Phytoplankton patch patterns: Seascape anatomy in a turbulent ocean

Marine phytoplankton experience competition, predation, infection and aggregation occurring across distances of micrometres to centimetres. However, the consequences of these interactions influence global processes, such as climate and fisheries productivity. There is a long-standing default assumption that these global processes cannot be traced to plankton distributions and interactions below a few metres because of the homogenising effect of turbulence [Hutchinson, G.E., 1961. The paradox of the plankton. Am. Nat. 95, 137–146.; Siegel, D.A., 1998. Resource competition in a discrete environment: Why are plankton distributions paradoxical? Limnol. Oceanogr. 43, 1133–1146.]. We show that, in active turbulence, phytoplankton patches, on the order of 10 cm, have repeatable asymmetry and regular spacing over distances of centimetres to tens of metres. The regularity and hierarchical nature of the patches in mixed ocean water means that phytoplankton are distributed in a dynamic, but definite seascape topography, where groups of patches coalesce between intermittent turbulent eddies. These patches may link large scale processes and microscale interactions, acting as fundamental components of marine ecosystems that influence grazing efficiency, taxonomic diversity, and the initiation of aggregation and subsequent carbon flux.     

Characterization of incidents on an urban arterial road

The early warning of incidents on urban arterial roads in a congested city can reduce delay, accidents and pollutant emission. Freeway incident detection systems implemented in recent years may not be suitable for arterial incidents. Arterial incident detection is more difficult. The traffic flow on an arterial road is not conserved from the upstream end of a road link to the downstream end because urban traffic does turn in and out of side‐streets, car‐parks and local residences. Roadside friction such as kerbside parking and shopping traffic also tends to create apparent incidents which are in fact frequent and normal events. This paper develops a definition for an arterial incident and describes a case study on an arterial road in Melbourne, Australia. The study shows that detectors upstream of an incident are more useful for incident detection than downstream detectors. It also identifies occupancy and speed as the appropriate parameters to characterise and detect arterial incidents.     

Calibration of large-scale transport planning models: a structured approach

Transportation - Traditionally, transport planning model systems are estimated and calibrated in an unstructured way, which does not allow for interactions among included parameters to be...     

Variation in cost overruns of transportation projects: an econometric meta-regression analysis of studies reported in the literature

Transportation - This paper uses an econometric meta-regression analysis framework to examine how the mean percentage cost overruns (MPCOs) of transportation projects reported in the literature...     

Amtrak,the attempt to renew U.S. rail service

The decline of railway passenger train patronage and the deterioration of service in the United States have led the U.S. Government to assume control over the operation of trains via a quasi‐federal corporation called “Amtrak,” but some basic causes of the decline remain and new problems will arise as a result of this action.

Two results of the neglect to assess external costs against the various transport modes is an unbalance in favor of those with the higher external costs and the continued, seemingly fundamental, unprofitability of railway passenger service, which exists even for equipment that operates at capacity!

Some way of collecting external costs will have to be found, and the problems created by the new intrusion of the U.S. Government into transport will have to be faced.     

A novel method for estimating vertical eddy diffusivities using diurnal signals with application to western Long Island Sound

We present an approach that allows the estimation of vertical eddy diffusivity coefficients from buoy measurements made at two or more depths. By measuring the attenuation and phase lag of a scalar signal generated periodically at the surface as it propagates downwards, the vertical eddy diffusivity coefficients can be calculated as K_v = ωΔz²/2ln²(α₂/α₁), where α₂/α₁ is the ratio of the real amplitudes at frequency ω at the two depths separated by Δz = z₂ − z₁; as K_V = ωΔz²/2φ², where φ is the phase lag at the frequency ω; or as K_v = iωΔz²/ln²(U₂/U₁), where U₂/U₁ is the ratio of the complex signal amplitudes at the two depths. The method requires that horizontal fluxes be small at the ω frequency and that the signal-to-noise ratios at the two depths allow the determination of the amplitude and phase of ω.Application of this method to summertime 2004 western Long Island Sound oxygen and temperature buoy measurements at two depths provides a time-series of two-day average vertical eddy diffusivity estimates. Using these eddy diffusivities in conjunction with measured vertical concentration gradients, we obtain a time-series of vertical transport rates for oxygen and heat and estimate mean downward fluxes for June and July as 150–260 mMol m^− 2 day^− 1 and 100–400 W m^− 2 respectively. These estimates are of a similar magnitude to sub-pycnocline O₂ and heat demands of 240 ± 200 mMol m^− 2 day^− 1 and 180 ± 60 W m^− 2 that we infer from simple budgets, implying that vertical transport is significant to both budgets.The eddy coefficients obtained from the independent O₂ and temperature measurements have a 68% correlation, and the O₂ flux estimates show a correlation of 41% to measured rates of change in bottom dissolved oxygen levels. Our results indicate that extended time-series of eddy diffusivity coefficients can be obtained from in situ buoy measurements and the method shows promise as a way to constrain the vertical transport variability in budgets of dissolved materials in estuaries.     

Advection schemes for shelf sea models

Numerical models of shelf seas must handle sharp gradients in thermoclines and fronts, and at the edges of patches of passive tracer, often in the presence of strong tidal currents, without introducing excessive numerical diffusion or spurious oscillations. In a sigma coordinate model there is an additional problem, since then purely horizontal motion over a sloping sea bed may introduce strong numerical diffusion in the vertical, which can artificially erode thermoclines.In this paper, two advection schemes applicable to shelf sea models are examined. They are based on TVD (Total Variation Diminishing) and PPM (Piecewise Parabolic Method) techniques. They are demonstrated to give satisfactory performance for tracer advection in one, two and three dimensions. They are both monotonic, and the PPM scheme has particularly low numerical diffusion. In two and three dimensions directional splitting is used, which is handled by following advection with each horizontal velocity component by adjustment of the sigma levels in each water column using the same advection scheme. The artificial vertical diffusion is then small, particularly with PPM.The two schemes are also compared in a three-dimensional model of a cylindrical eddy of relatively fresh water, released from rest in an open sea region. Here, both salinity and momentum are advected. Laboratory experiments show that after an initial period of adjustment the eddy should become unstable, with a growth of cyclonic-anticyclonic eddy pairs. This is reproduced in the model, with the PPM scheme again producing sharper results than the TVD scheme.Integrated second moment calculations are used to compare the schemes. These demonstrate the lower numerical diffusion of the PPM scheme. This advantage is achieved at the cost of greater computing time.     

Aspects of family and kinship in a North Carolina coastal community: a comparative study

The almost total absence of social-science data on North Carolina coastal fishing communities has provoked this preliminary study of the role played by family and kinship ties among fishermen and boat builders in such a community, with a view to developing new fisheries management strategies from an assessment of the social and economic impacts of those which already exist.