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Doc Marsh R. Boatlanding
No full textDoc Marsh R. Boatlandinghttps://digitalmaine.com/mgs_geologic_field_photos/5441/thumbnail.jp
Marsh, R W, WX17639
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/401600Surname: MARSH. Given Name(s) or Initials: R W. Military Service Number or Last Known Location: WX17639. Missing, Wounded and Prisoner of War Enquiry Card Index Number: 45824.221246
Item: [2016.0049.33893] "Marsh, R W, WX17639
Variability of water masses and circulation in the subtropical North Atlantic
Full text linkObservations of interannual variability in 18 Water (Talley and Raymer 1982) and Gulf Stream transport (Worthington 1977) motivate an ocean model sensitivity study. The North Atlantic circulation is simulated with a three-dimensional isopycnic coordinate GCM. Idealized anomalous buoyancy-forcing fields (associated without breaks of cold, dry continental air over the Gulf Stream/Sargasso Sea region) are constructed. In a series of sensitivity experiments, wintertime buoyancy loss over the Gulf Stream and Sargasso Sea is thus increased to varying degrees, with anomalous ocean-to-atmosphere buoyancy fluxes of up to double climatological values. Under excess buoyancy loss, winter mixed layer depths increase, and a greater volume of model 18 Water is formed. End-of-winter mixed layer density also increases, leading to the formation of a denser variety of 18 Water. The anomalous 18 Water recirculates around the Sargasso Sea as a signal of low potential vorticity, which spreads out and weakens on a decadal timescale. Strengthened horizontal pressure gradients in the vicinity of the anomalous 18 Water drive intensified baroclinic transports at the "immediate" end of winter (in March), after which a full-depth barotropic intensification of the Gulf Stream develops. Strongest intensification occurs in May, when the Gulf Stream barotropic transport is increased locally by up to 10 Sv. The anomalous transports which account for barotropic intensification are confined to deep and abyssal layers of the model. Where the associated anomalous bottom currents traverse isobaths, "extra" bottom pressure torque (BPT) is invoked. Ananomalous BPT term in the barotropic vorticity balance may therefore account for the intensification. Computed from the model fields of density and sea surface height, such a term does appear to produce the extra negative vorticity associated with anticyclogenic intensification. It is concluded that wintertime excess buoyancy loss drives a springtime barotropic response of the subtropical gyre, through BPT, due to "JEBAR" (the Joint Effect of Baroclinicity And Relief). The Gulf Stream intensification decreases after May as lateral eddy mixing weakens anomalous cross-stream pressure gradients. This eddy mixing is parameterized in the model by a layer thickness diffusion velocity, ud, nominally chosen to be 1.0 cm s-1. Further experiments establish the sensitivity of intensification strength to the choice of ud. With ud = 0.1 cm s-1 (weak thickness diffusion), the intensification is increased by ~50%, while, for ud - 10 cm s-1 (strong thickness diffusion), the intensification is roughly halved. These further sensitivity experiments also reveal the varying degrees to which the model subtropical gyre can be dominated by diffusive eddy mixing (Rhines and Young 1982a, 1982b) or adiabatic (nondiffusive) ventilation of the thermocline (Luyten, Pedlosky and Stommel 1983). Recent (1980-97) interannual variability in the formation and recirculation of 18 Water, and other water masses, is deduced from observed surface heat and freshwater fluxes. Interannual variations in the strength of 18 Water renewal (thus deduced) and a wintertime index of the North Atlantic Oscillation (NAO) are found to be strongly anticorrelated (with a correlation coefficient of -0.70, statistically significant at a 99% confidence level). A further sensitivity experiment establishes that anomalous wind forcing, characteristic of a minimum phase in the NAO, does not intensify the GulfStream in the manner of excess cooling. It is concluded that 18 Water is more strongly renewed, with accompanying Gulf Stream intensification, under NAO-minimum buoyancy forcing
Modelling changes in North Atlantic circulation under the NAO-Minimum Wind Forcing of 1877-81
No full textTracing water masses with particle trajectories in an isopycnic-coordinate model of the global ocean
No full textOffline particle trajectories are obtained for a quasi-global isopycnic-coordinate OGCM using an analytical method, adapted for use with online time-integrated isopycnal and diapycnal mass fluxes. The method is highly efficient, allowing the calculation of large ensembles of such trajectories. These ensembles can be used to establish pathways and transformations associated with the global circulation of water masses on timescales which are well in excess of any feasible model integration length. The method is here used to investigate the important, yet poorly observed, transformation of North Atlantic Deep Water (NADW) through slow spreading, upwelling and diapycnal mixing (defined when and where density decreases below a threshold value). A fundamental problem arises through unsteadiness in the thickness of NADW layers (due to various model flaws and/or intrinsic variability). Particles converge on gridboxes where layers inflate during the online time-integration period. Depending on the degree of layer inflation, only a fraction of NADW particles can be diagnosed as transformed at some point along their respective trajectories. However, the unsteadiness of layer thickness decreases during a 50-year spin-up, implying fewer converged trajectories and an increased fraction of transformed NADW. Using trajectories to trace NADW southward across the equatorial Atlantic, with mass fluxes from years 10, 30 and 50 of model spin-up, the transformed percentage (of NADW exported from the North Atlantic) increases from 17–18% (with fluxes from years 10 and 30) to 41% (using year 50 fluxes). In the latter case, about 30% of the NADW upwells south of 30°S after 500–1000 years. Most of the remaining 70% upwells in the South and North Pacific after 1000–2500 years
Parameter estimation in an intermediate complexity earth system model using an ensemble Kalman filter
No full textWe describe the development of an efficient method for parameter estimation and ensemble forecasting in climate modelling. The technique is based on the ensemble Kalman filter and is several orders of magnitude more efficient than many others which have been previously used to address this problem. As well as being theoretically (near-)optimal, the method does not suffer from the 'curse of dimensionality' and can comfortably handle multivariate parameter estimation. We demonstrate the potential of this method in identical twin testing with an intermediate complexity coupled AOGCM. The model's climatology is successfully tuned via the simultaneous estimation of 12 parameters. Several minor modifications arc described
by which the method was adapted to a steady state (temporally averaged) case. The method is relatively simple to implement, and with only O(50) model runs required, we believe that optimal parameter estimation is now accessible even to computationally demanding models
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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