56 research outputs found
Global characterization of the ocean's internal gravity wave vertical wavenumber spectrum from Argo float profiles
No full textOceanic internal gravity wave energy levels E (m^2/s^2), vertical wavenumber spectral slopes s, and vertical wavenumber scale m* (1/m) estimated by fitting the Garrett Munk model vertical wavenumber shape function to strain spectra obtained from Argo float hydrographic profiles based on the finestructure method, as discussed in Pollmann (2020): "Global Characterization of the Ocean’s Internal Wave Spectrum" (Journal of Physical Oceanography 50.7: 1871-1891). The paper and hence this dataset are a contribution to the Collaborative Research Centre TRR181 ‘Energy Transfers in Atmosphere and Ocean’ funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Projektnummer 274762653. The hydrographic profiles used in this study were collected and made freely available by the International Argo Program and the national programs that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org). The Argo Program is part of the Global Ocean Observing System.
Please cite Pollmann (2020) when using this dataset.
This dataset includes:
a) energy density (m^2/s^2) binned into 1°x1° horizontal bins and averaged into 3 depth bins (300-500 m, 500-1000 m, 1000-2000 m)
b) vertical wavenumber spectral slopes binned into 1°x1° horizontal bins and averaged into 3 depth bins (300-500 m, 500-1000 m, 1000-2000 m)
c) vertical wavenumber scale m* (1/m) binned into 1°x1° horizontal bins and averaged into 3 depth bins (300-500 m, 500-1000 m, 1000-2000 m)
d) latitude and longitude, defined such that, e.g., E(10,10) represents energy levels in the bin bounded by lat(10), lat(11) as well as lon(10), lon(11
How to Flatter the Laity? Rethinking Catholic Responses to the Reformation (discussiedossier over Catholic Identity and the Revolt of the Netherlands, 1520-1635)
No full textThis rejoinder summarises the two main questions which Catholic Identity and the Revolt of the Netherlands, 1520-1635 seeks to address, and explains the way in which the author approached these before engaging with the points raised by the three reviewers. Noting the reviewers’ appreciation for the book’s emphasis on the experience of the laity and their role in the Catholic revival, the rejoinder discusses the points of criticism they raised, as well as the potential for further research.
Encouraging the reader not to be deceived by the smokescreen of uniformity and hierarchy which the post-Tridentine Catholic Church has drawn up, the author suggests that we can account much more satisfactorily for the curious changes in fortune of the Catholic Church by looking beyond institutional sources, by appreciating the virtues of fragmentation and by broadening our scope to the whole of the religious landscape.
This response is part of the discussion forum 'Catholic Identity and the Revolt of the Netherlands 1520-1635' (Judith Pollmann)
Looking back: Flexible but unbreakable
No full textBiographer Tessel Pollmann rescues from oblivion the engineer who for six decades was one of the most influential people in the Netherlands.Delft University of Technolog
Interne Schwerewelle und turbulente Vermischungsprozesse im Ozean : Beobachtungen und Parametrisierungen
No full textSmall-scale turbulent mixing affects large-scale ocean processes such as the
global overturning circulation but remains unresolved in ocean models. Since
the breaking of internal gravity waves is a major source of this mixing, consistent
parameterizations take internal wave energetics into account. The model
IDEMIX (“Internal Wave Dissipation, Energy and Mixing”) predicts the internal
wave energy, dissipation rates and diapycnal diffusivites based on a
simplification of the spectral radiation balance of the wave field and can be
used as a mixing module in global numerical simulations. In this thesis, it is
evaluated against finestructure estimates of turbulent dissipation rates derived
from Argo float observations. In addition, a novel method to compute internal
gravity wave energy from finescale strain information alone is presented and
applied. IDEMIX well reproduces the magnitude and the large-scale variations
of the Argo-derived dissipation rate and energy level estimates. Deficiencies
arise with respect to the detailed vertical structure or the spatial
extent of mixing hotspots. This points toward the need to improve the forcing
functions in IDEMIX, both by implementing additional physical detail and by
better constraining the processes already included in the model.
As a first step, a new semi-analytical method to describe the internal
wave forcing by the interaction of the barotropic tide with rough bottom topography is presented. It is based on linear theory for variable stratification and finite depth, that is, it computes the energy flux into the different vertical modes for subcritical topography and small tidal excursion. In contrast to earlier semi-analytic approaches, the new one computes for the first time not only the magnitude but also the direction of this energy transfer and gives a positive definite conversion field. Sensitivity studies using both idealized and realistic topography allow the identification of suitable numerical parameter settings and corroborate the accuracy of the method. This motivates the application to the global ocean in order to better account for the geographical distribution of diapycnal mixing induced by low mode internal gravity waves, which can propagate over large distances before breaking. The first results highlight the significant differences of energy flux magnitudes with direction, confirming the relevance of this moredetailed approach for energetically consistent mixing parameterizations in ocean models.Kleinskalige turbulente Vermischung beeinflusst großskalige Ozeanprozesse wie die globale Umwälzzirkulation, wird aber in Ozeanmodellen nicht aufgelöst. Da das Brechen interner Schwerewellen eine wichtige Ursache für diese Vermischung darstellt, basieren konsistente Parametrisierungen auf der Energetik der internen Wellen. Das Modell IDEMIX (Interne-Wellen-Dissipation, -Energie und Vermischung’’) prognostiziert ausgehend von einer vereinfachten Form der spektralen Energiebilanzgleichung die Energie der internen Wellen, deren Dissipationsraten und die diapyknischen Diffusivitäten und kann als Vermischungsmodul in numerischen Simulationen genutzt werden. In dieser Dissertation wird es gegen Feinstrukturabschätzungen der turbulenten Dissipationsraten, die von Argo-float-Beobachtungen stammen, evaluiert. Zusätzlich wird eine neue Methode zur Berechnung der Wellenenergie aus isopyknischer Deformation allein vorgestellt und angewandt. IDEMIX kann die Größenordnung und die großskaligen Variationen der Argo-Dissipationsraten und -energien gut reproduzieren. Schwachstellen sind vor allem in Bezug auf die detaillierte Vertikalstruktur oder die räumliche Ausdehnung von Gebieten hoher Dissipationsraten und Energien zu erkennen. Dies deutet auf die Notwendigkeit, die Antriebsfunktionen in IDEMIX zuverbessen, hin — sowohl durch die Implementierung zusätzlicher physikalischer Details als auch durch die verbesserte Beschreibung von Prozessen, die bereits im Modell enthalten sind. Als ein erster Schritt wird eine neue, semi-analytische Methode vorgestellt, die den Energieeintrag in das interne Wellenfeld durch die Interaktion der barotropen Gezeiten mit dem rauen Meeresboden beschreibt. Sie basiert auf linearer Theorie für variable Schichtung und endliche Tiefe, das heißt, sie berechnet den Energiefluss in die verschiedenen Vertikalmoden für subkritische Topographie und eine kleine Tidenauslenkung. Im Gegensatz zu früheren semi-analytischen Ansätzen bestimmt die neue Methode nicht nur den Betrag, sondern auch die Richtung dieses Energietransfers and errechnet ausschließlich positiv definite Übertragungsraten. Sensitivitätsstudien mit idealisierter und realistischer Topographie dienen zur Festlegung geeigneter numerischer Parameter und bestätigen die Qualität der Methode. Dies motiviert ihre Anwendung auf globalen Skalen um die geographische Verteilung der diapyknischen Vermischung, die durch die kleinen Moden der internen Wellen - jene Wellen, die sich über große Distanzen ausbreiten, bevor sie brechen - hervorgerufen wird, genauer zu beschreiben. Die ersten Resultaten unterstreichen die deutlichen Unterschiede des Energieflusses in die verschiedenen Richtungen und bestätigen damit die Relevanz dieses detaillierteren Ansatzes für energetisch konsistente Vermischungsparametrisierungen in Ozeanmodellen
Resolving the Horizontal Direction of Internal Tide Generation: Global Application for the M2 Tide’s First Mode
No full textBreaking internal tides contribute substantially to small-scale turbulent mixing in the ocean interior and hence to maintaining the large-scale overturning circulation. How much internal tide energy is available for ocean mixing can be estimated by using semianalytical methods based on linear theory. Until recently, a method resolving the horizontal direction of the internal waves generated by conversion of the barotropic tide was lacking. We here present the first global application of such a method to the first vertical mode of the principal lunar semidiurnal internal tide. We also show that the effect of supercritical slopes on the modally decomposed internal tides is different than previously suggested. To deal with this the continental shelf and the shelf slope are masked in the global computation. The global energy conversion obtained agrees roughly with the previous results by Falahat et al. if the mask is applied to their result, which decreases their energy conversion by half. Thus, around half of the energy conversion obtained by their linear calculations occurs at continental slopes and shelves, where linear theory tends to break down. The barotropic-to-baroclinic energy flux at subcritical slopes away from the continental margins is shown to vary substantially with direction depending on the shape and orientation of topographic obstacles and the direction of the local tidal currents. Taking this additional information into account in tidal mixing parameterizations could have important ramifications for vertical mixing and water mass properties in global numerical simulations. </p
Effects of the asymmetry between surface and interior flow on the dynamics of a thermohaline loop
No full textLarge-scale overturning cells in the ocean typically combine an essentially horizontal surface branch and an interior branch below, where the circulation spans both horizontal and vertical scales. The aim of this study is to analyze the impact of this asymmetry between the two branches by “folding” a one-dimensional thermohaline loop, such that its lower part remains vertical while its upper part is folded down into the horizontal plane. It is found that both the transitory response and the distribution of thermohaline properties are modified significantly when the loop is folded. In some cases, velocity oscillations are induced during the spinup that were not seen in the unfolded case. This is because a circular loop allows for compensations between the density torques produced above and below the heat forcing level, while such compensations are not possible in the folded loop because of the horizontal direction of the surface circulation. Furthermore, the dynamical effects associated with nonlinearities of the equation of state are significantly altered by the folding. Cabbeling tends to decelerate the flow in the folded loop, instead of accelerating it as in the circular case, and can also act to dampen velocity oscillations. Thermobaricity also alters the loop circulation, although comparatively less
Het C.O.P.E.-proces
No full textDocument(en) uit de collectie Chemische Procestechnologie.DelftChemTechApplied Science
A Model of Energy and Spectral Shape for the Internal Gravity Wave Field in the Deep Sea: The Parametric IDEMIX Model
No full textThe spectral description of the energy of oceanic internal gravity waves is generally represented by the Garrett–Munk (GM) model, a function with a power-law decrease of spectral energy in wavenumber–frequency space. Besides the slopes of these power laws, the spectrum is expressed as a function of energy and a bandwidth parameter that fixes the range of vertical modes excited in the respective state. Whereas concepts have been developed and agreed upon of what processes feed the wave spectrum and what dissipates energy, there is no explanation of what shapes the spectral distribution, i.e., how the power laws come about and what sets the bandwidth. The present study develops a parametric spectral model of energy and bandwidth from the basic underlying energy balance in terms of forcing, propagation, refraction, spectral transfer, and dissipation. The model is an extension of the IDEMIX (Internal Wave Dissipation, Energy and Mixing) models where bandwidth was taken as a constant parameter. The current version of the model is restricted to single-column mode and the slopes of the spectral power laws are fixed. A coupled system of predictive equations for energy and bandwidth (for up- and downward propagating waves) results. The equations imply that bandwidth relates to energy by a power law with an exponent given by the dynamical parameters. It agrees favorably with energy, bandwidth, and slope data from previously published fits of the GM model to Argo float observations. Numerical solutions of the coupled energy–bandwidth model in stand-alone modus are presented
Evaluating the Global Internal Wave Model IDEMIX Using Finestructure Methods
No full textSmall-scale turbulent mixing affects large-scale ocean processes such as the global overturning circulation
but remains unresolvedin ocean models. Since the breaking of internal gravity waves is a major source of this
mixing, consistent parameterizations take internal wave energetics into account. The model Internal Wave
Dissipation,EnergyandMixing(IDEMIX)predictstheinternalwaveenergy,dissipationrates,anddiapycnal
diffusivities based on a simplification of the spectral radiation balance of the wave field and can be used as a mixing module in global numerical simulations. In this study, it is evaluated against finestructure estimates of turbulent dissipation rates derived from Argo float observations. In addition, a novel method to compute internal gravity wave energy from finescale strain information alone is presented and applied. IDEMIX well reproducesthe magnitudeandthelarge-scalevariations ofthe Argo-derived dissipationrateandenergylevel
estimates. Deficiencies arise with respect to the detailed vertical structure or the spatial extent of mixing hot spots. This points toward the need to improve the forcing functions in IDEMIX, both by implementing
additionalphysicaldetailandbybetterconstrainingtheprocessesalreadyincludedinthemodel.Aprominent
example is the energy transfer from the mesoscale eddies to the internal gravity waves, which is identified as
an essential contributor to turbulent mixing in idealized simulations but needs to be better understood
through the help of numerical, analytical, and observational studies in order to be represented realistically in ocean models
Magic
No full textThis section of The Oxford Guide to the Historical Reception of Augustine explores magic. The author discusses: magic in Aug.'s thought; medieval reception-encyclopedic and legal; medieval reception-theological and philosophical; Renaissance magic and the Protestant Reformation; and modern academic and Max Weber
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