scholarly journals Mesoscale Eddy Energy Locality in an Idealized Ocean Model

2013 ◽  
Vol 43 (9) ◽  
pp. 1911-1923 ◽  
Author(s):  
Ian Grooms ◽  
Louis-Philippe Nadeau ◽  
K. Shafer Smith
Keyword(s):  
Energy Budget ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Spatial Filter ◽  
Ocean Model ◽  
Energy Budgets ◽  
Subgrid Scale ◽  
Common Time ◽  
Local Functions ◽  
The Mean

Abstract This paper investigates the energy budget of mesoscale eddies in wind-driven two-layer quasigeostrophic simulations. Intuitively, eddy energy can be generated, dissipated, and fluxed from place to place; regions where the budget balances generation and dissipation are “local” and regions that export or import large amounts of eddy energy are “nonlocal.” Many mesoscale parameterizations assume that statistics of the unresolved eddies behave as local functions of the resolved large scales, and studies that relate doubly periodic simulations to ocean patches must assume that the ocean patches have local energetics. This study derives and diagnoses the eddy energy budget in simulations of wind-driven gyres. To more closely approximate the ideas of subgrid-scale parameterization, the authors define the mean and eddies using a spatial filter rather than the more common time average. The eddy energy budget is strongly nonlocal over nearly half the domain in the simulations. In particular, in the intergyre region the eddies lose energy through interactions with the mean, and this energy loss can only be compensated by nonlocal flux of energy from elsewhere in the domain. This study also runs doubly periodic simulations corresponding to ocean patches from basin simulations. The eddy energy level of ocean patches in the basin simulations matches the level in the periodic simulations only in regions with local eddy energy budgets.

The Effects of Mesoscale Eddies on the Main Subtropical Thermocline

2004 ◽  
Vol 34 (11) ◽  
pp. 2428-2443 ◽  
Author(s):  
Cara C. Henning ◽  
Geoffrey K. Vallis
Keyword(s):  
Mixed Layer ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Western Boundary ◽  
Residual Circulation ◽  
Mean Flow ◽  
Vertical Diffusion ◽  
Mode Water ◽  
Water Region ◽  
The Mean

Abstract The effects of mesoscale eddies on the main subtropical thermocline are explored using a simply configured wind- and buoyancy-driven primitive equation numerical model in conjunction with transformed Eulerian mean diagnostics and simple scaling ideas and closure schemes. If eddies are suppressed by a modest but nonnegligible horizontal diffusion and vertical diffusion is kept realistically small, the model thermocline exhibits a familiar two-regime structure with an upper, advectively dominated ventilated thermocline and a lower, advective– diffusive internal thermocline, and together these compose the main thermocline. If the horizontal resolution is sufficiently high and the horizontal diffusivity is sufficiently low, then a vigorous mesoscale eddy field emerges. In the mixed layer and upper-mode-water regions, the divergent eddy fluxes are manifestly across isopycnals and so have a diabatic effect. Beneath the mixed layer, the mean structure of the upper (i.e., ventilated) thermocline is still found to be dominated by mean advective terms, except in the “mode water” region and close to the western boundary current. The eddies are particularly strong in the mode-water region, and the low-potential-vorticity pool of the noneddying case is partially eroded away as the eddies try to flatten the isopycnals and reduce available potential energy. The intensity of the eddies decays with depth more slowly than does the mean flow, leading to a three-way balance among eddy flux convergence, mean flow advection, and diffusion in the internal thermocline. Eddies subduct water along isopycnals from the surface into the internal thermocline, replenishing its water masses and maintaining its thickness. Just as in the noneddying case, the dynamics of the internal thermocline can be usefully expressed as an advective–diffusive balance, but where advection is now by the residual (eddy-induced plus Eulerian mean) circulation. The eddy-induced advection partially balances the mean upwelling through the base of the thermocline, and this leads to a slightly thicker thermocline than in the noneddying case. The results suggest that as the diffusivity goes to zero, the residual circulation will go to zero but the thickness of the internal thermocline may remain finite, provided eddy activity persists.

scholarly journals On the Fluctuating Buoyancy Fluxes Simulated in a OGCM

2013 ◽  
Vol 43 (7) ◽  
pp. 1270-1287 ◽  
Author(s):  
Hongmei Li ◽  
Jin-Song von Storch
Keyword(s):  
Climate Models ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Ocean Modeling ◽  
Subgrid Scale ◽  
Inertial Waves ◽  
Basic Properties ◽  
Tropical Instability Waves ◽  
Order Of Magnitude ◽  
Hourly Output

Abstract Subgrid-scale fluctuations with zero means have generally been neglected in ocean modeling, despite their potential role in affecting the oceanic state following Hasselmann's seminal paper on stochastic climate models and series of studies conducted thereafter. When representing effects of these fluctuations in a stochastic parameterization, knowledge of basic properties of these fluctuations is essential. Here, the authors quantify these properties using hourly output of a simulation performed with a global OGCM. This study found that fluctuating buoyancy fluxes are strong in the sense that their strengths are up to one order of magnitude larger than the magnitudes of the respective mean eddy fluxes and that the fluctuations originate not only from mesoscale eddies and tropical instability waves but also from near-inertial waves, especially in the low- and midlatitude oceans. It is this wave contribution that makes the basic properties of fluctuations distinctly different from those expected from mesoscale eddies. The geographical distribution of fluctuation intensity differs from that of mesoscale eddy activity and is strongest in the low- and midlatitude oceans complemented by additional and secondary maxima in the Gulf Stream, the Kuroshio, and the Southern Ocean. The seasonality in most of the low- and midlatitude oceans, characterized by stronger fluctuations in winter than in summer, is just the opposite of that of mesoscale eddies. In the tropical oceans, the correlation length scales reach 500 km in the zonal direction but only about 30–40 km in the meridional direction, reflecting near-inertial waves with nearly zonally oriented wavecrests. Overall, these results provide an important basis for stochastically describing the effects of subgrid-scale fluctuations.

scholarly journals An Energy Conservation Analysis of Ocean Drift in the CMIP5 Global Coupled Models*

2016 ◽  
Vol 29 (5) ◽  
pp. 1639-1653 ◽  
Author(s):  
Will Hobbs ◽  
Matthew D. Palmer ◽  
Didier Monselesan
Keyword(s):  
Energy Budget ◽  
Climate Model ◽  
Heat Content ◽  
Ocean Model ◽  
Future Climate Change ◽  
Energy Budgets ◽  
State Variables ◽  
Coupled Models ◽  
Significant Disagreement ◽  
Climate Model Simulations

Abstract Climate model simulations of changes to Earth’s energy budget are fundamental to improve understanding of both historical and future climate change. However, coupled models are prone to “drift” (i.e., they contain spurious unforced trends in state variables) due to incomplete spinup or nonclosure of the energy budget. This work assesses the globally integrated energy budgets of 25 models in phase 5 of CMIP (CMIP5). It is shown that for many of the models there is a significant disagreement between ocean heat content changes and net top-of-atmosphere radiation. The disagreement is largely time-constant and independent of forcing scenario. Furthermore, most of the nonconservation seems to occur as a result of energy leaks external to the ocean model realm. After drift correction, the time-varying energy budget is consistent at decadal time scales, and model responses to climate forcing are not sensitive to the magnitude of their drift. This demonstrates that, although drift terms can be significant, model output can be corrected post hoc without biasing results.

scholarly journals Toward Energetically Consistent Ocean Models

2014 ◽  
Vol 44 (12) ◽  
pp. 3160-3184 ◽  
Author(s):  
Carsten Eden ◽  
Lars Czeschel ◽  
Dirk Olbers
Keyword(s):  
Energy Input ◽  
Large Scale ◽  
Mesoscale Eddy ◽  
Boussinesq Approximation ◽  
Ocean Model ◽  
Global Ocean ◽  
External Energy ◽  
Large Scale Circulation ◽  
Consistent Model ◽  
The Mean

Abstract Possibilities to construct a realistic quasi-global ocean model in Boussinesq approximation with a closed energy cycle are explored in this study. In such a model, the energy related to the mean variables would interact with all parameterized forms of energy without any spurious energy sources or sinks. This means that the energy available for interior mixing in the ocean would be only controlled by external energy input from the atmosphere and the tidal system and by internal exchanges. In the current implementation of such a consistent model, however, numerical biases and sources due to the nonlinear equation of state violate energy conservation, resulting in an overall residual up to several percent. In three (approximately) consistent model versions with different scenarios of mesoscale eddy dissipation, the parameterized internal wave field provides between 2 and 3 TW for interior mixing from the total external energy input of about 4 TW, such that a transfer between 0.3 and 0.4 TW into mean potential energy contributes to drive the large-scale circulation in the model. In contrast, the wind work on the mean circulation contributes by about 1.8 TW to the large-scale circulation in all model versions. It is shown that the consistent model versions are more energetic than standard and inconsistent model versions and in better agreement with hydrographic observations.

The Mechanical Energy Budget of a Regional Ocean Model

2016 ◽  
Vol 46 (9) ◽  
pp. 2719-2733 ◽  
Author(s):  
Parker MacCready ◽  
Sarah N. Giddings
Keyword(s):  
Seasonal Variation ◽  
Energy Budget ◽  
Coastal Upwelling ◽  
Mechanical Energy ◽  
Realistic Model ◽  
Ocean Model ◽  
Energy Budgets ◽  
Estuarine System ◽  
Salish Sea ◽  
Definition Of

AbstractA method is presented for calculating a complete, numerically closed, mechanical energy budget in a realistic simulation of circulation in a coastal–estuarine domain. The budget is formulated in terms of the “local” available potential energy (APE; Holliday and McIntyre 1981). The APE may be split up into two parts based on whether a water parcel has been displaced up or down relative to its rest depth. This decomposition clearly shows the different APE signatures of coastal upwelling (particles displaced up by wind) and the estuary (particles displaced down by mixing). Because the definition of APE is local in almost the same sense that kinetic energy is, this study may form meaningful integrals of reservoir and budget terms even over regions that have open boundaries. However, the choice of volume to use for calculation of the rest state is not unique and may influence the results. Complete volume-integrated energy budgets over shelf and estuary volumes in a realistic model of the northeast Pacific and Salish Sea give a new way to quantify the state of these systems and the physical forces that influence that state. On the continental shelf, upwelling may be quantified using APE, which is found to have order-one seasonal variation with an increase due to winds and decrease due to mixing. In the Salish Sea estuarine system, the APE has much less seasonal variation, and the magnitude of the most important forcing terms would take over 7 months to fully drain this energy.

scholarly journals The features of the coastal fronts in the Eastern Guangdong coastal waters during the downwelling-favorable wind period

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chaoyu Yang ◽  
Haibin Ye
Keyword(s):  
Coastal Waters ◽  
Meteorological Data ◽  
Pearson Correlation ◽  
Ocean Model ◽  
Ekman Pumping ◽  
Zonal Distribution ◽  
Factors Affecting ◽  
China Sea ◽  
Hybrid Coordinate Ocean Model ◽  
The Mean

AbstractA coastal front was detected in the eastern Guangdong (EGD) coastal waters during a downwelling-favorable wind period by using the diffuse attenuation coefficient at 490 nm (Kd(490)). Long-term satellite data, meteorological data and hydrographic data collected from 2003 to 2017 were jointly utilized to analyze the environmental factors affecting coastal fronts. The intensities of the coastal fronts were found to be associated with the downwelling intensity. The monthly mean Kd(490) anomalies in shallow coastal waters less than 25 m deep along the EGD coast and the monthly mean Ekman pumping velocities retrieved by the ERA5 dataset were negatively correlated, with a Pearson correlation of − 0.71. The fronts started in October, became weaker and gradually disappeared after January, extending southwestward from the southeastern coast of Guangdong Province to the Wanshan Archipelago in the South China Sea (SCS). The cross-frontal differences in the mean Kd(490) values could reach 3.7 m−1. Noticeable peaks were found in the meridional distribution of the mean Kd(490) values at 22.5°N and 22.2°N and in the zonal distribution of the mean Kd(490) values at 114.7°E and 114.4°E. The peaks tended to narrow as the latitude increased. The average coastal surface currents obtained from the global Hybrid Coordinate Ocean Model (HYCOM) showed that waters with high nutrient and sediment contents in the Fujian and Zhejiang coastal areas in the southern part of the East China Sea could flow into the SCS. The directions and lengths of the fronts were found to be associated with the flow advection.

Mesoscale eddies in the Black Sea: Characteristics and kinematic properties in a high-resolution ocean model

2021 ◽  
pp. 103613
Author(s):  
Ehsan Sadighrad ◽  
Bettina A. Fach ◽  
Sinan S. Arkin ◽  
Baris Salihoğlu ◽  
Sinan Hüsrevoğlu
Keyword(s):  
High Resolution ◽  
Black Sea ◽  
Mesoscale Eddies ◽  
Ocean Model ◽  
The Black Sea ◽  
Kinematic Properties

Earth's balanced climates in view of their energy budgets

2021 ◽  
Author(s):  
Thomas Anderl
Keyword(s):  
Water Vapor ◽  
Surface Temperature ◽  
Energy Budget ◽  
Energy Budgets ◽  
Temperature Dependency ◽  
Energy Balancing ◽  
Atmospheric Water ◽  
Atmospheric Absorption ◽  
Rainfall Events ◽  
Characteristic Concentration

Abstract Earth’s well-known energy budget scheme is subjected to variations representing changes of insolation and atmospheric absorption. The Charney Report variability cases of doubled atmospheric CO2 concentration and insolation increase by 2 % are found reproducible. The planetary emissivity is revealed linear to surface temperature, conformant with measurements. Atmospheric water vapor with its characteristic concentration-temperature dependency appears as a major component in Earth’s energy balancing mechanisms. From this, shift towards fewer and stronger rainfall events is prescribed for rising temperatures.

scholarly journals Impact of Resolution on the Tropical Pacific Circulation in a Matrix of Coupled Models

2009 ◽  
Vol 22 (10) ◽  
pp. 2541-2556 ◽  
Author(s):  
Malcolm J. Roberts ◽  
A. Clayton ◽  
M.-E. Demory ◽  
J. Donners ◽  
P. L. Vidale ◽  
...  
Keyword(s):  
Coupled Model ◽  
Walker Circulation ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Coupled Models ◽  
Model Stability ◽  
The Mean ◽  
The Impact ◽  
Mean State ◽  
The Tropical Pacific

Abstract Results are presented from a matrix of coupled model integrations, using atmosphere resolutions of 135 and 90 km, and ocean resolutions of 1° and 1/3°, to study the impact of resolution on simulated climate. The mean state of the tropical Pacific is found to be improved in the models with a higher ocean resolution. Such an improved mean state arises from the development of tropical instability waves, which are poorly resolved at low resolution; these waves reduce the equatorial cold tongue bias. The improved ocean state also allows for a better simulation of the atmospheric Walker circulation. Several sensitivity studies have been performed to further understand the processes involved in the different component models. Significantly decreasing the horizontal momentum dissipation in the coupled model with the lower-resolution ocean has benefits for the mean tropical Pacific climate, but decreases model stability. Increasing the momentum dissipation in the coupled model with the higher-resolution ocean degrades the simulation toward that of the lower-resolution ocean. These results suggest that enhanced ocean model resolution can have important benefits for the climatology of both the atmosphere and ocean components of the coupled model, and that some of these benefits may be achievable at lower ocean resolution, if the model formulation allows.

scholarly journals The influence of idealized surface heterogeneity on virtual turbulent flux measurements

2018 ◽  
Vol 18 (7) ◽  
pp. 5059-5074 ◽  
Author(s):  
Frederik De Roo ◽  
Matthias Mauder
Keyword(s):  
Energy Budget ◽  
Turbulent Flux ◽  
Surface Heterogeneity ◽  
Surface Fluxes ◽  
Convective Conditions ◽  
Mean Flow ◽  
Flux Divergence ◽  
Length Scales ◽  
Flux Measurements ◽  
The Mean

Abstract. The imbalance of the surface energy budget in eddy-covariance measurements is still an unsolved problem. A possible cause is the presence of land surface heterogeneity, which affects the boundary-layer turbulence. To investigate the impact of surface variables on the partitioning of the energy budget of flux measurements in the surface layer under convective conditions, we set up a systematic parameter study by means of large-eddy simulation. For the study we use a virtual control volume approach, which allows the determination of advection by the mean flow, flux-divergence and storage terms of the energy budget at the virtual measurement site, in addition to the standard turbulent flux. We focus on the heterogeneity of the surface fluxes and keep the topography flat. The surface fluxes vary locally in intensity and these patches have different length scales. Intensity and length scales can vary for the two horizontal dimensions but follow an idealized chessboard pattern. Our main focus lies on surface heterogeneity of the kilometer scale, and one order of magnitude smaller. For these two length scales, we investigate the average response of the fluxes at a number of virtual towers, when varying the heterogeneity length within the length scale and when varying the contrast between the different patches. For each simulation, virtual measurement towers were positioned at functionally different positions (e.g., downdraft region, updraft region, at border between domains, etc.). As the storage term is always small, the non-closure is given by the sum of the advection by the mean flow and the flux-divergence. Remarkably, the missing flux can be described by either the advection by the mean flow or the flux-divergence separately, because the latter two have a high correlation with each other. For kilometer scale heterogeneity, we notice a clear dependence of the updrafts and downdrafts on the surface heterogeneity and likewise we also see a dependence of the energy partitioning on the tower location. For the hectometer scale, we do not notice such a clear dependence. Finally, we seek correlators for the energy balance ratio in the simulations. The correlation with the friction velocity is less pronounced than previously found, but this is likely due to our concentration on effectively strongly to freely convective conditions.

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