An indirect mechanism for the production of O(1S) in the aurora

Recent laboratory measurements of the deactivation rate constants for O(¹S) have suggested that the dominant production mechanism for the green line in the nightglow is a two-step process. A similar mechanism involving energy transfer from an excited state of molecular oxygen is considered as a potential source of the OI (5577 Å) emission in the aurora. It is shown that the mechanism, $\text{O}{}_2\text{+ e → O}{}_2{}^1\text{+ e O}{}_2{}^1\text{+ O → O}{}_2\text{+ O(}{}^1\text{S}\text{)}$, is consistent with auroral observations; the intermediate excited state has been tentatively identified as the O₂(c¹∑^?_u) state. For the proposed energy transfer mechanism to be the primary source of the auroral green line, the peak electron impact cross-section for O₂¹ production must be approximately 2 × 10^?17 cm².     

A measurement of the O2 ultra-violet nightglow emission

New measurements of the Herzberg I emission height profile in the night airglow are reported and indicate a peak emission height near 96 km in agreement with previous measurements. Using an atomic oxygen concentration profile determined from the oxygen green line profile measured on the same rocket it is concluded that the O₂(A³Σ_u⁺) state is not excited in the direct three body recombination of atomic oxygen. It is suggested that the excitation mechanism is a two step process, similar to the Barth mechanism for the atomic oxygen green lineand that the excited intermediate state is C³Δ_u.     

The altitude dependence of the O2(A3Σu+) vibrational distribution in the terrestrial nightglow

A simple vibrational relaxation model which reproduces the observed altitude integrated vibrational distribution of the Herzberg I bands in the nightglow is used to derive the altitude profiles of the individual vibrational levels at 1 km intervals in the 85–115 km height range. The possible errors associated with using rocket-borne photometer measurements of a limited number of bands in the O₂(A³Σ_u⁺?X³Σ_g^?) system to infer the total Herzberg I emission profile are assessed.     

Flow Characteristics of Cemented Paste Backfill

Cemented paste backfill (CPB) is primarily used for backfilling underground voids at George Fisher Mine (Mount Isa, Australia). The objective of this paper is to summarise the geotechnical characterisation of the tailings and the rheological properties of the CPB as determined from a laboratory testing program undertaken at James Cook University. Two binders were examined [a General Purpose cement and a slag blend cement] over a range of dosages from 0 to 6% and CPB mix solids content in the range of 72–78%. The slump tests were carried out using the standard cone (ASTM C 143) used for concrete and a cylinder with 110 mm (diameter) × 110 mm (height), whereas the yield stress was measured using a shear vane (Brookfield vane spindle V-73). The index characteristics of the tailings including the grain size distribution, liquid limit, plastic limit, specific gravity were determined as per ASTM standards. This paper will then discuss the interrelationships among the solid content, slump, saturated density and the yield stress of the CPB. It is shown that there is strong correlation between the two different slump test devices used in this study. The smaller cylindrical device appears to have good potential for slurries like mine tailings or dredged mud that have high water content for slump test. There is also strong inter-relationship among solid content, slump, yield stress, and bulk density. Increasing the solid content increases the bulk density and yield stress, but reduces the slump. While there is hardly any difference between the two binder types used in this study in terms of flow parameters, namely the yield stress and slump, the binder dosage has an effect. At any specific solid content, higher binder dosages lead to a drop in the slump and increase in the yield stress. The difference is more pronounced in dense slurries. It is also strongly believed that the trends and relationships developed in this study may be valuable for the other mining operations using CPB.     

An operational framework for communicating flood warnings to indigenous farmers in southern Nigeria: a systems thinking analysis

GeoJournal - In March 2012, the Nigerian meteorological agency forecasted massive flooding for parts of the country, with the displacement of large parts of the population as a consequence. Delta...     

On I(5577 Å) and I (7620 Å) auroral emissions and atomic oxygen densities

A model of auroral electron deposition processes has been developed using Monte Carlo techniques to simulate electron transport and energy loss. The computed differential electron flux and pitch angle were compared with in situ auroral observations to provide a check on the accuracy of the model. As part of the energy loss process, a tally was kept of electronic excitation and ionization of the important atomic and molecular states. The optical emission rates from these excited states were computed and compared with auroral observations of (3914 Å), (5577 Å), (7620 Å) and (N₂VK). In particular, the roles played by energy transfer from N₂(A³⁺_u) and by other processes in the excitation of O(¹S) and O₂(b¹⁺_g) were investigated in detail. It is concluded that the N₂(A³⁺_u) mechanism is dominant for the production of OI(5577 Å) in the peak emission region of normal aurora, although the production efficiency is much smaller than the measured laboratory value; above 150 km electron impact on atomic oxygen is dominant. Atomic oxygen densities in the range of 0.75±0.25 MSIS-86 [O] were derived from the optical comparisons for auroral latitudes in mid-winter for various levels of solar and magnetic activity.     

A measurement of the O2(b1Σg+−X3Σg−) atmospheric band and the OI(1S) green line in the nightglow

Simultaneous measurements of the nightglow profiles of the O₂(b¹Σ_g⁺?X³Σ_g^?) A-band, the atomic oxygen green line and the OH (8?3) Meinel band are presented. The altitude profiles are used to determine both the excitation mechanisms for the oxygen emissions and the atomic oxygen altitude distribution. It is shown that the measurements are consistent with a green line excitation through the Barth mechanism and that the molecular oxygen emission is excited through oxygen recombination and the reaction between OH¹ and atomic oxygen. The derived atomic oxygen concentrations,6.2 × 10¹¹cm^?3at 98km, are consistent with the Jacchia (1971) model.     

The excitation of the infrared atmospheric oxygen bands in the nightglow

Simultaneous observations of the nightgiow emission profiles of $\text{O}{}_2\text{(}{}^1\text{Δ)}$ and the OH Meinel bands have been used to show that the excitation mechanism for $\text{O}{}_2\text{(}{}^1\text{Δ)}$ in the night-time is through the reaction between OH¹ and atomic oxygen and the recombination of atomic oxygen. These reactions, and the proposed rate constants, have been used to derive the atomic oxygen profile appropriate to the observations. It is suggested that the atomic oxygen profile may exhibit significant structure near the mesopause at high latitude. It is also suggested that the extent of this structure may be influenced by transport effects related to stratospheric warming events.     

On the variability of I(7620 Å)/I(5577 Å) in low altitude aurora

An auroral electron excitation model, combined with simple equilibrium neutral and ion chemistry models, is used to investigate the optical emission processes and height profiles of I(5577 Å) and I(7620 Å) in the 90 to 100 km altitude region. It is shown that the apparent discrepancies between ground-based and rocket-borne auroral observations of the I(7620 Å)/I(5577 Å) ratio are due to the extreme height variation of this intensity ratio in the 90 to 100 km region.