluxes from the WBCs into the atmosphere influence the mean state of the atmospheric circulation, including anchoring the latitude of the storm tracks to the WBCs. Furthermore, many climate models suggest that the large-scale atmospheric response to SST anomalies driven by ocean dynamics in WBC regions can be important in generating decadal climate variability. As a step toward bridging climate model results and observations, the degree of realism of the WBC in current climate model simulations is assessed. Finally, outstanding issues concerning ocean–atmosphere interaction in WBC regions and its impact on climate variability are discussed.
    Description: Funding for LT was provided by the NASA-sponsored Ocean Surface Topography Science Team, under Contract 1267196 with the University of Washington, administered by the Jet Propulsion Laboratory. HN was supported in part by the Grant-in-Aid 18204044 by the Japan Society for Promotion for Science (JSPS) and the Global Environment Research Fund (S-5) of the Japanese Ministry of Environment. YK was supported by the Kerr Endowed Fund and Penzance Endowed Fund.
    Keywords: Currents ; Sea surface temperature ; Anomalies ; Large-scale motions ; Oceanic mixed layer ; Northern Hemisphere
    Repository Name: Woods Hole Open Access Server
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  • 32
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 24 (2011): 2429–2449, doi:10.1175/2010JCLI3997.1.
    Description: Continuous estimates of the oceanic meridional heat transport in the Atlantic are derived from the Rapid Climate Change–Meridional Overturning Circulation (MOC) and Heatflux Array (RAPID–MOCHA) observing system deployed along 26.5°N, for the period from April 2004 to October 2007. The basinwide meridional heat transport (MHT) is derived by combining temperature transports (relative to a common reference) from 1) the Gulf Stream in the Straits of Florida; 2) the western boundary region offshore of Abaco, Bahamas; 3) the Ekman layer [derived from Quick Scatterometer (QuikSCAT) wind stresses]; and 4) the interior ocean monitored by “endpoint” dynamic height moorings. The interior eddy heat transport arising from spatial covariance of the velocity and temperature fields is estimated independently from repeat hydrographic and expendable bathythermograph (XBT) sections and can also be approximated by the array. The results for the 3.5 yr of data thus far available show a mean MHT of 1.33 ± 0.40 PW for 10-day-averaged estimates, on which time scale a basinwide mass balance can be reasonably assumed. The associated MOC strength and variability is 18.5 ± 4.9 Sv (1 Sv ≡ 106 m3 s−1). The continuous heat transport estimates range from a minimum of 0.2 to a maximum of 2.5 PW, with approximately half of the variance caused by Ekman transport changes and half caused by changes in the geostrophic circulation. The data suggest a seasonal cycle of the MHT with a maximum in summer (July–September) and minimum in late winter (March–April), with an annual range of 0.6 PW. A breakdown of the MHT into “overturning” and “gyre” components shows that the overturning component carries 88% of the total heat transport. The overall uncertainty of the annual mean MHT for the 3.5-yr record is 0.14 PW or about 10% of the mean value.
    Description: This research was supported by the U.S. National Science Foundation under Awards OCE0241438 and OCE0728108, by the U.K. RAPID Programme (RAPID Grant NER/T/S/2002/00481), and by the U.S. National Oceanic and Atmospheric Administration, as part of its Western Boundary Time Series Program.
    Keywords: Atlantic Ocean ; Meridonial overturning circulation ; Sea surface temperature ; Transport ; Anomalies
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  • 33
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 7781–7801, doi:10.1175/JCLI-D-11-00442.1.
    Description: Air–sea fluxes from the Community Climate System Model version 4 (CCSM4) are compared with the Coordinated Ocean-Ice Reference Experiment (CORE) dataset to assess present-day mean biases, variability errors, and late twentieth-century trend differences. CCSM4 is improved over the previous version, CCSM3, in both air–sea heat and freshwater fluxes in some regions; however, a large increase in net shortwave radiation into the ocean may contribute to an enhanced hydrological cycle. The authors provide a new baseline for assessment of flux variance at annual and interannual frequency bands in future model versions and contribute a new metric for assessing the coupling between the atmospheric and oceanic planetary boundary layer (PBL) schemes of any climate model. Maps of the ratio of CCSM4 variance to CORE reveal that variance on annual time scales has larger error than on interannual time scales and that different processes cause errors in mean, annual, and interannual frequency bands. Air temperature and specific humidity in the CCSM4 atmospheric boundary layer (ABL) follow the sea surface conditions much more closely than is found in CORE. Sensible and latent heat fluxes are less of a negative feedback to sea surface temperature warming in the CCSM4 than in the CORE data with the model’s PBL allowing for more heating of the ocean’s surface.
    Description: The CESM project is supported by the National Science Foundation and the Office of Science (BER) of the U.S. Department of Energy. S. Stevensonwas supported byNASAGrantNNX09A020H and B. Fox-Kemper by Grants NSF 0934737 and NASA NNX09AF38G.
    Description: 2013-05-15
    Keywords: Atmosphere-ocean interaction ; Boundary layer ; Sea surface temperature ; Climate models ; Coupled models ; Model evaluation/performance
    Repository Name: Woods Hole Open Access Server
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