scholarly journals A Thermohaline Inverse Method for Estimating Diathermohaline Circulation and Mixing

2014 ◽  
Vol 44 (10) ◽  
pp. 2681-2697 ◽  
Author(s):  
Sjoerd Groeskamp ◽  
Jan D. Zika ◽  
Bernadette M. Sloyan ◽  
Trevor J. McDougall ◽  
Peter C. McIntosh
Keyword(s):  
Diffusion Coefficient ◽  
Inverse Method ◽  
Climate Model ◽  
Salinity Gradient ◽  
Surface Flux ◽  
Volume Transport ◽  
Heat Fluxes ◽  
Small Scale ◽  
Mixing Processes ◽  
Turbulent Diffusion Coefficient

Abstract The thermohaline inverse method (THIM) is presented that provides estimates of the diathermohaline streamfunction , the downgradient along-isopycnal diffusion coefficient K, and the isotropic downgradient turbulent diffusion coefficient D of small-scale mixing processes. This is accomplished by using the water mass transformation framework in two tracer dimensions: here in Absolute Salinity SA and Conservative Temperature Θ coordinates. The authors show that a diathermal volume transport down a Conservative Temperature gradient is related to surface heating and cooling and mixing, and a diahaline volume transport down an Absolute Salinity gradient is related to surface freshwater fluxes and mixing. Both the diahaline and diathermal flows can be calculated using readily observed parameters that are used to produce climatologies, surface flux products, and mixing parameterizations for K and D. Conservation statements for volume, salt, and heat in (SA, Θ) coordinates, using the diahaline and diathermal volume transport expressed as surface freshwater and heat fluxes and mixing, allow for the formulation of a system of equations that is solved by an inverse method that can estimate the unknown diathermohaline streamfunction and the diffusion coefficients K and D. The inverse solution provides an accurate estimate of , K, and D when tested against a numerical climate model for which all these parameters are known.

scholarly journals Air–Sea Turbulent Heat Fluxes in Climate Models and Observational Analyses: What Drives Their Variability?

2019 ◽  
Vol 32 (8) ◽  
pp. 2397-2421 ◽  
Author(s):  
R. Justin Small ◽  
Frank O. Bryan ◽  
Stuart P. Bishop ◽  
Robert A. Tomas
Keyword(s):  
Heat Flux ◽  
Climate Models ◽  
Climate Model ◽  
Turbulent Heat Flux ◽  
Heat Fluxes ◽  
Small Scale ◽  
Turbulent Heat ◽  
Realistic Representation ◽  
Frontal Zones ◽  
The Tropics

Abstract A traditional view is that the ocean outside of the tropics responds passively to atmosphere forcing, which implies that air–sea heat fluxes are mainly driven by atmosphere variability. This paper tests this viewpoint using state-of-the-art air–sea turbulent heat flux observational analyses and a climate model run at different resolutions. It is found that in midlatitude ocean frontal zones the variability of air–sea heat fluxes is not predominantly driven by the atmosphere variations but instead is forced by sea surface temperature (SST) variations arising from intrinsic oceanic variability. Meanwhile in most of the tropics and subtropics wind is the dominant driver of heat flux variability, and atmosphere humidity is mainly important in higher latitudes. The predominance of ocean forcing of heat fluxes found in frontal regions occurs on scales of around 700 km or less. Spatially smoothing the data to larger scales results in the traditional atmosphere-driving case, while filtering to retain only small scales of 5° or less leads to ocean forcing of heat fluxes over most of the globe. All observational analyses examined (1° OAFlux; 0.25° J-OFURO3; 0.25° SeaFlux) show this general behavior. A standard resolution (1°) climate model fails to reproduce the midlatitude, small-scale ocean forcing of heat flux: refining the ocean grid to resolve eddies (0.1°) gives a more realistic representation of ocean forcing but the variability of both SST and of heat flux is too high compared to observational analyses.

ESTIMATE OF DEPENDENCE OF THE VERTICAL TRBULENT DIFFUSION COEFFICIENT FROM BUOYANCY FREQUENCY FOR COASTAL ZONE OF THE BLACK SEA

2017 ◽  
Author(s):  
Lubov Globina ◽  
Lubov Globina
Keyword(s):  
Diffusion Coefficient ◽  
Active Layer ◽  
Black Sea ◽  
Eddy Diffusivity ◽  
The Black Sea ◽  
Small Scale ◽  
Buoyancy Frequency ◽  
Shelf Area ◽  
Turbulent Diffusion Coefficient ◽  
Horizontal Convection

The article highlights the most important studies of oceanographic processes, such as horizontal convection, winter cascading on the shelf and continental slope, the processes in the bottom of the Black Sea. The results of the study of small-scale structure of the shelf upper active layer of the Black Sea in 2014 are discussed. The new information about the distribution of the eddy diffusivity with depth in the coastal part of the Heracleian peninsula is given. The investigated dependence vertical turbulent diffusion coefficient from buoyancy frequency at the active layer is found to be has a quadratic character for the entire shelf area and doesn’t depend on the stratification.

Vertical Wavenumber Spectra of Gravity Waves in the Venus Atmosphere Obtained from Venus Express Radio Occultation Data: Evidence for Saturation

2015 ◽  
Vol 72 (6) ◽  
pp. 2318-2329 ◽  
Author(s):  
Hiroki Ando ◽  
Takeshi Imamura ◽  
Toshitaka Tsuda ◽  
Silvia Tellmann ◽  
Martin Pätzold ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Power Law ◽  
Gravity Waves ◽  
Radio Occultation ◽  
Spectral Power ◽  
European Space Agency ◽  
Small Scale ◽  
Turbulent Diffusion Coefficient ◽  
Venus Express ◽  
Venusian Atmosphere

Abstract By using the vertical temperature profiles obtained by the radio occultation measurements on the European Space Agency (ESA)’s Venus Express, the vertical wavenumber spectra of small-scale temperature fluctuations that are thought to be manifestations of gravity waves are studied. Wavenumber spectra covering wavelengths of 1.4–7.5 km were obtained for two altitude regions (65–80 and 75–90 km) and seven latitude bands. The spectra show a power-law dependence on the high-wavenumber side with the logarithmic spectral slope ranging from −3 to −4, which is similar to the features seen in Earth’s and Martian atmospheres. The power-law portion of the spectrum tends to follow the semiempirical spectrum of saturated gravity waves, suggesting that the gravity waves are dissipated by saturation as well as radiative damping. The spectral power is larger at 75–90 km than at 65–80 km at low wavenumbers, suggesting amplitude growth with height of unsaturated waves. It was also found that the wave amplitude is larger at higher latitudes and that the amplitude is maximized in the northern high latitudes. On the assumption that gravity waves are saturated in the Venusian atmosphere, the turbulent diffusion coefficient was estimated. The diffusion coefficient in the Venusian atmosphere is larger than those in Earth’s atmosphere because of the longer characteristic vertical wavelength of the saturated waves.

ESTIMATE OF DEPENDENCE OF THE VERTICAL TRBULENT DIFFUSION COEFFICIENT FROM BUOYANCY FREQUENCY FOR COASTAL ZONE OF THE BLACK SEA

2017 ◽  
Author(s):  
Lubov Globina ◽  
Lubov Globina
Keyword(s):  
Diffusion Coefficient ◽  
Active Layer ◽  
Black Sea ◽  
Eddy Diffusivity ◽  
The Black Sea ◽  
Small Scale ◽  
Buoyancy Frequency ◽  
Shelf Area ◽  
Turbulent Diffusion Coefficient ◽  
Horizontal Convection

The article highlights the most important studies of oceanographic processes, such as horizontal convection, winter cascading on the shelf and continental slope, the processes in the bottom of the Black Sea. The results of the study of small-scale structure of the shelf upper active layer of the Black Sea in 2014 are discussed. The new information about the distribution of the eddy diffusivity with depth in the coastal part of the Heracleian peninsula is given. The investigated dependence vertical turbulent diffusion coefficient from buoyancy frequency at the active layer is found to be has a quadratic character for the entire shelf area and doesn’t depend on the stratification.

Derivation Of Spreading Parameters Of Oil At Sea For Oil Spill Modeling

2005 ◽  
Vol 2005 (1) ◽  
pp. 681-684
Author(s):  
Kemei Du ◽  
Vikram Kaku ◽  
Michel C. Boufadel ◽  
James Weaver
Keyword(s):  
Diffusion Coefficient ◽  
Oil Spill ◽  
Turbulent Diffusion ◽  
Large Scale ◽  
Oil Spills ◽  
Lateral Spreading ◽  
Small Scale ◽  
Spreading Coefficient ◽  
Turbulent Diffusion Coefficient ◽  
Initial Location

ABSTRACT Oil spill models are commonly used to simulate the large-scale (tens to hundreds of kilometers) transport of oil spills in the oceans. The values of the spreading parameters of these models are obtained empirically by fitting to observed slicks, thus they do not account explicitly for the effects of waves. In addition, there is little success in using these values to predict the spread at smaller scales (tens of meters to a few kilometers). This works attempts to better understand the physics of oil movement in the ocean by focusing on the small-scale mechanisms. The investigation also leads to evaluation of small-scale spreading parameters. The Random Walk Method is used in a Monte Carlo simulation framework to track the transport of oil due to the effects of waves, buoyancy, and turbulent diffusion. The small-scale spreading parameters are then calculated using the Method of Moments. Our results indicated that the approach for using a spreading coefficient becomes after a time equal to about 30 wave periods. This corresponds to a travel of the centroid of about two wave lengths. At larger scales, the longitudinal spreading coefficient increased with distance from the initial location and the lateral spreading coefficient became equal to the turbulent diffusion coefficient. The vertical spreading coefficient reached a value that is smaller than half of the turbulent diffusion coefficient, which is due to the presence of the upper boundary (the free surface) and buoyancy.

A numerical study of the transition of jet diffusion flames

1990 ◽  
Vol 431 (1882) ◽  
pp. 301-314 ◽  
Keyword(s):  
Reynolds Number ◽  
Diffusion Coefficient ◽  
Large Scale ◽  
Numerical Study ◽  
Small Scale ◽  
Surface Model ◽  
Flame Surface ◽  
Transition Mechanism ◽  
Air Stream ◽  
Scale Fluctuation

A numerical study on the transition from laminar to turbulent of two-dimensional fuel jet flames developed in a co-flowing air stream was made by adopting the flame surface model of infinite chemical reaction rate and unit Lewis number. The time dependent compressible Navier–Stokes equation was solved numerically with the equation for coupling function by using a finite difference method. The temperature-dependence of viscosity and diffusion coefficient were taken into account so as to study effects of increases of these coefficients on the transition. The numerical calculation was done for the case when methane is injected into a co-flowing air stream with variable injection Reynolds number up to 2500. When the Reynolds number was smaller than 1000 the flame, as well as the flow, remained laminar in the calculated domain. As the Reynolds number was increased above this value, a transition point appeared along the flame, downstream of which the flame and flow began to fluctuate. Two kinds of fluctuations were observed, a small scale fluctuation near the jet axis and a large scale fluctuation outside the flame surface, both of the same origin, due to the Kelvin–Helmholtz instability. The radial distributions of density and transport coefficients were found to play dominant roles in this instability, and hence in the transition mechanism. The decreased density in the flame accelerated the instability, while the increase in viscosity had a stabilizing effect. However, the most important effect was the increase in diffusion coefficient. The increase shifted the flame surface, where the large density decrease occurs, outside the shear layer of the jet and produced a thick viscous layer surrounding the jet which effectively suppressed the instability.

scholarly journals Averaging-Related Biases in Monthly Latent Heat Fluxes

2012 ◽  
Vol 29 (7) ◽  
pp. 974-986 ◽  
Author(s):  
Paul J. Hughes ◽  
Mark A. Bourassa ◽  
Jeremy J. Rolph ◽  
Shawn R. Smith
Keyword(s):  
Latent Heat ◽  
Classical Method ◽  
Surface Flux ◽  
Heat Fluxes ◽  
Western Boundary ◽  
State University ◽  
Boundary Current ◽  
Surface Energy Fluxes ◽  
Temporal Averaging ◽  
The Impact

Abstract Seasonal-to-multidecadal applications that require ocean surface energy fluxes often require accuracies of surface turbulent fluxes to be 5 W m−2 or better. While there is little doubt that uncertainties in the flux algorithms and input data can cause considerable errors, the impact of temporal averaging has been more controversial. The biases resulting from using monthly averaged winds, temperatures, and humidities in the bulk aerodynamic formula (i.e., the so-called classical method) to estimate the monthly mean latent heat fluxes are shown to be substantial and spatially varying in a manner that is consistent with most prior work. These averaging-related biases are linked to nonnegligible submonthly covariances between the wind, temperature, and humidity. To provide additional insight into the averaging-related bias, the methodology behind the third-generation Florida State University monthly mean surface flux product (FSU3) is detailed to highlight additional sources of errors in gridded datasets. The FSU3 latent heat fluxes suffer from this averaging-related bias, which can be as large as 90 W m−2 in western boundary current regions during winter and can exceed 40 W m−2 in synoptically active portions of the tropics. The regional impacts of these biases on the mixed layer temperature tendency are shown to demonstrate that the error resulting from applying the classical method is physically substantial.

scholarly journals Climate SPHINX: evaluating the impact of resolution and stochastic physics parameterisations in the EC-Earth global climate model

2017 ◽  
Vol 10 (3) ◽  
pp. 1383-1402 ◽  
Author(s):  
Paolo Davini ◽  
Jost von Hardenberg ◽  
Susanna Corti ◽  
Hannah M. Christensen ◽  
Stephan Juricke ◽  
...  
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Climate Model ◽  
Global Climate ◽  
Rainfall Variability ◽  
Global Climate Model ◽  
Small Scale ◽  
Low Resolution ◽  
The Impact ◽  
Stochastic Physics

Abstract. The Climate SPHINX (Stochastic Physics HIgh resolutioN eXperiments) project is a comprehensive set of ensemble simulations aimed at evaluating the sensitivity of present and future climate to model resolution and stochastic parameterisation. The EC-Earth Earth system model is used to explore the impact of stochastic physics in a large ensemble of 30-year climate integrations at five different atmospheric horizontal resolutions (from 125 up to 16 km). The project includes more than 120 simulations in both a historical scenario (1979–2008) and a climate change projection (2039–2068), together with coupled transient runs (1850–2100). A total of 20.4 million core hours have been used, made available from a single year grant from PRACE (the Partnership for Advanced Computing in Europe), and close to 1.5 PB of output data have been produced on SuperMUC IBM Petascale System at the Leibniz Supercomputing Centre (LRZ) in Garching, Germany. About 140 TB of post-processed data are stored on the CINECA supercomputing centre archives and are freely accessible to the community thanks to an EUDAT data pilot project. This paper presents the technical and scientific set-up of the experiments, including the details on the forcing used for the simulations performed, defining the SPHINX v1.0 protocol. In addition, an overview of preliminary results is given. An improvement in the simulation of Euro-Atlantic atmospheric blocking following resolution increase is observed. It is also shown that including stochastic parameterisation in the low-resolution runs helps to improve some aspects of the tropical climate – specifically the Madden–Julian Oscillation and the tropical rainfall variability. These findings show the importance of representing the impact of small-scale processes on the large-scale climate variability either explicitly (with high-resolution simulations) or stochastically (in low-resolution simulations).

The Tropical Transition of the October 1996 Medicane in the Western Mediterranean Sea: A Warm Seclusion Event

2017 ◽  
Vol 145 (7) ◽  
pp. 2575-2595 ◽  
Author(s):  
Edoardo Mazza ◽  
Uwe Ulbrich ◽  
Rupert Klein
Keyword(s):  
Wind Shear ◽  
Climate Model ◽  
Regional Climate ◽  
Vertical Wind Shear ◽  
Lower Troposphere ◽  
Western Mediterranean ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Western Mediterranean Sea ◽  
Warm Core

The processes leading to the tropical transition of the October 1996 medicane in the western Mediterranean are investigated on the basis of a 50-member ensemble of regional climate model (RCM) simulations. By comparing the composites of transitioning and nontransitioning cyclones it is shown that standard extratropical dynamics are responsible for the cyclogenesis and that the transition results from a warm seclusion process. As the initial thermal asymmetries and vertical tilt of the cyclones are reduced, a warm core forms in the lower troposphere. It is demonstrated that in the transitioning cyclones, the upper-tropospheric warm core is also a result of the seclusion process. Conversely, the warm core remains confined below 600 hPa in the nontransitioning systems. In the baroclinic stage, the transitioning cyclones are characterized by larger vertical wind shear and intensification rates. The resulting stronger low-level circulation in turn is responsible for significantly larger latent and sensible heat fluxes throughout the seclusion process.

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