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.     

Interference filter spectral imaging of twilight O+(2P-2D) emission

A spectral imager specifically designed to measure the O⁺(²P-²D) emission in the thermosphere during twilight has been constructed and tested in Toronto (43.8°N, 79.3°W), and found to show promise for long-term and campaign-mode operations. A modification of the mesopause oxygen rotational temperature imager (MORTI), it consists basically of a narrow-band interference filter (0.14 nm bandwidth) to separate wavelengths as a function of off-axis angle, a lens to focus the spectrum into a series of concentric rings, and a focal plane array (CCD) to record the spectral images in digital form. The instrument was built with two fields of view, one for the zenith and one for 20° above the horizon, movable to track the azimuth of the Sun, in order to provide appropriate data for inversion. Data gathered during June 1991 provided measurements of the column-integrated emission rate with a precision of about 3%. An atomic oxygen profile was deduced that showed good agreement with that predicted by the MSIS-90 model atmosphere. Geomagnetically induced variations of the O⁺ lines, calcium spectra resulting from meteor showers, and OH nightglow were also observed.     

Diamondiferous lithospheric roots along the western margin of the Kalahari Craton—the peridotitic inclusion suite in diamonds from Orapa and Jwaneng

The Orapa and Jwaneng kimberlites are located along the western margin of the Kalahari Craton and the prevalence of eclogitic over peridotitic diamonds in both mines has recently been linked to lower P-wave velocities in the deep mantle lithosphere (relative to the bulk of the craton) to suggest a diamond formation event prompted by mid-Proterozoic growth and modification of preexisting Archean lithosphere (Shirey et al. 2002). Here we study peridotitic diamonds from both mines, with an emphasis on the style of metasomatic source enrichment, to evaluate their relationship with this major eclogitic diamond formation event. In their major element chemistry, the peridotitic inclusions compare well with a world-wide database but reveal differences to diamond sources located in the interior of the Western Terrane of the Kaapvaal block, where the classical mines in the Kimberley region are located. The most striking difference is the relative paucity of low-Ca (<2 wt% CaO in garnet) harzburgites and a low ratio of harzburgitic to lherzolitic garnets (2:1). This suggests that lithospheric mantle accreted to the rim of the Zimbabwe and Kaapvaal blocks was overall chemically less depleted. Alternatively, this more fertile signature may be assigned to stronger metasomatic re-enrichment but the trace element signature of garnet inclusions is not in favor of strong enrichment in major elements. For both mines the majority of lherzolitic and harzburgitic garnet inclusions are characterized by moderately sinusoidal REE_N patterns and low Ti, Zr and Y contents, indicative of a metasomatic agent with very high LREE/HREE and low HFSE. This is consistent with metasomatism by a CHO-fluid or, as modeled by Burgess and Harte (2003), a highly fractionated, low-volume silicate melt from the MORB-source. In both cases, changes in the major element chemistry of the affected rocks will be limited. In a few garnets from Orapa preferential MREE enrichment is observed, suggesting that the percolating fluid/melt fractionated a LREE-phyllic phase (such as crichtonite). The overall moderate degree of metasomatism reflected by the inclusion chemistry is in stark contrast to lithospheric sections for Orapa and Jwaneng based on mantle xenocrysts and xenoliths, revealing extensive mantle metasomatism (Griffin et al. 2003). This suggests that the formation of peridotitic diamonds predates the intensive modification of the subcratonic lithosphere during Proterozoic rifting and compression, implying that diamonds may survive major tectonothermal events.Editorial responsibility: J. Hoefs     

Lower thermospheric nitric oxide concentrations derived from WINDII observations of the green nightglow continuum at 553.1 nm

Vertical profiles of nitric oxide in the altitude range 90 to 105 km are derived from 553 nm nightglow continuum measurements made with the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS). The profiles are derived under the assumption that the continuum emission is due entirely to the NO+O air afterglow reaction. Vertical profiles of the atomic oxygen density, which are required to determine the nitric oxide concentrations, are derived from coordinated WINDII measurements of the atomic oxygen OI 557.7 nm nightglow emission. Data coverage for local solar times ranging from 20 h to 04 h, and latitudes ranging from 42°S to 42°N, is achieved by zonally averaging and binning data obtained on 18 nights during a two-month period extending from mid-November 1992 until mid-January 1993. The derived nitric oxide concentrations are significantly smaller than those obtained from rocket measurements of the airglow continuum but they do compare well with model expectations and nitric oxide densities measured using the resonance fluorescence technique on the Solar Mesosphere Explorer satellite. The near-global coverage of the WINDII observations and the similarities to the nitric oxide global morphology established from other satellite measurements strongly suggests that the NO+O reaction is the major source of the continuum near 553 nm and that there is no compelling reason to invoke additional sources of continuum emission in this immediate spectral region.     

ETON 6: A rocket measurement of the O2 Infrared Atmospheric (0-0) band in the nightglow

Co-ordinated rocket measurements of the O₂(a¹Δ_g−X³Σ_g⁻) Infrared Atmospheric (0-0) band emission profile and the atomic oxygen densities in an undisturbed night-time atmosphere are used to investigate the processes responsible for the excitation of O₂(a¹Δ_g) in the terrestrial nightglow. It is shown that three-body recombination of atomic oxygen, and subsequent energy transfer processes, can explain only part of the observed emission profile and that at least two other sources of O₂(a¹Δ_g) emission must exist. One of these additional sources, responsible for most of the emission observed below 90km, is identified as arising from the night-time residual of the very large dayglow ¹Δ_g population. The other additional source is required to explain most of the emission observed above 95km. The processes responsible for this high altitude component cannot be identified but the vertical distribution of the required source function strongly resembles the profile of the atomic oxygen density squared and suggests that a two-body radiative recombination process may be involved. However, the measured zenith emission rates can also be explained without the high altitude source of O₂(a¹Δ_g) if optical emission at 1.27 μm was induced by the rocket as it penetrated the nightglow layer.     

The O(1S) dayglow emission as observed by the WIND imaging interferometer on the UARS

Volume emission rate profiles of the O(¹D-¹S) 5577 Å dayglow measured by the WIND imaging interferometer on the Upper Atmosphere Research Satellite are analyzed to examine the O(¹S) excitation mechanisms in the sunlit lower thermosphere and upper mesosphere. The observed emission profiles are compared with theoretical profiles calculated using a model which takes into account all of the known daytime sources of O(¹S). These include photoelectron impact on atomic oxygen, dissociative recombination of O⁺₂, photodissociation of molecular oxygen, energy transfer from metastable N₂(A³⁺_u) and three body recombination of atomic oxygen. Throughout most of the thermosphere the measured and modelled emission rates are in reasonably good agreement, given the limitations of the model, but in the region below 100 km, where the oxygen atom recombination source is likely to dominate, the measured emission rates are considerably larger than those modelled using the MSIS-90 oxygen atom densities. This discrepancy is discussed in terms of possible inadequacies in the MSIS-90 model atmosphere and/or additional sources of O(¹S) at low altitude.     

Brown trout (Salmo trutta) removal by rotenone alters zooplankton and phytoplankton community composition in a shallow mesotrophic reservoir

Brown trout (Salmo trutta) are known to have effects on multiple trophic levels in New Zealand streams, but their impacts on lower trophic levels are less well understood within lentic systems. We examined the effects of brown trout removal using rotenone on zooplankton and phytoplankton community composition in the Upper Karori Reservoir, New Zealand. Significant shifts were observed in zooplankton and phytoplankton composition following removal of brown trout from the reservoir. Shifts in zooplankton community composition did not occur immediately following trout removal (February), but instead followed the likely timing of galaxiid spawning (July). The removal of brown trout likely resulted in reduced predation pressure on galaxiids. A major change occurred in the zooplankton community with the dominance shifting from larger crustaceans to smaller rotifers, indicating an increased predation pressure from the larval native galaxiid. A delayed response in zooplankton community composition change indicates rotenone was not the direct cause of this. A major shift in phytoplankton community composition occurred immediately following trout removal. This was not consistent with the trophic cascade hypothesis of reduced grazing pressure from larger zooplankton due to increased galaxiid predation as a result of brown trout removal.     

A comment on proposed mechanisms for the excitation of O(1S) in the aurora

A recent assessment by Rees (1984) of the contribution made to the excitation of O(¹S) in the aurora by the reaction of N₂(A³Σ⁺) with O(³P) is re-examined. It is demonstrated that the contribution attributed to this reaction may have been seriously under-estimated and it is shown that the results of recent laboratory investigations do not preclude this reaction as a major source of O(¹s) in the aurora.