A Pressure-Invariant Neutral Density Variable for the World's Oceans

2020 ◽  
Vol 50 (12) ◽  
pp. 3585-3604
Author(s):  
Yandong Lang ◽  
Geoffrey J. Stanley ◽  
Trevor J. McDougall ◽  
Paul M. Barker
Keyword(s):  
Tangent Plane ◽  
Neutral Density ◽  
Potential Density ◽  
Neutral Buoyancy ◽  
Material Derivative ◽  
Water Columns ◽  
Density Values ◽  
Coherent Vortex ◽  
High Resolution Models ◽  
Water Parcel

AbstractWe present a new method to calculate the neutral density of an arbitrary water parcel. Using this method, the value of neutral density depends only on the parcel’s salinity, temperature, latitude, and longitude and is independent of the pressure (or depth) of the parcel, and is therefore independent of heave in observations or high-resolution models. In this method we move the parcel adiabatically and isentropically like a submesoscale coherent vortex (SCV) to its level of neutral buoyancy on four nearby water columns of a climatological atlas. The parcel’s neutral density γSCV is interpolated from prelabeled neutral density values at these four reference locations in the climatological atlas. This method is similar to the neutral density variable γn of Jackett and McDougall: their discretization of the neutral relationship equated the potential density of two parcels referenced to their average pressure, whereas our discretization equates the parcels’ potential density referenced to the pressure of the climatological parcel. We calculate the numerical differences between γSCV and γn, and we find similar variations of γn and γSCV on the ω surfaces of Klocker, McDougall, and Jackett. We also find that isosurfaces of γn and γSCV deviate from the neutral tangent plane by similar amounts. We compare the material derivative of γSCV with that of γn, finding their total material derivatives are of a similar magnitude.

Impact of electron density values from space-geodetic observation techniques on thermospheric density models

2020 ◽  
Author(s):  
Armin Corbin ◽  
Kristin Vielberg ◽  
Michael Schmidt ◽  
Jürgen Kusche
Keyword(s):  
Electron Density ◽  
Orbit Determination ◽  
General Circulation ◽  
Precise Orbit Determination ◽  
Circulation Model ◽  
Physical Models ◽  
Neutral Density ◽  
Atmospheric Drag ◽  
Electron Densities ◽  
Density Values

<p><span>The neutral density in the thermosphere is directly related to the atmospheric drag acceleration acting on satellites. In fact, the atmospheric drag acceleration, is the largest non-gravitational perturbation for satellites below 1000 km that has to be considered for precise orbit determination. There are several global empirical and physical models providing the neutral density in the thermosphere. However, there are significant differences between the modeled neutral densities and densities observed via accelerometers. More precise thermospheric density models are required for improving drag modeling as well as orbit determination. We study the coupling between ionosphere and thermosphere based on observations and model outputs of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM). At first, we analyse the model’s representation of the coupling using electron and neutral densities. In comparison, we study the coupling based on observations, i.e., accelerometer-derived neutral densities and electron densities from a 4D electron density model based on GNSS and satellite altimetry data as well as radio occultation measurements. We expect that increased electron densities can be related to increased neutral densities. This is indicated for example by a correlation of approximately 55% between the neutral densities and the electron densities computed by the TIE-GCM. Finally, we investigate whether neutral density simulations fit better to in-situ densities from accelerometry when electron densities are assimilated.</span></p>

scholarly journals A new method for forming approximately neutral surfaces

2008 ◽  
Vol 5 (3) ◽  
pp. 419-470
Author(s):  
A. Klocker ◽  
T. J. McDougall ◽  
D. R. Jackett
Keyword(s):  
Ocean Circulation ◽  
Simple Algorithm ◽  
New Method ◽  
Neutral Density ◽  
Potential Density ◽  
Diapycnal Diffusivity ◽  
Layered Models

Abstract. We introduce a simple algorithm to improve existing density surfaces to ensure that the resulting surfaces are as close to neutral as possible. This means the slopes at any point on the surfaces are close to neutral tangent planes – the directions along which layered stirring and mixing occurs – minimizing the fictitious diapycnal diffusivity. Inverse techniques and layered models have been used for decades to understand ocean circulation. The most-used density surfaces are potential density or neutral density surfaces. Both these density surfaces and all others produce a fictitious diapycnal diffusivity to some degree due to the helical nature of neutral trajectories – with the magnitude of this artificial diffusivity in some cases being larger than the values measured in the ocean. Here we show how this error can be reduced by up to four orders of magnitude and therefore becomes insignificant compared to measured values, thus providing surfaces which would produce more accurate results when used for inverse techniques.

The material derivative of neutral density

2005 ◽  
Vol 63 (1) ◽  
pp. 159-185 ◽  
Author(s):  
Trevor J. McDougall ◽  
David R. Jackett
Keyword(s):  
Neutral Density ◽  
Material Derivative

The Materiality and Neutrality of Neutral Density and Orthobaric Density

2009 ◽  
Vol 39 (8) ◽  
pp. 1779-1799 ◽  
Author(s):  
Roland A. de Szoeke ◽  
Scott R. Springer
Keyword(s):  
Spatial Variation ◽  
Vertical Velocity ◽  
Water Mass ◽  
Neutral Density ◽  
Type I ◽  
Type Ii ◽  
Material Derivative ◽  
Mass Properties ◽  
Local Reference ◽  
The Difference

Abstract The materiality and neutrality of neutral density and several forms of orthobaric density are calculated and compared using a simple idealization of the warm-sphere water mass properties of the Atlantic Ocean. Materiality is the value of the material derivative, expressed as a quasi-vertical velocity, following the motion of each of the variables: zero materiality denotes perfect conservation. Neutrality is the difference between the dip in the isopleth surfaces of the respective variables and the dip in the neutral planes. The materiality and neutrality of the neutral density of a water sample are composed of contributions from the following: (I) how closely the sample’s temperature and salinity lie in relation to the local reference θ–S relation, (II) the spatial variation of the reference θ–S relation, (III) the neutrality of the underlying reference neutral density surfaces, and (IV) irreversible exchanges of heat and salinity. Type II contributions dominate but have been neglected in previous assessments of neutral density properties. The materiality and neutrality of surfaces of simple orthobaric density, defined using a spatially uniform θ–S relation, have contributions analogous to types I and IV, but lack any of types II or III. Extending the concept of orthobaric density to permit spatial variation of the θ–S relation diminishes the type I contributions, but the effect is counterbalanced by the emergence of type II contributions. Discrete analogs of extended orthobaric density, based on regionally averaged θ–S relations matched at interregional boundaries, reveal a close analogy between the extended orthobaric density and the practical neutral density. Neutral density is not superior, even to simple orthobaric density, in terms of materiality or neutrality.

Does lateral stirring really take place along neutral surfaces in double-diffusive regions of the oceans?

2020 ◽  
Author(s):  
Gabriel Wolf ◽  
Tailleux Remi ◽  
Ferreira David ◽  
Kuhlbrodt Till
Keyword(s):  
Ad Hoc ◽  
Climate Models ◽  
Potential Temperature ◽  
Water Masses ◽  
Neutral Density ◽  
Positive Density ◽  
Potential Density ◽  
Source Regions ◽  
Density Ratios ◽  
Double Diffusive

<p><span>Potential temperature/salinity (theta/S) characteristics of water masses in the ocean interior can often be traced back over long distances to their source regions. In practice, understanding how water masses are altered by interior mixing and stirring requires a detailed understanding of the interior pathways linking fluid parcels to their source regions. So far, oceanographers have generally assumed that these pathways are strongly constrained to take place on potential density surfaces of some kind, of which the most commonly employed have been the Jackett and McDougall neutral density variable and sigma2, the potential density referenced to 2000 dbar. Because sigma2 is a somewhat ad-hoc and artificial construct, the more physically-based neutral density variable has been widely assumed to represent the most accurate variable to describe interior pathways, but the analysis of van Sebille et al. (2011) intriguingly suggests otherwise. In order to shed light on the issue, this work hypothesizes that if neutral surfaces were optimal to describe lateral stirring in the ocean, they should be the surfaces along which the observed spread in potential temperature and salinity anomalies should be minimum, since lateral stirring is about 7 orders of magnitude more vigorous in the lateral directions than perpendicular to them. Surprisingly, it is found that this is actually never the case in ocean regions with positive density ratios, traditionally associated with double-diffusive regimes. In those regions, indeed, it is always possible to find material surfaces, not necessarily definable in terms of potential density, along which the spread is reduced for both potential temperature and salinity compared to that over neutral surfaces. In doubly-stable regions, on the other hand, it is not possible to find material variables able to simultaneously reduce both the spread in potential temperature and salinity compared to that over neutral surfaces. Given the widespread nature of double-diffusive regimes in the world oceans, especially in the Atlantic Ocean, these results have strong implications for the ability of ocean climate models to accurately simulate water masses, as it is unclear how to maintain water masses properties by mixing vigorously along directions along which the spread in theta/S is far from its minimum.</span></p>

scholarly journals A new method for forming approximately neutral surfaces

Ocean Science ◽  
2009 ◽  
Vol 5 (2) ◽  
pp. 155-172 ◽  
Author(s):  
A. Klocker ◽  
T. J. McDougall ◽  
D. R. Jackett
Keyword(s):  
Ocean Circulation ◽  
Simple Algorithm ◽  
New Method ◽  
Neutral Density ◽  
Potential Density ◽  
Diapycnal Diffusivity ◽  
Layered Models

Abstract. We introduce a simple algorithm to improve existing density surfaces to ensure that the resulting surfaces are as close to neutral as possible. This means the slopes at any point on the surfaces are close to neutral tangent planes – the directions along which layered stirring and mixing occurs – minimizing the fictitious diapycnal diffusivity. Inverse techniques and layered models have been used for decades to understand ocean circulation. The most-used density surfaces are potential density or neutral density surfaces. Both these density surfaces and all others produce a fictitious diapycnal diffusivity to some degree due to the helical nature of neutral trajectories – with the magnitude of this artificial diffusivity in some cases being larger than the values measured in the ocean. Here we show how this error can be reduced by up to four orders of magnitude and therefore becomes insignificant compared to measured values, thus providing surfaces which would produce more accurate results when used for inverse techniques.

scholarly journals Generalized Patched Potential Density and Thermodynamic Neutral Density: Two New Physically Based Quasi-Neutral Density Variables for Ocean Water Masses Analyses and Circulation Studies

2016 ◽  
Vol 46 (12) ◽  
pp. 3571-3584 ◽  
Author(s):  
Rémi Tailleux
Keyword(s):  
Ocean Circulation ◽  
Water Masses ◽  
Actual State ◽  
Neutral Density ◽  
Polar Regions ◽  
Potential Density ◽  
Material Density ◽  
Vertical Coordinate ◽  
Rational Polynomial ◽  
Physically Based

AbstractIn this paper, two new quasi-neutral density variables—generalized patched potential density (GPPD) and thermodynamic neutral density γT—are introduced, which are showed to approximate Jackett and McDougall empirical neutral density γn significantly better than the quasi-material rational polynomial approximation γa previously introduced by McDougall and Jackett. In contrast to γn, γT is easily and efficiently computed for arbitrary climatologies of temperature and salinity (both realistic and idealized), has a clear physical basis rooted in the theory of available potential energy, and does not suffer from nonmaterial effects that make γn so difficult to use in water masses analysis. In addition, γT is also significantly more neutral than all known quasi-material density variables, such as σ2, while remaining less neutral than γn. Because unlike γn, γT is mathematically explicit, it can be used for theoretical as well as observational studies, as well as a generalized vertical coordinate in isopycnal models of the ocean circulation. On the downside, γT exhibits inversions and degraded neutrality in the polar regions, where the Lorenz reference state is the furthest away from the actual state. Therefore, while γT represents progress over previous approaches, further work is still needed to determine whether its polar deficiencies can be corrected, an essential requirement for γT to be useful in Southern Ocean studies, for instance.

scholarly journals Climatological mean distribution of specific entropy in the oceans

2007 ◽  
Vol 4 (1) ◽  
pp. 129-144
Author(s):  
Z. Gan ◽  
Y. Yan ◽  
Y. Qi
Keyword(s):  
Potential Temperature ◽  
Temporal Distribution ◽  
Neutral Density ◽  
State Function ◽  
Physical Oceanography ◽  
Potential Density ◽  
Specific Entropy ◽  
Traditional Assumption ◽  
Important State ◽  
Insight Into

Abstract. Entropy as an important state function can be considered to provide insight into the thermodynamic properties of seawater. In this paper, the spatial-temporal distribution of specific entropy in the oceans is presented, using a new Gibbs thermodynamic potential function of seawater, which is proposed by R. Feistel. An important result is found that the distribution of specific entropy is surprisingly different from that of potential density or neutral density surfaces. By contrast, the distribution of specific entropy is quite similar to that of potential temperature in the oceans. This result is not consistent with the traditional assumption that isopycnal or isoneutral surfaces could be approximately regarded as isentropic surfaces in the physical oceanography.

Microstructural Development in Nb-Ti Multifilamentary Superconductors During Processing

1985 ◽  
Vol 43 ◽  
pp. 190-191
Author(s):  
A. W. West
Keyword(s):  
Heat Treatment ◽  
Critical Current Density ◽  
Copper Matrix ◽  
Wire Drawing ◽  
Heat Treatments ◽  
Microstructural Development ◽  
Final Size ◽  
Density Values ◽  
The Wire ◽  
Multifilamentary Superconductors

The influence of the filament microstructure on the critical current density values, Jc, of Nb-Ti multifilamentary superconducting composites has been well documented. However the development of these microstructures during composite processing is still under investigation.During manufacture, the multifilamentary composite is given several heat treatments interspersed in the wire-drawing schedule. Typically, these heat treatments are for 5 to 80 hours at temperatures between 523 and 573K. A short heat treatment of approximately 3 hours at 573K is usually given to the wire at final size. Originally this heat treatment was given to soften the copper matrix, but recent work has shown that it can markedly change both the Jc value and microstructure of the composite.

Facet Topography and Dislocation Structure as a Possible Source for Electrical Heterogeneity in [001] TILT Bicrystals of YBa2Cu3O7-δ

1996 ◽  
Vol 54 ◽  
pp. 338-339
Author(s):  
I-Fei Tsu ◽  
D.L. Kaiser ◽  
S.E. Babcock
Keyword(s):  
Grain Boundary ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Electromagnetic Properties ◽  
Length Scale ◽  
Density Values ◽  
Current Densities ◽  
Applied Fields ◽  
A Current

A current theme in the study of the critical current density behavior of YBa2Cu3O7-δ (YBCO) grain boundaries is that their electromagnetic properties are heterogeneous on various length scales ranging from 10s of microns to ˜ 1 Å. Recently, combined electromagnetic and TEM studies on four flux-grown bicrystals have demonstrated a direct correlation between the length scale of the boundaries’ saw-tooth facet configurations and the apparent length scale of the electrical heterogeneity. In that work, enhanced critical current densities are observed at applied fields where the facet period is commensurate with the spacing of the Abrikosov flux vortices which must be pinned if higher critical current density values are recorded. To understand the microstructural origin of the flux pinning, the grain boundary topography and grain boundary dislocation (GBD) network structure of [001] tilt YBCO bicrystals were studied by TEM and HRTEM.

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