Estimates of effective surface roughness over complex terrain

Turbulence data collected in an area of three-dimensional complex terrain using instruments atteched to the tether cable of a captive balloon together with radiosonde ascents are presented. In addition, data collected using only radiosonde ascents in an area of two-dimensional complex terrain of large slope are also shown. Eddy correlation measurements of the turbulent momentum flux and wind velocity profiles are used to deduce the magnitude of the effective roughness from the drag coefficient and normalised velocity profiles. A relationship connecting the terrain characteristics and the roughness length is compared with the experimental data for both types of terrain plus previous experimental estimates of the roughness length over complex terrain. The formula taken from previous work by Grant and Mason (1990) is found to agree with the data when representing an area of order 100 km².     

Snow days? Snowmaking adaptation and the future of low latitude, high elevation skiing in Arizona, USA

Inter-annual snow reliability is a key short-term concern for Arizona’s high elevation, low latitude ski resorts. Variability is linked to the El Niño Southern Oscillation (ENSO)–warm phase conditions typically portend a good ski season and vice versa. To operate more consistently in the medium-term Arizona’s two largest ski resorts plan to expand snowmaking. Snowmaking is a water and temperature constrained adaptation. One of the two resorts has overcome its water constraint by contracting with a municipality for treated wastewater. To assess the temperature constraint downscaled global coupled climate model temperature projections were compared to technical thresholds for the manufacture of snow at three time steps. In 2030, a period coincident with the lifetime of the investments, snowmaking will likely remain feasible. However, by 2050, temperatures will likely exceed technical thresholds in the shoulder seasons meaning that in years when natural snowfalls are poor the ski season may be curtailed. By 2080, without snowmaking efficiency improvements, warmer temperatures will make snowmaking increasingly more expensive and resort managers may need to plan for a future where operations and snowmaking are shifted to higher elevation, shaded, more snow reliable runs.     

Fractionation of the platinum-group elments and Re during crystallization of basalt in Kilauea Iki Lava Lake, Hawaii

Kilauea Iki lava lake formed during the 1959 summit eruption of Kilauea Volcano, then crystallized and differentiated over a period of 35 years. It offers an opportunity to evaluate the fractionation behavior of trace elements in a uniquely well-documented basaltic system. A suite of 14 core samples recovered from 1967 to 1981 has been analyzed for 5 platinum-group elements (PGE: Ir, Os, Ru, Pt, Pd), plus Re. These samples have MgO ranging from 2.4 to 26.9 wt.%, with temperatures prior to quench ranging from 1140 °C to ambient (110 °C). Five eruption samples were also analyzed.Osmium and Ru concentrations vary by nearly four orders of magnitude (0.0006–1.40 ppb for Os and 0.0006–2.01 ppb for Ru) and are positively correlated with MgO content. These elements behaved compatibly during crystallization, mostly likely being concentrated in trace phases (alloy or sulfide) present in olivine phenocrysts or included chromite. Iridium also correlates positively with MgO, although less strongly than Os and Ru. The somewhat poorer correlation for Ir, compared with Os and Ru, may reflect variable loss of Ir as volatile IrF₆ in some of the most magnesian samples.Rhenium is negatively correlated with MgO, behaving as an incompatible trace element. Its behavior in the lava lake is complicated by apparent volatile loss of Re, as suggested by a decrease in Re concentration with time of quenching for lake samples vs. eruption samples. Platinum and Pd concentrations are negatively, albeit weakly, correlated with MgO, so these elements were modestly incompatible during crystallization of the major silicate phases. Palladium contents peaked before precipitation of immiscible sulfide liquid, however, and decline sharply in the most differentiated samples. In contrast, Pt appears to have been unaffected by sulfide precipitation. Microprobe data confirm that Pd entered the sulfide liquid before Re, and that Pt is not strongly chalcophile in this system. Occasional high Pt values in both eruption and lava lake samples suggest the presence of unevenly distributed, unidentified Pt-rich trace phases in some Kilauea Iki materials.Estimated mineral (olivine + chromite)/melt D values for Os, Ir, Ru and Pt for equilibrium crystallization for samples from ~ 7 to 27 wt.% MgO are 26, 8.2, 19 and 0.55, respectively. These Os, Ir and Ru estimates are somewhat higher than previous estimates for similar systems. If fractional crystallization is instead assumed, D values are much more similar.Results confirm many prior observations in other mafic systems that olivine (together with included phases) has a major effect on absolute and relative abundances of Re and the PGE. The relatively linear correlations between these elements and MgO potentially permit accurate estimation of the concentrations of these elements in the primary melts of comparable systems, especially in instances where the MgO content of the primary melt is well constrained.     

Herschel SPIRE FTS telescope model correction

Emission from the Herschel telescope is the dominant source of radiation for the majority of SPIRE Fourier transform spectrometer (FTS) observations, despite the exceptionally low emissivity of the primary and secondary mirrors. Accurate modelling and removal of the telescope contribution is, therefore, an important and challenging aspect of FTS calibration and data reduction pipeline. A dust-contaminated telescope model with time invariant mirror emissivity was adopted before the Herschel launch. However, measured FTS spectra show a clear evolution of the telescope contribution over the mission and strong need for a correction to the standard telescope model in order to reduce residual background (of up to 7 Jy) in the final data products. Systematic changes in observations of dark sky, taken over the course of the mission, provide a measure of the evolution between observed telescope emission and the telescope model. These dark sky observations have been used to derive a time dependent correction to the telescope emissivity that reduces the systematic error in the continuum of the final FTS spectra to ～0.35 Jy.     

Herschel SPIRE FTS relative spectral response calibration

Herschel/SPIRE Fourier transform spectrometer (FTS) observations contain emission from both the Herschel Telescope and the SPIRE Instrument itself, both of which are typically orders of magnitude greater than the emission from the astronomical source, and must be removed in order to recover the source spectrum. The effects of the Herschel Telescope and the SPIRE Instrument are removed during data reduction using relative spectral response calibration curves and emission models. We present the evolution of the methods used to derive the relative spectral response calibration curves for the SPIRE FTS. The relationship between the calibration curves and the ultimate sensitivity of calibrated SPIRE FTS data is discussed and the results from the derivation methods are compared. These comparisons show that the latest derivation methods result in calibration curves that impart a factor of between 2 and 100 less noise to the overall error budget, which results in calibrated spectra for individual observations whose noise is reduced by a factor of 2–3, with a gain in the overall spectral sensitivity of 23 % and 21 % for the two detector bands, respectively.     

Footpath erosion in the English Lake District

Footpath erosion is a matter of concern in the English Lake District, where recreational pressure on the fells is increasing. Erosion may be expected to result from the interaction of recreational geomorphological and climatic forces with the inherent resistance of vegetation and soil conditions. A broad-scale survey of 485 sites on 25 paths in the Lake District demonstrated the importance of specific variables for footpath erosion. Erosion (measured as path width, extent of bare ground or maximum depth) is found to increase with the square root of the slope angle and the square of the recreation pressure. These two variables also interact with each other, while other factors, such as vegetation type, soil type and topographic position, also influence rate of erosion. A threshold slope angle of 15–17° seems to separate actively eroding from stable slopes.     

Stratigraphy and structural summary of the Cooma Metamorphic Complex

A technique for obtaining age estimates for regolith profiles in Australia, based on the oxygen‐isotope composition of the clay mineral assemblage in a profile, is applied to a variety of regolith profiles and kaolinitic sediments from across Australia. Excluding monsoonal regions in the north of the continent, it is possible to distinguish profiles formed in the Late Mesozoic‐Early Tertiary (δ¹⁸O values between +15 and +17.5%δō) from profiles formed in post‐mid‐Tertiary times (>+17.5%ō). In addition it is concluded that there remain widespread remnants of a deep‐weathered regolith which developed in pre‐Late Mesozoic (Early Cretaceous or Jurassic?) times when Australia was at high latitude. The low δ¹⁸O values associated with clays formed in pre‐Late Mesozoic times (+10 to +15%o) suggest that deep weathering took place in a cool to cold and presumably humid climate, contrary to the traditional belief that deep weathering requires tropical to subtropical temperatures. The formation of deep‐weathered profiles at high latitude in a comparatively cold climate may be linked in part to higher past atmospheric CO₂ levels.     

The structure of a small complexly‐deformed area within Ordovician rocks near Mansfield,Victoria

Two distinct groups of granitoids occur on the eastern side of the Kosciusko Batholith. Those considered to be derivatives of sedimentary source rocks (S‐types) are usually foliated and either contain cordierite or white‐mica secondary after cordierite. The granitoids produced from igneous source material (I‐types) are generally massive and frequently contain hornblende. Geochemical parameters provide the best discriminant between the two groups, I‐types have higher Ca, Al, Na₂O/K₂O, and Fe₂O₃/FeO, and lower Fe, Mg, Sc, V, Cr, Co, Ni, Cu, Zn, Ba, Rb, Th, La, Ce, and Y than S‐types of comparable SiO₂ values.

The differences between the two groups are not the result of differences in the melt‐forming process but reflect differences in the nature of the source material. Thus the geochemical features of the S‐type granitoids are indicative of their source rocks having been through a process of chemical weathering in a sedimentary cycle. Conversely, the I‐type granitoids were derived from fractionated rocks that had not been involved in weathering processes.     

Observations and parametrization of momentum transfer in heterogeneous terrain consisting of regularly spaced obstacles

Tethered balloon data collected over a heterogeneous, semi-rural area of southern England are presented. The terrain within which the observations were taken is dominated by regularly spaced bluff obstacles that form the boundaries to grass fields. The data are compared with previous surface data to assess how representative these fixed-point measurements are of area-averaged values. It is found that there is a vertical height above which the flow approximates to being homogeneous and observations made above it are representative of the area average. The effective roughness length for momentum is then compared with that derived from a model describing the drag partition around isolated obstacles that are either non-porous or porous to the incident flow. It is shown that the method chosen to partition the drag is of the right order to produce reasonable predictions of the effective roughness length for different roughness densities.     

Dust in the core of the metal-rich globular cluster NGC 6356

We report the 3.5σ detection of dust in the core of the metal-rich ([Fe/H] =−0.4) globular cluster NGC 6356. The dust mass in the core is ∼ 4–17 × 10⁻³ M⊙, depending on the dust equilibrium temperature. We rule out sputtering as a grain destruction mechanism in NGC 6356, unless grains are very small (∼30 Å). We also place the upper limit of 6.6 × 10⁻³ on the CO-to-dust ratio in this cluster. This value is significantly smaller than the CO-to-dust ratio in the general Galactic interstellar medium, and in the outflows of evolved stars.