Arbic, B. K., R. B. Scott, G. R. Flierl, A. J. Morten, J. G. Richman, and J. F. Shriver, Nonlinear cascades of surface oceanic geostrophic energy in the frequency domain, J. Phys. Oceanography, (in press), 2012, #2471
Scott, R. B., and D. Furnival, Assessment of traditional and new eigenfuncion bases applied to extrapolation of surface geostrophic current time series below the surface in an idealized primitive equation simulation, J. Phys. Oceanography, 42, 165-178, 2012, doi:10.1175/2011JPO4523.1, #2396 
Three strategies were compared for extrapolating surface geostrophic velocities to below the surface: S1, using only the barotropic or first baroclinic mode; S2, using a fixed or 'phase locked' linear combination of the first baroclinic mode and the barotropic mode; and S3, a strategy similar to S2 but using a new set of basis functions. For S2 and S3, the phase locking allows one to impose zero velocity at the seafloor. The new basis functions start from zero at the surface, are not degenerate with respect to the free-surface boundary condition, and represent the adjustment of the pressure at a given depth from density surfaces responding to sea surface height undulations. In idealized primitive equation simulations, strategy S3 had the least error and allowed extrapolation to deeper levels, suggesting the new basis functions performed significantly better than the traditional baroclinic modes. In contrast, strategies S1 and S2 made poor predictions by 400-m depth. Large temporal fluctuations in the fraction of energy in the barotropic and first baroclinic modes could explain the poor predictions by strategies S1 and S2. This brings into question the interpretation of the sea surface height gradients measured by satellite altimetry in terms of first baroclinic mode motions
Scott, R. B., N. Ferry, M. Drevillon, C. N. Barron, N. C. Jourdain, J.-M. Lellouche, E. J. Metzger, M.-H. Rio, and O. M. Smedstad, Estimates of surface drifter trajectories in the equatorial Atlantic: A multi-model ensemble approach, Ocean Dynamics, (in press), 2012, #2481
Timko, P. G., B. K. Arbic, J. G. Richman, R. B. Scott, E. J. Metzger, and A. J. Wallcraft, Skill tests of three-dimensional tidal currents in a global ocean model: A look at the North Atlantic, J. Geophys. Res., (in press), 2012, #2453
Wright, C., R. B. Scott, B. K. Arbic, and D. Furnival, Ocean-eddy dissipation estimates at the Atlantic zonal boundaries, J. Geophys. Res., (in press), 2012, #2452
Arbic, B. K., R. B. Scott, D. Chelton, J. G. Richman, and J. F. Shriver, Effects of stencil width on surface ocean geostrophic velocity and vorticity estimation from gridded satellite altimeter data, J. Geophys. Res., (in press), 2011, #2397
Scott, R. B., J. A. Goff, A. C. Naveira-Garaboto, and A. J. G. Nurnser, Global rate and spectral characteristics of internal gravity wave generation by geostrophic flow over topography, J. Geophys. Res., 116, C09029, 2011, doi:10.1029/2011JC007005, #2382
The rate of generation of internal gravity waves in the lee of small length scale topography by geostrophic flow in the World Ocean was estimated using linear theory with corrections for finite amplitude topography. Several global data sets were combined for the calculation including an ocean circulation model for the near-bottom geostrophic flow statistics, over 500 abyssal current meter records, historical climatological data for the buoyancy frequency, and two independent estimates of the small scale topographic statistical properties. The first topography estimate was based on an empirically-derived relationship between paleo-spreading rates and abyssal hill roughness, with corrections for sedimentation. The second estimate was based on small-scale (<100~km) roughness of satellite altimetry-derived gravity field, using upward continuation relationships to derive estimates of abyssal hill roughness at the seafloor at scales less than approximately 20~km. The lee wave generation rate was found to be between 0.34 to 0.49~TW. The Southern Hemisphere produced 89% of the lee wave energy, with the Southern Ocean dominating. Strength of the bottom flow was the most important factor in producing the global pattern of generation rate, except in the Indian Ocean where extremely rough topography produced strong lee wave generation despite only moderate bottom flows. The results imply about one half of the mechanical power input to the ocean general circulation from the extra-equatorial wind stress of the World Ocean results from abyssal lee wave generation. Topographic length scales between 176~m and 2.5~km (horizontal wavelengths between 1 and 16~km) accounted for 90% of the globally integrated generation.
Scott, R. B., B. K. Arbic, E. P. Chassignet, A. C. Coward, M., Maltrud, W. J. Merryfield, A. Srinivasan, and A. Varghese, Total kinetic energy in four global eddying ocean circulation models and over 5000 current meter records, Ocean Modelling, 32, 157-169, 2010, 3 citations, doi:10.1016/j.ocemod.2010.01.005, #2182
We compare the total kinetic energy (TKE) in four global eddying ocean circulation simulations with a global dataset of over 5000, quality controlled, moored current meter records. At individual mooring sites, there was considerable scatter between models and observations that was greater than estimated statistical uncertainty. Averaging over all current meter records in various depth ranges, all four models had mean TKE within a factor of two of observations above 3500 m, and within a factor of three below 3500 m. With the exception of observations between 20 and 100 m, the models tended to straddle the observations. However, individual models had clear biases. The free running (no data assimilation) model biases were largest below 2000 m. Idealized simulations revealed that the parameterized bottom boundary layer tidal currents were not likely the source of the problem, but that reducing quadratic bottom drag coefficient may improve the fit with deep observations. Data assimilation clearly improved the model-observation comparison, especially below 2000 m, despite assimilated data existing mostly above this depth and only south of 47 ðN. Different diagnostics revealed different aspects of the comparison, though in general the models appeared to be in an eddying-regime with TKE that compared reasonably well with observations.
Scott, R. B., C. L. Holland, and T. M. Quinn, Multidecadal trends in instrumental SST and coral proxy Sr/Ca records, J. Climate, 23, 1017-1033, 2010, doi:10.1175/2009JCLI2386.1, #2202
Historical ship observations of sea surface temperature (SST) from 1850 to present were used to compute linear 40-yr trends for all 5° latitude by 5° longitude grid cells with sufficient data. Trends from throughout the twentieth century were centered about a 7 mK yrâ1 warming trend with standard deviation 14 mK yrâ1. Although different with high statistical significance from a distribution with zero mean, the warming trends were not unusual in amplitude compared to the available nineteenth-century trends. Trends at the same grid points from the latter half of the nineteenth century were distributed about near-zero mean with standard deviation 17 mK yrâ1. The shift in mean is robust to accounting for the biases arising from differing observational methods prior to 1942. The 40-yr trends from the latter half of the twentieth century were centered about 10 ± 4 mK yrâ1 and more clearly distinct from earlier trends. Linear 40-yr trends were computed at different locations and times from all publicly available coral skeleton records of the concentration ratio of Sr to Ca. The pre-twentieth-century distribution of 40-yr trends in the Sr/Ca ratio was significantly different from the twentieth-century trends, consistent with the warming found in the instrumental SST. The interpretation of the coral Sr/Ca 40-yr trends cannot yet be reduced to a single factor. Major uncertainties were due to (i) the correlation of modern Sr/Ca records with instrumental SST being dominated by seasonal effects, with correlations on time scales longer than the annual cycle much lower, and (ii) the poor quality instrumental SST on long time scales in remote locations. Based on the NOAA extended reconstructed instrumental SST dataset since 1870 and 499 yr of Sr/Ca data from 13 different coral records, the authors found a Pearson correlation coefficient r = â0.77 for 40-yr low-pass-filtered times series. Interpreting the change in distribution of trends in Sr/Ca will require further study of the factors affecting Sr/Ca on time scales longer than seasonal.
Scott, R. B., M. Bourassa, D. Chelton, P. Cipollini, R. Ferrari, L. L. Fu, B. Galperin, S. Gille, H.-P. Huang, P. Klein, M. Maximenko, R. Morrow, B. Qiu, E. Rodriguez, D. Stammer, R. Tailleux, and C. Wuench, Integrating satellite altimetry and key observations: What we've learned, and what's possible with new technologies, in OceanOBS 09: Sustained Ocean Observations and Information for Society, edited by J. Hall, D. E. Harrison, and D. Stammer, Proc. vol. 2., ESA Publicaiton WPP-306, 2010, #2207
Arbic, B. K., J. F. Shriver, P. J. Hogan, H. E. Hurlburt, J. L. McClean, E. J. Metzger, R. B. Scott, A. Sen, O. M. Smedstad, and A. J. Wallcraft, Estimates of bottom flows and bottom boundary layer dissipation of the oceanic general circulation from global high-resolution models, J. Geophys. Res., 114, C02024, 2009, 8 citations, doi:10.1029/2008JC005072, #2059
This paper (1) compares the bottom flows of three existing high-resolution global simulations of the oceanic general circulation to near-bottom flows in a current meter database and (2) estimates, from the simulations, the global energy dissipation rate of the general circulation by quadratic bottom boundary layer drag. The study utilizes a data-assimilative run of the Naval Research Laboratory Layered Ocean Model (NLOM), a nonassimilative run of NLOM, and a nonassimilative run of the Parallel Ocean Program z-level ocean model. Generally speaking, the simulations have some difficulty matching the flows in individual current meter records. However, averages of model values of (the time average of the cube of bottom velocity, which is proportional to the dissipation rate) computed over all the current meter sites agree to within a factor of 2.7 or better with averages computed from the current meters, at least in certain depth ranges. The models therefore likely provide reasonable order-of-magnitude estimates of areally integrated dissipation by bottom drag. Global dissipation rates range from 0.14 to 0.65 TW, suggesting that bottom drag represents a substantial sink of the ∼1 TW wind-power transformed into geostrophic motions.
Scott, R. B., and Y. S. Xu, An update on the wind power to the surface geostrophic flow, Deep-Sea Res., 56, 295-304, 2009, 6 citations, doi:10.1016/j.dsr.2008.09.010, #2032
Arbic, B. K., and R. B. Scott, On quadratic bottom drag, geostrophic turbulence, and oceanic mesoscale eddies, J. Phys. Oceanography, 38, 84-103, 2008, 10 citations, doi:10.1175/2007JPO3653.1, #1879
Many investigators have idealized the oceanic mesoscale eddy field with numerical simulations of geostrophic turbulence forced by a horizontally homogeneous, baroclinically unstable mean flow. To date such studies have employed linear bottom Ekman friction (hereinafter, linear drag). This paper presents simulations of two-layer baroclinically unstable geostrophic turbulence damped by quadratic bottom drag, which is generally thought to be more realistic. The goals of the paper are 1) to describe the behavior of quadratically damped turbulence as drag strength changes, using previously reported behaviors of linearly damped turbulence as a point of comparison, and 2) to compare the eddy energies, baroclinicities, and horizontal scales in both quadratic and linear drag simulations with observations and to discuss the constraints these comparisons place on the form and strength of bottom drag in the ocean. In both quadratic and linear drag simulations, large barotropic eddies develop with weak damping, large equivalent barotropic eddies develop with strong damping, and the comparison in goal 2 above is closest when the nondimensional friction strength parameter is of order 1. Typical values of the quadratic drag coefficient (cd ∼ 0.0025) and of boundary layer depths (Hb ∼ 50 m) imply that the quadratic friction strength parameter cdLd/Hb, where Ld is the deformation radius, may indeed be of order 1 in the ocean. Model eddies are realistic over a wider range of friction strengths when drag is quadratic, because of a reduced sensitivity to friction strength in that case. The quadratic parameter is independent of the mean shear, in contrast to the linear parameter. Plots of eddy length scales, computed from satellite altimeter data, versus mean shear and versus rough estimates of the friction strength parameters suggest that both linear and quadratic bottom drag may be active in the ocean. Topographic wave drag contains terms that are linear in the bottom flow, thus providing some justification for the use of linear bottom drag in models.
Qiu, B., R. B. Scott, and S. Chen, Length scales of eddy generation and nonlinear evolution of the seasonally modulated South Pacific subtropical countercurrent, J. Phys. Oceanography, 38, 1515-1528, 2008, 7 citations, doi:10.1175/2007JPO3856.1, #1948
The dynamical processes behind the seasonal modulation of the two-dimensional eddy kinetic energy (EKE) wavenumber spectrum in the Subtropical Countercurrent region of the South Pacific are investigated with 14 yr of satellite altimeter data and climatological hydrographic data. The authors find a seasonally modulated generation of EKE via baroclinic instability in modes with larger meridional length scales. Subsequent nonlinear eddyâeddy interactions redistribute the EKE to larger total horizontal length scales, and larger zonal scales in particular. This is confirmed by diagnosing the spectral transfer of EKE in the surface geostrophic flow, which is found to drive an anisotropic inverse cascade, being redirected in the sense consistent with the β effect, as predicted by geostrophic turbulence theory on the β plane. Because of the seasonal renewal of meridionally elongated anomalies by baroclinic instability and possibly because of the barotropization process, however, the net outcome for the formation of surface zonal flows is observed to be limited.
Scott, R. B., B. K. Arbic, C. L. Holland, A. Sen, and B. Qiu, Zonal versus meridional velocity variance in satellite observations and realistic and idealized ocean circulation models, Ocean Modelling, 23, 102-112, 2008, 8 citations, doi:10.1016/j.ocemod.2008.04.009, #1981
Global, high-quality, satellite-based observation of oceanic currents over the past 13 years has revealed ubiquitous quasi-horizontal eddies in the mesoscale (tens to hundreds of kilometers), confirming the view of a highly turbulent ocean suggested by observational programs in the 1970s. Idealized quasigeostrophic turbulence models suggest mesoscale turbulent flow can vary between isotropic, and highly anisotropic zonal jets. Here we compare the zonal and meridional velocity variance from satellite altimetry. We find that, for an unexplained reason and despite the chaotic nature of turbulence, the surface flow is organized into mesoscale patches where either zonal or meridional velocity variance dominates. The patches persist over 13 years, much longer than the turbulent timescale of a few months. Implications include potentially highly anisotropic redistribution of tracers by the mesoscale flow. Zonally averaged velocity variances reveal a slight preference for meridional over zonal velocity variance. Realistic primitive equation models succeed in reproducing both the patchy structure in local preference for either zonal or meridional velocity variance, and the zonally averaged preference for meridional variance. Idealized models of fully developed, quasigeostrophic turbulence fail in both regards.
Sen, A., R. B. Scott, and B. K. Arbic, Global energy dissipation rate of deep-ocean low-frequency flows by quadratic bottom boundary layer drag: Computations from current-meter data, Geophys. Res. Lett., 35, L09606, 2008, 12 citations, doi:10.1029/2008GL033407, #2016
The global energy dissipation rate of deep-ocean low-frequency flows by quadratic bottom boundary layer drag is estimated in three ways. First, an average over the dissipations computed from the near-bottom velocities recorded by 290 moored current meters is multiplied by the World Ocean area. Second, near-global maps of surface velocities derived from satellite altimetry data are used to estimate the bias due to the sparse spatial coverage of the moorings. Third, a relationship between bottom and surface flows, computed over the mooring locations, is used to estimate global maps of bottom flows from the surface data. All three methods suggest that at least 0.2 TW of the wind-power input into geostrophic flows is dissipated in deep water by quadratic bottom drag. Implications for the oceanic overturning circulation, and for oceanic mesoscale eddy dynamics, are briefly discussed.
Xu, Y. S., and R. B. Scott, Subtleties in forcing eddy resolving ocean models with satellite wind data, Ocean Modelling, 20, 240-251, 2008, 9 citations, doi:10.1016/j.ocemod.2007.09.003, #1949
Using new global satellite remote sensing data, we show that ignoring the ocean current dependence in the wind stress artificially increases global wind power input to the oceanic general circulation by about 32%, and more than doubles the input in the regions of strong ocean current systems. Scatterometer-derived wind stress naturally accounts for the moving ocean that is not included in traditional wind stress products. However, forcing an ocean model with a scatterometer-derived wind stress cannot actually account for the ocean current effect on the wind power input. The difference between the real and modeled surface eddy fields can reduce the damping associated with the ocean current dependence in wind stress, leading to a positive bias in global wind power input of about 23%. Most of this spurious energy flux goes directly to the fluctuation eddy field and is several times larger than the energy flux to real ocean eddies.
Arbic, B. K., G. R. Flierl, and R. B. Scott, Cascade inequalities for forced-dissipative geostrophic turbulence, J. Phys. Oceanography, 37, 1470-1487, 2007, 7 citations, doi:10.1175/JPO3067.1, #1863
Analysis of spectral kinetic energy fluxes in satellite altimetry data has demonstrated that an inverse cascade of kinetic energy is ubiquitous in the ocean. In geostrophic turbulence models, a fully developed inverse cascade results in barotropic eddies with large horizontal scales. However, midocean eddies contain substantial energy in the baroclinic mode and in compact horizontal scales (scales comparable to the deformation radius Ld). This paper examines the possibility that relatively strong bottom friction prevents the oceanic cascade from becoming fully developed. The importance of the vertical structure of friction is demonstrated by contrasting numerical simulations of two-layer quasigeostrophic turbulence forced by a baroclinically unstable mean flow and damped by bottom Ekman friction with turbulence damped by vertically symmetric Ekman friction (equal decay rates in the two layers). âCascade inequalitiesâ derived from the energy and enstrophy equations are used to interpret the numerical results. In the symmetric system, the inequality formally requires a cascade to large-scale barotropic flow, independent of the stratification. The inequality is less strict when friction is in the bottom layer only, especially when stratification is surface intensified. Accordingly, model runs with surface-intensified stratification and relatively strong bottom friction retain substantial small-scale baroclinic energy. Altimetric data show that the symmetric inequality is violated in the low- and midlatitude ocean, again suggesting the potential impact of the âbottomnessâ of friction on eddies. Inequalities developed for multilayer turbulence suggest that high baroclinic modes in the mean shear also enhance small-scale baroclinic eddy energy. The inequalities motivate a new interpretation of barotropization in weakly damped turbulence. In that limit the barotropic mode dominates the spatial average of kinetic energy density because large values of barotropic density are found throughout the model domain, consistent with the barotropic cascade to large horizontal scales, while baroclinic density is spatially localized.
Holland, C. L., R. B. Scott, S.-I. An, and F. W. Taylor, Propagating decadal sea surface temperature signal identified in modern proxy records of the tropical Pacific, Climate Dynamics, 28, 163-179, 2007, 4 citations, doi:10.1007/s00382-006-0174-0, #1830
Analysis of 86 years of multiple modern coral δ18O records in the tropical Pacific reveals a basin-scale decadal pattern of variability. Although coral δ18O records the effects of both temperature and seawater δ18O variability due to salinity effects, in practice, most of the records used here agree well with observations of sea surface temperature on longer timescales. These coral proxy records reveal strong variability near a 12-year period. Their relative phasing suggests a signal propagating from the southwestern subtropical Pacific to other regions. The results are consistent with recent studies based on instrumental data and with coupled climate model studies, in which advection of thermal anomalies leads to El Niño/Southern Oscillation-like variability on decadal timescales. Additionally, there is evidence for a significant shift in many of the time series, along with a decrease in the decadal variability, occurring in the early 1940s. Finally, the proxy records indicate the presence of strong teleconnections between the eastern tropical Pacific and high latitude climate.
Merryfield, W. J., and R. B. Scott, Bathymetric influence on mean currents in two high-resolution near-global ocean models, Ocean Modelling, 16, 76-94, 2007, 14 citations, doi:10.1016/j.ocemod.2006.07.005, #1864
The question of whether mean flow generation by eddies interacting with sloping bathymetry significantly influences World Ocean circulation is approached by examining output from two near-global circulation models, OFES and the LANL/NPS POP model, having 1/10° lateral resolution. In each of these vigorously eddying models, the mean currents over sloping bathymetry tend preferentially to align with the direction of topographic Rossby wave propagation, in accordance with theories of eddy-topographic interaction. This tendency, which is particularly strong near the ocean bottom and at abyssal depths, prevails both globally and within a variety of circulation regimes including the subpolar and subtropical gyres and the extra-equatorial tropics. By contrast, two coarser (1â2°), non-eddying models exhibit flow alignments throughout much of the abyssal ocean that are oppositely directed. This result suggests that eddies play an essential role in determining the direction of mean circulation over slopes, and that non-eddying models could benefit from a parameterization of this effect.
Scott, R. B., and B. K. Arbic, Spectral energy fluxes in geostrophic turbulence: Implications for ocean energetics, J. Phys. Oceanography, 37, 673-688, 2007, 13 citations, doi:10.1175/JPO3027.1, #1859
The energy pathways in geostrophic turbulence are explored using a two-layer, flat-bottom, f-plane, quasigeostrophic model forced by an imposed, horizontally homogenous, baroclinically unstable mean flow and damped by bottom Ekman friction. A systematic presentation of the spectral energy fluxes, the mean flow forcing, and dissipation terms allows for a comprehensive understanding of the sources and sinks for baroclinic and barotropic energy as a function of length scale. The key new result is a robust inverse cascade of kinetic energy for both the baroclinic mode and the upper layer. This is consistent with recent observations of satellite altimeter data over the South Pacific Ocean. The well-known forward cascade of baroclinic potential and total energy was found to be very robust. Decomposing the spectral fluxes into contributions from different terms provided further insight. The inverse baroclinic kinetic energy cascade is driven mostly by an efficient interaction between the baroclinic velocity and the barotropic vorticity, the latter playing a crucial catalytic role. This cascade can be further enhanced by the baroclinic mode self-interaction, which is only present with nonuniform stratification (unequal layer depths). When model parameters are set such that modeled eddies compare favorably with observations, the inverse baroclinic kinetic energy cascade is actually much stronger than the well-known inverse cascade in the barotropic mode. The upper-layer kinetic energy cascade was found to dominate the lower-layer cascade over a wide range of parameters, suggesting that the surface cascade and time mean density stratification may be sufficient for estimating the depth-integrated cascade from ocean observations. This may find useful application in inferring the kinetic to gravitational potential energy conversion rate from satellite measurements.
Scott, R. B., and F. Wang, Direct evidence of an oceanic inverse kinetic energy cascade from satellite altimetry, J. Phys. Oceanography, 35, 1650-1666, 2005, 50 citations, doi:10.1175/JPO2771.1, #1792
Sea surface height measurements from satellites reveal the turbulent properties of the South Pacific Ocean surface geostrophic circulation, both supporting and challenging different aspects of geostrophic turbulence theory. A near-universal shape of the spectral kinetic energy flux is found and provides direct evidence of a source of kinetic energy near to or smaller than the deformation radius, consistent with linear instability theory. The spectral kinetic energy flux also reveals a net inverse cascade (i.e., a cascade to larger spatial scale), consistent with two-dimensional turbulence phenomenology. However, stratified geostrophic turbulence theory predicts an inverse cascade for the barotropic mode only; energy in the large-scale baroclinic modes undergoes a direct cascade toward the first-mode deformation scale. Thus if the surface geostrophic flow is predominately the first baroclinic mode, as expected for oceanic stratification profiles, then the observed inverse cascade contradicts geostrophic turbulence theory. The latter interpretation is argued for. Furthermore, and consistent with this interpretation, the inverse cascade arrest scale does not follow the Rhines arrest scale, as one would expect for the barotropic mode. A tentative revision of theory is proposed that would resolve the conflicts; however, further observations and idealized modeling experiments are needed to confirm, or refute, the revision. It is noted that no inertial range was found for the inverse cascade range of the spectrum, implying inertial range scaling, such as the established K−5/3 slope in the spectral kinetic energy density plot, is not applicable to the surface geostrophic flow.
Wang, F., and R. B. Scott, On the prediction of linear stochastic systems with a low-order model, Tellus, 57A, 12-20, 2005, doi:10.1111/j.1600-0870.2005.00088.x, #1740
Three methods for approximating the high-dimensional stochastic system with a low-dimensional model are examined, and the prediction error and predictability of the reduced-order models are evaluated. It is shown that during reduction both the normal modes of deterministic dynamics and the spatial structures of stochastic forcing need to be taken into account. In addition to stability, which determines the asymptotic behavior, non-normality, which controls the error growth at short lead times, should also be preserved. An experiment with tropical Atlantic variability illustrates that the empirical orthogonal function and balanced truncation are superior to modal reduction in capturing the predictable dynamics.
Scott, R. B., Predictability of SST in an idealized, one-dimensional, coupled atmosphere-ocean climate model with stochastic forcing and advection, J. Climate, 16, 323-335, 2003, 10 citations, #1605
The predictability of sea surface temperature (SST) is examined through analysis of an idealized, one-dimensional, stochastically forced climate model. The influence on SST predictability of including advection by a constant mean current is investigated. A new mechanism is described whereby predictability is enhanced via a cancellation of stochastically driven noise. For a sufficiently weak advective current the predictability was found to have significant departures from red noise predictability. Bounds on the predictability in the limit of zero advecting velocity were found. The relationship between autocovariance function (or power spectrum in the frequency domain) and predictability is also examined. Perhaps surprisingly, the regions with maximum predictability were not clearly identifiable by their autocovariance function (or power spectrum).
Scott, R. B., and B. Qiu, Predictability of SST in a stochastic climate model and its application to the Kuroshio Extension region, J. Climate, 16, 312-322, 2003, 7 citations, #1607
The influence of deterministic forcing on SST predictability is investigated in a zero-dimensional, stochastic, coupled atmosphere-ocean climate model. The SST anomaly predictability time is found to be very sensitive to the properties of the deterministic forcing. Comparison of the amplitudes of the deterministic and stochastic forcing terms, for example, as determined from linear regression analysis, may give a misleading impression of their relative importance. The importance of instead comparing the time-integrated forcing terms is emphasized. The conditions under which the model exhibits preferred timescales and the conditions under which the model power spectrum approaches that of a univariate Markov process (red noise) are also determined. The idealized model results are complemented with an analysis of climate observations for the Kuroshio Extension region. Observational errors and unresolved components of the enthalpy budget limited the maximum timescale considered to about 4 yr. This analysis revealed that the advection of anomalous geostrophic currents is a minor source of SST variability and not the limiting factor in determining SST predictability in that region, at least for the timescales considered
Scott, R. B., and A. J. Willmott, Steady-state frictional geostrophic circulation in a one-layer ocean model with thermodynamics, Dynamics Atmos. Oceans, 35, 389-419, 2002, doi:10.1016/S0377-0265(02)00052-0, #1604
The governing equations are developed for a steady-state frictional geostrophic inhomogeneous 1.5-layer ocean model, with horizontal velocity field that is linearly sheared in the vertical coordinate. We show that in the adiabatic, thermally non-diffusive limit there are an infinite number of solutions for the temperature and depth fields of the subtropical gyre even with the constraint of identical mass within each temperature range. In the non-adiabatic case, a unique subtropical gyre solution exists that can exhibit a temperature front, containing an unbounded meridional gradient, in the northwest corner of the solution domain. The role of mixing of enthalpy in the western boundary layer (WBL) region was investigated by comparing the two extreme cases of no mixing and complete mixing of enthalpy in this region. Also investigated was the dependence of the meridional heat transport on the airââ¬âsea heat exchange coefficient, κ. The temperature field was found to be strongly influenced by mixing. However, both qualitatively and quantitatively, the heat transport is similar in the model with and without mixing. The heat transport attains a single local maximum at κ=κc, that lies within values that are oceanographically relevant.