The separation point of a midlatitude jet from the western boundary in ocean numerical models depends upon both the governing equations and the vertical coordinate used. Systematic differences in the ...point of separation between level and layer models are shown. In level models, the separation usually occurs poleward of the zero wind-stress curl line, whereas, in layer models, it usually occurs equatorward. These differences are caused by two aspects of the numerical implementation. First, the wind forcing is usually assumed to act as a body force over the upper layer or level in the models, and this corresponds to a different physical assumption. Second, the free-slip boundary condition is imposed as zero vorticity in both models. This is an inconsistency because vorticity is not the same quantity when the governing equations are formulated in physical (level model) and isopycnal (layer model) coordinates. The effects on separation of these numerical implementation differences are illustrated using analytical solutions of linear models and numerical solutions of several nonlinear models.
The seasonal heat transport mechanisms important in the Pacific equatorial upwelling zone are investigated using the primitive equation, reduced gravity model developed by Gent and Cane. Mechanisms ...of meridional heat transport are shown and discussed with respect to the heat budget of a box about the equator containing the upwelling. There is a horizontal cell in which warm water enters the upwelling box in the west in strong equatorward currents located near the western boundary, which feed the eastward flowing undercurrent. To compensate, water leaves the section as a colder and weaker poleward thermocline flow in the eastern basin. The meridional-vertical cell comprises additional equatorward geostrophically balanced inflow in the upper thermocline, which is compensated by the warmer poleward outflow by Ekman divergence in the surface layer.
Tracer budgets in the warm water sphere MCWILLIAMS, JAMES C.; DANABASOGLU, GOKHAN; GENT, PETER R.
Tellus. Series A, Dynamic meteorology and oceanography,
January 1996, 1996, 1996-01-00, 19960101, Letnik:
48, Številka:
1
Journal Article
Recenzirano
ABSTRACT
In global equilibrium numerical solutions for the oceanic general circulation, we examine the time‐mean budgets for the tracers potential temperature and salinity integrated over volumes ...bounded by interior surfaces of constant tracer values and lying within the warm water sphere. In this domain, the budgets have surface fluxes primarily of one sign that must be balanced by mesoscale and microscale fluxes through its lower boundary, because advection makes a zero integral contribution. The mesoscale fluxes are represented by the isopycnally orientated, quasiadiabatic parameterization of Gent and McWilliams and contribute little to the integral budgets where isopycnals are nearly tangent to the volume boundary. The microscale fluxes occur with a small vertical diffusivity (κv = O(10−5) m2 s−1) in the predominantly stably stratified warm water sphere, yet they are shown to be sufficient to provide the primary balance against surface forcing in all ocean basins and over a wide range of tracer values. This is especially true for potential temperature because of the close alignment of isotherms and isopycnals. For salinity, however, the mesoscale isopycnal diffusion also contributes significantly to the budget. The budgets are dominated by the surface and interior fluxes from the time‐mean circulation, although there are also modest contributions from the rectification of the seasonal cycle. These results are in contrast to previous analyses that concluded that much larger vertical diffusivities are required for budget balance. We do not attempt to fully resolve the relatively smaller role of vertical diffusion in other budget volumes outside the warm water sphere.
On Kelvin waves in balance models ALLEN, J. S; GENT, P. R; HOLM, D. D
Journal of physical oceanography,
09/1997, Letnik:
27, Številka:
9
Journal Article
Recenzirano
Odprti dostop
The f-plane linear shallow-water equations support coastal Kelvin waves. These waves propagate along the coast and have zero velocity normal to the coast. It is shown that the balance equations also ...support coastal Kelvin waves, but these waves differ depending upon the boundary conditions imposed. Three different boundary conditions and resulting Kelvin wave approximations are examined. It is shown that one set of boundary conditions gives balance-model Kelvin waves that are closer to those of the shallow-water equations than the other two boundary conditions.
Luyten and Roemmich have shown a strong semiannual signal in zonal velocity in the upper, western part of the equatorial Indian Ocean. Their observations are modelled by assuming that they are ...directly forced by the observed semiannual component of zonal wind stress, which is relatively large in the equatorial Indian Ocean. The model is linear, periodic, has linear damping, uses the long-wave approximation, and can be solved analytically. A good comparison with the observations is obtained for the phase of the oscillation across the array. The predicted magnitude is somewhat smaller than in the observations. The model sensitivity to friction and the spatial distribution of the wind stress is explored. Some additional model simplifications are discussed, but it is concluded that they all detract substantially from the comparison. The main conclusion is that the observations can be explained as a directly forced response to the semiannual component of the near-equatorial zonal winds.
Action to reduce anthropogenic impact on the environment and species within it will be most effective when targeted towards activities that have the greatest impact on biodiversity. To do this ...effectively we need to better understand the relative importance of different activities and how they drive changes in species' populations. Here, we present a novel, flexible framework that reviews evidence for the relative importance of these drivers of change and uses it to explain recent alterations in species' populations. We review drivers of change across four hundred species sampled from a broad range of taxonomic groups in the UK. We found that species' population change (~1970-2012) has been most strongly impacted by intensive management of agricultural land and by climatic change. The impact of the former was primarily deleterious, whereas the impact of climatic change to date has been more mixed. Findings were similar across the three major taxonomic groups assessed (insects, vascular plants and vertebrates). In general, the way a habitat was managed had a greater impact than changes in its extent, which accords with the relatively small changes in the areas occupied by different habitats during our study period, compared to substantial changes in habitat management. Of the drivers classified as conservation measures, low-intensity management of agricultural land and habitat creation had the greatest impact. Our framework could be used to assess the relative importance of drivers at a range of scales to better inform our policy and management decisions. Furthermore, by scoring the quality of evidence, this framework helps us identify research gaps and needs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The linear, normal mode instability of barotropic circular vortices with zero circulation is examined in the f-plane quasigeostrophic equations. Equivalents of Rayleigh's and Fjortoft's criteria and ...the semicircle theorem for parallel shear flow are given, and the energy equation shows the instability to be barotropic. A new result is that the fastest growing perturbation is often an internal instability, having a finite vertical scale, but may also be an external instability, having no vertical structure. For parallel shear flow the fastest growing perturbation is always an external instability; this is Squire's theorem. Whether the fastest growing perturbation is internal or external depends upon the profile: for mean flow streamfunction profiles which monotonically decrease with radius, the instability is internal for less steep profiles with a broad velocity extremum and external for steep profiles with a narrow velocity extremum. Finite amplitude, numerical model calculations show that this linear instability analysis is not valid very far into the finite amplitude range, and that a barotropic vortex, whose fastest growing perturbation is internal, is vertically fragmented by the instability.
Synthetic antimicrobial and antibiofilm peptide (SAAP-148) commits significant antimicrobial activities against antimicrobial resistant (AMR) planktonic bacteria and biofilms. However, SAAP-148 is ...limited by its low selectivity index, i.e., ratio between cytotoxicity and antimicrobial activity, as well as its bioavailability at infection sites. We hypothesized that formulation of SAAP-148 in PLGA nanoparticles (SAAP-148 NPs) improves the selectivity index due to the sustained local release of the peptide. The aim of this study was to investigate the physical and functional characteristics of SAAP-148 NPs and to compare the selectivity index of the formulated peptide with that of the peptide in solution. SAAP-148 NPs displayed favorable physiochemical properties size = 94.1 ± 23 nm, polydispersity index (PDI) = 0.08 ± 0.1, surface charge = 1.65 ± 0.1 mV, and encapsulation efficiency (EE) = 86.7 ± 0.3% and sustained release of peptide for up to 21 days in PBS at 37 °C. The antibacterial and cytotoxicity studies showed that the selectivity index for SAAP-148 NPs was drastically increased, by 10-fold, regarding AMR
and 20-fold regarding AMR
after 4 h. Interestingly, the antibiofilm activity of SAAP-148 NPs against AMR
and
gradually increased overtime, suggesting a dose-effect relationship based on the peptide's in vitro release profile. Using 3D human skin equivalents (HSEs), dual drug SAAP-148 NPs and the novel antibiotic halicin NPs provided a stronger antibacterial response against planktonic and cell-associated bacteria than SAAP-148 NPs but not halicin NPs after 24 h. Confocal laser scanning microscopy revealed the presence of SAAP-148 NPs on the top layers of the skin models in close proximity to AMR
at 24 h. Overall, SAAP-148 NPs present a promising yet challenging approach for further development as treatment against bacterial infections.
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