Summer thermal structure of lake Ontario off Toronto: Cooling the big city

Abstract

It has been proposed that large savings in electrical energy are possible if cool, deep water from Lake Ontario is used, as an alternative to electrically operated chillers, to provide the cooling requirements of large buildings in down‐town Toronto. In order to estimate the capital expenditure involved, it is necessary to determine how deep (and how far offshore) the cold water intake must be placed to obtain a reliable supply of cool water throughout the air‐conditioning season. Temperature profile data, collected during ship surveys over the past twenty years in Lake Ontario off Toronto, plus time‐series data from a 21‐level thermistor array installed on the 100‐m contour near the site of the proposed intake during the summer of 1980, have been used to answer this specific question. The two sets are examined to determine the relative importance of thermal variability for inter‐annual, seasonal, and shorter time‐scales. Intake design turns out to be an important consideration for the air‐conditioning scheme. Unless azimuthal swirling velocities are restrained at the intake, drawdown of warmer thermocline water into the intake may occur.     

Line-tied magnetic reconnection

We present two-dimensional numerical simulations of magnetic reconnection in a configuration relevant to two-ribbon solar flares. The calculations extend those of Forbes and Priest (1982a, b, 1983) and some puzzling aspects of their results are clarified. In particular, the roles of magnetic diffusion, of the tearing mode and of turbulence are individually examined. We stress the important part played by boundary conditions in determining the evolution of the initial current sheet and suggest that in future the evolution of the entire overlying magnetic arcade be modelled as well as the current sheet that is created below the rising arcade. Tearing at very high magnetic Reynolds numbers is likely to develop into an impulsive bursty regime of reconnection after a time which depends on the initial level of turbulence.     

Wave-particle interactions in a magnetic neutral sheet

The effect of an electrostatic wave on the motion of particles in a magnetic neutral sheet is studied. The first-order perturbation of the distribution function is conveniently obtained by a method in which the changes in the zero-order constants of the motion are calculated. Simple analytic approximation is possible in certain regions of velocity space, but it is shown that in general numerical calculation is required. Some sample numerical results are presented and the conditions for waveparticle resonance discussed.     

Inference and analysis across spatial supports in the big data era: Uncertain point observations and geographic contexts

The ways in which geographic information are produced have expanded rapidly over recent decades. These advances have provided new opportunities for geographical information science and spatial analysis—allowing the tools and theories to be expanded to new domain areas and providing the impetus for theory and methodological development. In this light, old problems of inference and analysis are rediscovered and need to be reinterpreted, and new ones are made apparent. This article describes a new typology of geographical analysis problems that relates to uncertainties in the relationship between individual‐level data, represented as point features, and the geographic context(s) that they are associated with. We describe how uncertainty in context linkage (uncertain geographic context problem) is also related to, but distinct from, uncertainty in point‐event locations (uncertain point observation problem) and how these issues can impact spatial analysis. A case study analysis of a geosocial dataset demonstrates how alternative conclusions can result from failure to account for these sources of uncertainty. Sources of point observation uncertainties common in many forms of user‐generated and big spatial data are outlined and methods for dealing with them are reviewed and discussed.     

Estimates of recharge in two arid basin aquifers: a model of spatially variable net infiltration and its implications (Red Light Draw and Eagle Flats, Texas, USA)

Methods of estimating recharge in arid basin aquifers (such as the 1 % rule, Maxey-Eakin method, storm-runoff infiltration and others) overlook the potential contribution of direct recharge on the basin floors. In the Trans-Pecos region of west Texas, USA, this has resulted in potential recharge and solute flux to basin aquifers being ignored. Observed trends in groundwater nitrate (NO₃ ^?) concentrations and the presence of young (<70 years old) water in the basins indicate that recharge is occurring through the basin floors. A spatially variable net infiltration model (INFIL 3.0.1) was used to estimate the volume and spatial distribution of potential recharge to two basins: Red Light Draw and Eagle Flats. The INFIL model provides insight into the mechanisms by which recharge and solute flux occurs in arid basin systems. This method demonstrated that recharge is widespread; it is not limited to the mountainous areas and mountain-front recharge mechanisms, and up to 15 % of total potential recharge in these basins occurs across widespread areas of the basin floors. Models such as this should improve scientific understanding and sustainable management of arid basin aquifers in Texas and elsewhere.     

Calving retreat and proglacial lake growth at Hooker Glacier,Southern Alps,New Zealand

Hooker Glacier in the central Southern Alps of New Zealand has undergone significant downwasting and recession (～2.14 km) during the last two centuries. High retreat rates (51 m a^?1 1986–2001, 43 m a^?1 2001–2011) have produced a large (1.22 km²) proglacial lake. We present a retreat scenario for Hooker Glacier. A retreat scenario predicts that the glacier terminus will stabilise >3 km up‐valley of the current lake outlet after 2028 when ice velocity equals calving rate.     

Natural attenuation of septic system nitrogen by anammox

On-site disposal of sewage in septic systems can lead to groundwater plumes with NO(3)(-)-N concentrations exceeding the common drinking water limit of 10 mg/L. Currently, denitrification is considered as the principal natural attenuation process. However, at a large seasonal-use septic system in Ontario (256 campsites), a suboxic zone exists where nitrogen removal of up to 80% occurs including removal of NH(4)(+)-N. This zone has both NO(3)(-)-N and NH(4)(+)-N at >5 mg/L each. In the distal NH(4)(+)-rich zone, NH(4)(+)-N concentrations (8.1 ± 8.0 mg/L) are lower than in the proximal zone (48 ± 36 mg/L) and NH(4)(+)-N is isotopically enriched (concentration-weighted mean δ(15)N of +15.7‰) compared to the proximal zone (+7.8‰). Furthermore, δ(15)N-NH(4)(+) isotopic enrichment increases with depth in the distal zone, which is opposite to what would result if nitrification along the water table zone was the mechanism causing NH(4)(+) depletion. Bacterial community composition was assessed with molecular (DNA-based) analysis and demonstrated that groundwater bacterial populations were predominantly composed of bacteria from two Candidatus genera of the Planctomycetales (Brocadia and Jettenia). Together, these data provide strong evidence that anaerobic ammonium oxidation (anammox) plays an important role in nitrogen attenuation at this site.     

Planktonic stages of the teleost family carapidae in eastern New Zealand waters

The occurrence of planktonic carapid eggs in Otago waters, of young stages of Echiodon rendahli off Castlepoint, and the possible presence of unrecorded members of the family Carapidae in New Zealand waters is discussed. Young E. rendahli possess a long spine which originates dorsally to a distinctive suspended gut.     

The two species of sprat in New Zealand waters (Sprattus antipodum and S. muelleri)

Two broadly sympatric species of sprat are shown to inhabit New Zealand waters, the more slender Sprattus antipodum (Hector, 1872) and the more common and deeper‐bodied S. muelleri (Klunzinger, 1872). Overlap in most morphometric and meristic characters had earlier led to their synonymy, but recent protein analysis suggested otherwise. This is now confirmed by distinct differences in shape and dentition of the basihyal plate, vertebral numbers, scale sculpture, and fresh colour. The five known species of Sprattus are keyed and the genus diagnosed and discussed.