A photochemical model of the martian atmosphere

The factors governing the amounts of CO, O2, and O3 in the martian atmosphere are investigated using a minimally constrained, one-dimensional photochemical model. We find that the incorporation of temperature-dependent CO2 absorption cross sections leads to an enhancement in the water photolysis rate, increasing the abundance of OH radicals to the point where the model CO abundance is smaller than observed. Good agreement between models and observations of CO, O2, O3, and the escape flux of atomic hydrogen can be achieved, using only gas-phase chemistry, by varying the recommended rate constants for the reactions CO + OH and OH + HO2 within their specified uncertainties. Similar revisions have been suggested to resolve discrepancies between models and observations of the terrestrial mesosphere. The oxygen escape flux plays a key role in the oxygen budget on Mars; as inferred from the observed atomic hydrogen escape, it is much larger than recent calculations of the exospheric escape rate for oxygen. Weathering of the surface may account for the imbalance. Quantification of the escape rates of oxygen and hydrogen from Mars is a worthwhile objective for an upcoming martian upper atmospheric mission. We also consider the possibility that HOx radicals may be catalytically destroyed on dust grains suspended in the atmosphere. Good agreement with the observed CO mixing ratio can be achieved via this mechanism, but the resulting ozone column is much higher than the observed quantity. We feel that there is no need at this time to invoke heterogeneous processes to reconcile models and observations.     

Effects of heavy metals on the survival ofDiacypris compacta (Herbst) (Ostracoda) from the Coorong,South Australia

The hypermarine southern Coorong is threatened by proposals to drain relatively fresh surface water and groundwater from adjacent agricultural areas into the Coorong. These influent waters carry moderate loads of heavy metals. Acute toxicity of heavy metals toDiacypris compacta, an abundant ostracod in the Coorong, was measured in the laboratory at 18°C in a static system using Coorong water (pH 7.8 salinity 50 ppt). At 4 days (96 h) the mean values of LC₅₀ for copper, zinc, lead and, cadmium respectively were 0.8, 2.1, 3.1 and 4.3 mg L^–1, and at 8 days the respective mean LC₅₀ s were 0.4, 0.7, 2.2 and 1.1 mgL^–1. The effect of two or three metals on mortality was additive in some cases and synergistic in other cases, but generally less than additive. However, in all cases mortality was greater in the presence of two or three metals than in the presence of a single metal. According to ANZECC (1992) guidelines, maximum acceptable concentrations of heavy metals should be no higher than 0.01 x the lowest LC₅₀ value. Using the lowest LC₅₀ values forDiacypris compacta obtained at 8 days, maximum acceptable concentrations in the Coorong would be 4, 5, 9 and 22 gL^–1 for copper, zinc, cadmium and lead respectively, the values for zinc and copper failling below those recommended by ANZECC (1992) for marine waters. Reported concentrations of copper and zinc in surface water and groundwater in areas adjacent to the Coorong sometimes exceed these values, hence drainage of these waters into the Coorong represents a significant hazard to the Coorong biota.     

Resistive ballooning line-tied boundary conditions

Ideal and resistive ballooning modes are investigated for different ratios of a two-layer stratified density region representing a model for the photospheric/coronal boundary. Construction of the ballooning equations using a WKB approach is justified by comparison between the values of the growth rate obtained using Hain-Lüst and ballooning equations together with a WKB integral relation. Different values of the density ratio, radius, and resistivity are considered. Sausage-type and kink-type instabilities are found. One of these, depending on the value of r remained unstable for large density ratios. The other instability tended to marginal stability as the density ratio was increased, and allowed parallel and perpendicular flows across the boundary. This is contrary to the predictions of both the rigid-wall and flow-through conditions.     

Water vapor adsorption by sodium montmorillonite at −5°C

A large amount of interest has recently been expressed pertaining to the quantity of physically adsorbed water by the Martian regolith. Thermodynamic calculations based on experimentally determined adsorption and desorption isotherms and extrapolated to subzero temperatures indicate that physical adsorption of more than one or two monomolecular layers is highly unlikely under Martian conditions. Any additional water would find ice to be the state of lowest energy and therefore the most stable form. To test the validity of the thermodynamic calculations we have measured adsorption and desorption isotherms of sodium montmorillonite at ?5°C. To a first approximation it was found to be valid.     

Pre-flare association of magnetic fields and millimeter-wave radio emission

Observations of radio emission at 3.3 mm wavelength associated with magnetic fields in active regions are reported. Results of more than 200 regions during the years 1967–1968 show a strong correlation between peak enhanced millimeter emission, total flux of the longitudinal component of photospheric magnetic fields and the number of flares produced during transit of active regions. For magnetic flux greater than 10²¹ maxwells flares will occur and for flux of 10²³ maxwells the sum of the H flare importance numbers is about 40. The peak millimeter enhancement increases with magnetic flux for regions which subsequently flared. Estimates of the magnetic energy available and the correlation with flare production indicate that the photospheric fields and probably chromospheric currents are responsible for the observed pre-flare heating and provide the energy of flares.This work was supported in part by NASA Contract No. NAS2-7868 and in part by Company funds of The Aerospace Corporation.     

The formation of saturn's satellites and rings,as influenced by saturn's contraction history

We have used Pollack et al.'s 1976 calculations of the quasi-equilibrium contraction of Saturn to study the influence of the planet's early high luminosity on the formation of its satellites and rings. Assuming that the condensation of ices ceased at the same time within Jupiter's and Saturn's primordial nebulae, and using limits for the time of cessation derived for Jupiter's system by Pollack and Reynolds (1974) and Cameron and Pollack (1975), we arrive at the following tentative conclusions. Titan is the innermost satellite at whose position a methane-containing ice could condense, a result consistent with the presence of methane in this satellite's atmosphere. Water ice may have been able to condense at the position of all the satellites, a result consistent with the occurrence of low-density satellites close to Saturn. The systematic decrease in the mass of Saturn's regular satellites with decreasing distance from Saturn may have been caused partially by the larger time intervals for the closer satellites between the start of contraction and the first condensation of ices at their positions and between the start of contraction and the time at which Saturn's radius became less than a satellite's orbital radius. Ammonia ices, principally NH₄SH, were able to condense at the positions of all but the innermost satellites.Water ice may bave been able to condense in the region of the rings close to the end of the condensation period. We speculate that the rings are unique to Saturn because on the one hand, temperatures within Jupiter's Roche limit never became cool enough for ice particles to form before the end of the condensation period and on the other hand, ice particles formed only very early within Uranus' and Neptune's Roche limits, and were eliminated by gas drag effects that caused them to spiral into the planet before the gas of these planets' nebula was eliminated. Gas drag would also have eliminated any rocky particles initially present inside the Roche limit.We also derive an independent estimate of several million years for the time between the start of the quasi-equilibrium contraction of Saturn and the cessation of condensation. This estimate is based on the density and mass characteristics of Saturn's satellites. Using this value rather than the one found for Jupiter's satellites, we find that the above conclusions about the rings and the condensation of methane-and ammonia-containing ices remain valid.     

Application of the QUILF thermobarometer to the peralkaline trachytes and pantellerites of the Eburru volcanic complex, East African Rift, Kenya

The Quaternary Eburru volcanic complex in the south-central Kenya Rift consists of pantelleritic trachytes and pantellerites. The phenocryst assemblage in the trachytes is sanidine + fayalite + ferrohedenbergite + aenigmatite ± quartz ± ilmenite ± magnetite ± pyrrhotite ± pyrite. In the pantellerites, the assemblage is sanidine + quartz + ferrohedenbergite + fayalite + aenigmatite + ferrorichterite + pyrrhotite ± apatite, although fayalite, ferrohedenbergite and ilmenite are absent from more evolved rocks (e.g. with SiO₂ > 71%). QUILF temperature calculations for the trachytes range from 709 to 793 °C and for the pantellerites 668–708 °C, the latter temperatures being among the lowest recorded for peralkaline silicic magmas. The QUILF thermobarometer demonstrates that the Eburru magmas crystallized at relatively low oxidation states (ΔFMQ + 0.5 to − 1.6) for both trachytes and pantellerites. The trachytes and pantellerites evolved along separate liquid lines of descent, the trachytes possibly deriving from a more mafic parent by fractional crystallization and the pantellerites from extreme fractionation of comenditic magmas.     

Net Energy Payback and CO2 Emissions from Three Midwestern Wind Farms: An Update

This paper updates a life-cycle net energy analysis and carbon dioxide emissions analysis of three Midwestern utility-scale wind systems. Both the Energy Payback Ratio (EPR) and CO₂ analysis results provide useful data for policy discussions regarding an efficient and low-carbon energy mix. The EPR is the amount of electrical energy produced for the lifetime of the power plant divided by the total amount of energy required to procure and transport the materials, build, operate, and decommission the power plants. The CO₂ analysis for each power plant was calculated from the life-cycle energy input data. A previous study also analyzed coal and nuclear fission power plants. At the time of that study, two of the three wind systems had less than a full year of generation data to project the life-cycle energy production. This study updates the analysis of three wind systems with an additional four to eight years of operating data. The EPR for the utility-scale wind systems ranges from a low of 11 for a two-turbine system in Wisconsin to 28 for a 143-turbine system in southwestern Minnesota. The EPR is 11 for coal, 25 for fission with gas centrifuge enriched uranium and 7 for gaseous diffusion enriched uranium. The normalized CO₂ emissions, in tonnes of CO₂ per GW_eh, ranges from 14 to 33 for the wind systems, 974 for coal, and 10 and 34 for nuclear fission using gas centrifuge and gaseous diffusion enriched uranium, respectively.     

Melt loss and the preservation of granulite facies mineral assemblages

The loss of a metamorphic fluid via the partitioning of H₂O into silicate melt at higher metamorphic grade implies that, in the absence of open system behaviour of melt, the amount of H₂O contained within rocks remains constant at temperatures above the solidus. Thus, granulite facies rocks, composed of predominantly anhydrous minerals and a hydrous silicate melt should undergo considerable retrogression to hydrous upper amphibolite facies assemblages on cooling as the melt crystallizes and releases its H₂O. The common occurrence of weakly retrogressed granulite facies assemblages is consistent with substantial melt loss from the majority of granulite facies rocks. Phase diagram modelling of the effects of melt loss in hypothetical aluminous and subaluminous metapelitic compositions shows that the amount of melt that has to be removed from a rock to preserve a granulite facies assemblage varies markedly with rock composition, the number of partial melt loss events and the P–T conditions at which melt loss occurs. In an aluminous metapelite, the removal of nearly all of the melt at temperatures above the breakdown of biotite is required for the preservation of the peak mineral assemblage. In contrast, the proportion of melt loss required to preserve peak assemblages in a subaluminous metapelite is close to half that required for the aluminous metapelite. Thus, if a given proportion of melt is removed from a sequence of metapelitic granulites of varying composition, the degree of preservation of the peak metamorphic assemblage may vary widely.