Papers by vittorio canuto
Geophysical & Astrophysical Fluid Dynamics, 2005
In the framework of the eddy dynamic model developed in two previous papers (Dubovikov, M.S., Dyn... more In the framework of the eddy dynamic model developed in two previous papers (Dubovikov, M.S., Dynamical model of mesoscale eddies, Geophys. Astophys. Fluid Dyn., 2003, 97, 311-358; Canuto, V.M. and Dubovikov, M.S., Modeling mesoscale eddies, Ocean Modelling, 2004, 8, 1-30 referred as I-II), we compute the contribution of unresolved mesoscale eddies to the large-scale dynamic equations of the ocean. In isopycnal coordinates, in addition to the bolus velocity discussed in I-II, the mesoscale contribution to the large scale momentum equation is derived. Its form is quite different from the traditional down-gradient parameterization. The model solutions in isopycnal coordinates are transformed to level coordinates to parameterize the eddy contributions to the corresponding large scale density and momentum equations. In the former, the contributions due to the eddy induced velocity and to the residual density flux across mean isopycnals (so called AE-term) are derived, both contributions being shown to be of the same order. As for the large scale momentum equation, as well as in isopycnal coordinates, the eddy contribution has a form which is quite different from the down-gradient expression.
arXiv (Cornell University), Jun 28, 2011
In this paper we present a model for mixed layer (ML) mesoscale fluxes of an arbitrary tracer in ... more In this paper we present a model for mixed layer (ML) mesoscale fluxes of an arbitrary tracer in terms of the resolved fields (mean tracer and mean velocity). The treatment of an arbitrary tracer, rather than only buoyancy, is necessary since OGCMs (ocean global circulation models) time step T, S, CO2, etc and not buoyancy. The particular case of buoyancy is used to assess the model results. The paper contains three parts: derivation of the results, discussion of the results and assessment of the latter using, among others, WOCE, T/P and Drifter data. Derivation. To construct the mesoscale fluxes, we first solve the ML mesoscale dynamic equations for the velocity and tracer mesoscale fields. The goal of the derivation is to emphasize the different treatments of the non-linear terms in the adiabatic vs. diabatic ocean (deep ocean vs. mixed layer). Results. We derive analytic expressions for the following variables: a) vertical and horizontal mesoscale fluxes of an arbitrary tracer, b) mesoscale diffusivity in terms of the eddy kinetic energy, c) surface value of the latter in terms of the vertical mesoscale buoyancy flux together with a model for the z-profile of the mesoscale kinetic energy, d) tapering function T(z) in terms of the large scale variables; T(z) vanishes at the surface and tends to unity below the ML where the stream function smoothly connects with the deep ocean GM form, e) new eddy induced velocity. Thus far, tracers were described by only one eddy induced velocity (curl of the stream function); for tracers other than buoyancy, we show there is an additional bolus velocity originating not from the stream function but from the residual flux which exhibits a skew component. Assessment. The model assessment includes the following items: a) the vertical flux naturally vanishes at the ocean surface, as physically required, b) the second z-derivative of the buoyancy flux is negative, implying re-stratification, in agreement with eddy resolving simulations, c) the predicted surface eddy kinetic energy compares well with the T/P-Jason-1 altimetry data in both intensity and geographical distribution, d) the predicted z-profile of the eddy kinetic energy compares well with WOCE data, e) the model predicts both the z-profile and the surface values of the mesoscale diffusivity, f) the latter is in accord with the Global Drifter and T/P data.
The Astrophysical Journal, 1996
International Astronomical Union Colloquium, 1991
We use the latest models of turbulence to compute a new expression for the turbulent convective f... more We use the latest models of turbulence to compute a new expression for the turbulent convective flux, Fc. The new values of Fc are up to ten times larger than those given by the mixing length theory, MLT. Astrophysical considerations indicate that the new model fares better with observational data than the MLT.
Journal of Physical Oceanography, 2018
In 2011, Chelton et al. carried out a comprehensive census of mesoscales using altimetry data and... more In 2011, Chelton et al. carried out a comprehensive census of mesoscales using altimetry data and reached the following conclusions: “essentially all of the observed mesoscale features are nonlinear” and “mesoscales do not move with the mean velocity but with their own drift velocity,” which is “the most germane of all the nonlinear metrics.” Accounting for these results in a mesoscale parameterization presents conceptual and practical challenges since linear analysis is no longer usable and one needs a model of nonlinearity. A mesoscale parameterization is presented that has the following features: 1) it is based on the solutions of the nonlinear mesoscale dynamical equations, 2) it describes arbitrary tracers, 3) it includes adiabatic (A) and diabatic (D) regimes, 4) the eddy-induced velocity is the sum of a Gent and McWilliams (GM) term plus a new term representing the difference between drift and mean velocities, 5) the new term lowers the transfer of mean potential energy to me...
Icarus, 1987
The theoretical framework for modeling the primordial solar nebula is presented in which convecti... more The theoretical framework for modeling the primordial solar nebula is presented in which convection is assumed to be the sole source of turbulence that causes the nebula to evolve. We use a new model of convective turbulence that takes into account the important effects of radiative dissipation, rotation, and anisotropy of convective motions. This model is based on a closure for the nonlinear interactions that employs the growth rates of hydrodynamic instabilities, a procedure that allows one to compute turbulence coefficients for instabilities other than convection. The vertical structure equations in the thin-disk approximation are developed for this new model, and a detailed comparison and critique of previous convective models of the solar nebula are presented. Numerical results are presented in a subsequent paper.
Journal of Advances in Modeling Earth Systems, 2021
Simulations of the CMIP6 historical period 1850-2014, characterized by the emergence of anthropog... more Simulations of the CMIP6 historical period 1850-2014, characterized by the emergence of anthropogenic climate drivers like greenhouse gases, are presented for different configurations of the NASA Goddard Institute for Space Studies (GISS) Earth System ModelE2.1. The GISS-E2.1 ensembles are more sensitive to greenhouse gas forcing than their CMIP5 predecessors (GISS-E2) but warm less during recent decades due to a forcing reduction that is attributed to greater longwave opacity in the GISS-E2.1 pre-industrial simulations. This results in an atmosphere less sensitive to increases in opacity from rising greenhouse gas concentrations, demonstrating the importance of the base climatology to forcing and forced climate trends. Most model versions match observed temperature trends since 1979 from the ocean to the stratosphere. The choice of ocean model is important to the transient climate response, as found previously in CMIP5 GISS-E2: the model that more efficiently exports heat to the deep ocean shows a smaller rise in tropospheric temperature. Model sea level rise over the historical period is traced to excessive drawdown of aquifers to meet irrigation demand with a smaller contribution from thermal expansion. This shows how fully coupled models can provide indirect observational constraints upon forcing, in this case, constraining irrigation rates with observed sea level changes. The overall agreement of GISS-E2.1 with observed trends is familiar from evaluation of its predecessors, as is the conclusion that these trends are almost entirely anthropogenic in origin. Plain Language Summary Measurements show clear evidence of warming over the twentieth century and up to the present day. Our anticipation of future change comes from computer models of climate. These are based upon well-established physical principles like Newton's laws of motion and radiative transfer theory; the models are closely related to those used for weather forecasting. We can never predict the weather on a particular day, 50 years in the future, but we can calculate whether that future decade will be warmer than our present climate. Part of our confidence in such a forecast comes from testing a climate model's ability to reproduce warming and other changes measured over the past century. We use observations of atmospheric composition and the sunlight received by our planet to calculate how the model responds to their changes. The climate model of the NASA Goddard Institute for Space Studies,
Journal of Advances in Modeling Earth Systems, 2020
This paper describes the GISS-E2.1 contribution to the Coupled Model Intercomparison Project, Pha... more This paper describes the GISS-E2.1 contribution to the Coupled Model Intercomparison Project, Phase 6 (CMIP6). This model version differs from the predecessor model (GISS-E2) chiefly due to parameterization improvements to the atmospheric and ocean model components, while keeping atmospheric resolution the same. Model skill when compared to modern era climatologies is significantly higher than in previous versions. Additionally, updates in forcings have a material impact on the results. In particular, there have been specific improvements in representations of modes of variability (such as the Madden-Julian Oscillation and other modes in the Pacific) and significant improvements in the simulation of the climate of the Southern Oceans, including sea ice. The effective climate sensitivity to 2 × CO 2 is slightly higher than previously at 2.7-3.1°C (depending on version) and is a result of lower CO 2 radiative forcing and stronger positive feedbacks. Plain Language Summary This paper describes the latest iteration of the National Aeronautics and Space Administration (NASA) Goddard Institute for Space Studies (GISS) climate model, which will be used for understanding historical climate change and to make projections for the future. We compare the model output to a wide range of observations over the recent era (1979-2014) and show that there has been a significant increase in how well the model performs compared to the previous version from 2014, particularly in the Southern Ocean, though some persistent biases remain. The model has a temperature response to the increase of carbon dioxide that is slightly higher than previous versions but is well within the range expected from observational and past climate constraints.
Journal of Physical Oceanography, 2019
Recently, we presented a parameterization of an arbitrary tracer 3D mesoscale flux that describes... more Recently, we presented a parameterization of an arbitrary tracer 3D mesoscale flux that describes both diabatic and adiabatic regimes without using arbitrary tapering functions. However, we did not parameterize the mesoscale diffusivity, which is the subject of this work. A key difference between the present and previous diffusivity parameterizations is that in the latter, the two main ingredients, mesoscale drift velocity and eddy kinetic energy, were not parameterized but determined using present data, which deprives the models of predictive power. Since winds, stratification, etc., are predicted to change in the future, use of these parameterizations to study future climate scenarios becomes questionable. In this work, we parameterize drift velocity and eddy kinetic energy (vertical–horizontal components), which we first assess with data [WOCE, TOPEX/Poseidon (T/P), and North Atlantic Tracer Release Experiment (NATRE)] and then use in a coarse-resolution stand-alone ocean code un...
Ocean Modelling, 2015
We characterize the representation of the Southern Ocean water mass structure and sea ice within ... more We characterize the representation of the Southern Ocean water mass structure and sea ice within a suite of 15 global ocean-ice models run with the Coordinated Ocean-ice Reference Experiment Phase II (CORE-II) protocol. The main focus is the representation of the present (1988-2007) mode and intermediate waters, thus framing an analysis of winter and summer mixed layer depths; temperature, salinity, and potential vorticity structure; and temporal variability of sea ice distributions. We also consider the inter-annual variability over the same 20 year period. Comparisons are made between models as well as to observation-based analyses where available.
Ocean Modelling, 2007
Turbulent fluxes can be represented by a diffusivity tensor, the symmetric part of which describe... more Turbulent fluxes can be represented by a diffusivity tensor, the symmetric part of which describes ''turbulent diffusion" while the anti-symmetric part describes ''advection". Diffusion is a local process in the sense that it depends only on the local gradients of the mean fields while advection is non-local for it is represented by an integral over all length scales (all eddies) that can ''fit" from say the bottom of the physical domain to the z where the fluxes are computed. In the ocean, there are two main regimes where non-local transport is important. One regime is where storms release a sudden burst of mechanical energy to the ocean surface that is then transported downward by energetic eddies that deepen the mixed layer. Even relatively simple non-local models yield results considerably more realistic than those of local models. The second regime is deep convection (DC) caused by loss of surface buoyancy, the description of which is required for a reliable assessment of water masses formation. At present, there is no reliable model for either of these non-local regimes individually or much less a formalism capable of accounting for both regimes simultaneously. The goal of this paper is to present a formalism that provides the expressions for the non-local fluxes for momentum, heat and salinity encompassing both cases. Since the resulting number of dynamic equations involves is however large, we work out two sub-models, one when only shear must be treated non-locally (e.g., when storms release mechanical energy) and one when only buoyancy is to be treated non-locally (the DC case). We employ the Reynolds Stress formalism in which non-locality is represented by the third-order moments which in turn depend on the fourth-order moments for which we employ a new model that has been tested against LES data, aircraft data and a full PBL simulation. For the DC case, we rewrite the non-local model in terms of Plumes since thus far the only non-local model used to treat oceanic DC has been the ''plume model" of Morton, Taylor and Turner (MTT model). We show that the MTT model has two key limitations, (1) an important physical process such as the rate of entrainment cannot be determined by the model and remains an adjustable parameter and (2) MTT is purely advective and thus only applicable to the initial stages of DC but not to the whole process which is both advective and diffusive. The model we derive bypasses these limitations, is a generalization of the MTT model and is applicable to the entire development of deep convection.
Journal of the Atmospheric Sciences, 2010
The goal of this paper is to derive the equation for the turbulence dissipation rate ɛ for a shea... more The goal of this paper is to derive the equation for the turbulence dissipation rate ɛ for a shear-driven flow. In 1961, Davydov used a one-point closure model to derive the ɛ equation from first principles but the final result contained undetermined terms and thus lacked predictive power. Both in 1987 (Schiestel) and in 2001 (Rubinstein and Zhou), attempts were made to derive the ɛ equation from first principles using a two-point closure, but their methods relied on a phenomenological assumption. The standard practice has thus been to employ a heuristic form of the ɛ equation that contains three empirical ingredients: two constants, c1,ɛ and c2,ɛ, and a diffusion term Dɛ. In this work, a two-point closure is employed, yielding the following results: 1) the empirical constants get replaced by c1, c2, which are now functions of K and ɛ; 2) c1 and c2 are not independent because a general relation between the two that are valid for any K and ɛ are derived; 3) c1, c2 become constant wit...
Journal of the Atmospheric Sciences, 2003
Journal of the Atmospheric Sciences, 2002
Richardson numbers of order unity. We also show that the model yields a higher PBL height than ti... more Richardson numbers of order unity. We also show that the model yields a higher PBL height than tile previous models. (17b). The expressions for the model constants are the same as in (19) except that in level 3 model 18 = 0. In addition, the constant to needed in (A4) is set to 2/3 according to (10c) and (25a).
Journal of the Atmospheric Sciences, 2005
The standard approach to studying the planetary boundary layer (PBL) via turbulence models begins... more The standard approach to studying the planetary boundary layer (PBL) via turbulence models begins with the first-moment equations for temperature, moisture, and mean velocity. These equations entail second-order moments that are solutions of dynamic equations, which in turn entail third-order moments, and so on. How and where to terminate (close) the moments equations has not been a generally agreed upon procedure and a variety of models differ precisely in the way they terminate the sequence. This can be viewed as a bottom-up approach. In this paper, a top-down procedure is suggested, worked out, and justified, in which a new closure model is proposed for the fourth-order moments (FOMs). The key reason for this consideration is the availability of new aircraft data that provide for the first time the z profile of several FOMs. The new FOM expressions have nonzero cumulants that the model relates to the z integrals of the third-order moments (TOMs), giving rise to a nonlocal model f...
Journal of Physical Oceanography, 2001
Ocean mixing processes have traditionally been formulated using one-point turbulence closure mode... more Ocean mixing processes have traditionally been formulated using one-point turbulence closure models, specifically the Mellor and Yamada (MY) models, which were pioneered in geophysics using 1980 state-of-the-art turbulence modeling. These models have been widely applied over the years, but the underlying core physical assumptions have hardly improved since the 1980s; yet, in the meantime, turbulence modeling has made sufficient progress to allow four improvements to be made. 1) The value of Ri cr. MY-type models yield a low value for the critical Richardson number, Ri cr ϭ 0.2 (the result of linear stability is Ri cr ϭ 1/4). On the other hand, nonlinear stability analysis, laboratory measurements, direct numerical simulation, large eddy simulation, and mixed layer studies indicate that Ri cr ϳ 1. The authors show that by improving the closure for the pressure correlations, the result Ri cr ϳ 1 naturally follows. 2) Nonlocal, third-order moments (TOMs). The downgradient approximation used in all models thus far seriously underestimates the TOMs. A new expression that includes both stratification and shear is presented here for the first time. It is obtained by solving the dynamic equations for the third-order moments. 3) Rotation. The MY-type models with rotation assume that the latter does not affect turbulence, specifically, neither the pressure correlations nor the rate of dissipation of turbulent kinetic energy. Recent studies show that both quantities are affected. 4) Mixing below the mixed layer. Thus far, the momentum and heat diffusivities below the mixed layer have been treated as adjustable parameters. A new model that allows use of the same turbulence model throughout the ocean depth is proposed. A new model is presented that includes 1), 2), and 4). Rotation will be dealt with in a subsequent paper. The new model is fully algebraic and easy to use in an ocean code. The new model is used in an OGCM, and the predicted global temperature and salinity profiles are compared with those of the KPP model and Levitus data.
Journal of Geophysical Research, 2005
We use a global climate model to compare the effectiveness of many climate forcing agents for pro... more We use a global climate model to compare the effectiveness of many climate forcing agents for producing climate change. We find a substantial range in the ''efficacy'' of different forcings, where the efficacy is the global temperature response per unit forcing relative to the response to CO 2 forcing. Anthropogenic CH 4 has efficacy $110%, which increases to $145% when its indirect effects on stratospheric H 2 O and tropospheric O 3 are included, yielding an effective climate forcing of $0.8 W/m 2 for the period 1750-2000 and making CH 4 the largest anthropogenic climate forcing other than CO 2. Black carbon (BC) aerosols from biomass burning have a calculated efficacy $58%, while fossil fuel BC has an efficacy $78%. Accounting for forcing efficacies and for indirect effects via snow albedo and cloud changes, we find that fossil fuel soot, defined as BC + OC (organic carbon), has a net positive forcing while biomass burning BC + OC has a negative forcing. We show that replacement of the traditional instantaneous and adjusted forcings, Fi and Fa, with an easily computed alternative, Fs, yields a better predictor of climate change, i.e., its efficacies are closer to unity. Fs is inferred from flux and temperature changes in a fixed-ocean model run. There is remarkable congruence in the spatial distribution of climate change, normalized to the same forcing Fs, for most climate forcing agents, suggesting that the global forcing has more relevance to regional climate change than may have been anticipated. Increasing greenhouse gases intensify the Hadley circulation in our model, increasing rainfall in the Intertropical Convergence Zone (ITCZ), Eastern United States, and East Asia, while intensifying dry conditions in the subtropics including the Southwest United States, the Mediterranean region, the Middle East, and an expanding Sahel. These features survive in model simulations that use all estimated forcings for the period 1880-2000. Responses to localized forcings, such as land use change and heavy regional concentrations of BC aerosols, include more specific regional characteristics. We suggest that anthropogenic tropospheric O 3 and the BC snow albedo effect contribute substantially to rapid warming and sea ice loss in the Arctic. As a complement to a priori forcings, such as Fi, Fa, and Fs, we tabulate the a posteriori effective forcing, Fe, which is the product of the forcing and its efficacy. Fe requires calculation of the climate response and introduces greater model dependence, but once it is calculated for a given amount of a forcing agent it provides a good prediction of the response to other forcing amounts.
Journal of Advances in Modeling Earth Systems, 2014
Journal of Advances in Modeling Earth Systems, 2014
We present a description of the ModelE2 version of the Goddard Institute for Space Studies (GISS)... more We present a description of the ModelE2 version of the Goddard Institute for Space Studies (GISS) General Circulation Model (GCM) and the configurations used in the simulations performed for the Coupled Model Intercomparison Project Phase 5 (CMIP5). We use six variations related to the treatment of the atmospheric composition, the calculation of aerosol indirect effects, and ocean model component. Specifically, we test the difference between atmospheric models that have noninteractive composition, where radiatively important aerosols and ozone are prescribed from precomputed decadal averages, and interactive versions where atmospheric chemistry and aerosols are calculated given decadally varying emissions. The impact of the first aerosol indirect effect on clouds is either specified using a simple tuning, or parameterized using a cloud microphysics scheme. We also use two dynamic ocean components: the Russell and HYbrid Coordinate Ocean Model (HYCOM) which differ significantly in their basic formulations and grid. Results are presented for the climatological means over the satellite era (1980-2004) taken from transient simulations starting from the preindustrial (1850) driven by estimates of appropriate forcings over the 20th Century. Differences in base climate and variability related to the choice of ocean model are large, indicating an important structural uncertainty. The impact of interactive atmospheric composition on the climatology is relatively small except in regions such as the lower stratosphere, where ozone plays an important role, and the tropics, where aerosol changes affect the hydrological cycle and cloud cover. While key improvements over previous versions of the model are evident, these are not uniform across all metrics.
Geophysical Research Letters, 2008
Available models of Double Diffusion (DD) processes (Salt Fingers, SF and Diffusive Convection, D... more Available models of Double Diffusion (DD) processes (Salt Fingers, SF and Diffusive Convection, DC) are primarily based on laboratory experiments that do not include turbulence which is however always present in the ocean. A reliable DD model for use in OGCMs (ocean global circulation models) is therefore still lacking and a true assessment of the role of oceanic DD is yet to be made. Here, we derive and validate a new model for DD + Turbulence using a second-order closure model which differs significantly from previous ones in that the ratios of the correlation time scales to the dissipation time scales, constant in previous models, now depend on Ri and R r , the key new feature needed to reproduce both laboratory (no shear) and oceanic (with shear) data. The model can therefore be used in OGCMs. The full mixing model includes mixed layer, internal gravity waves, DD and tides.
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Papers by vittorio canuto