Dependence of ground-based Pc5 ULF wave power on F10.7 solar radio flux and solar cycle phase

Utilising fifteen (1990–2005) years of ground-based magnetometer data from four magnetometer stations, we characterise the statistical dependence of the Pc5 ULF wave power spectra on variations in F10.7 solar radio flux and on solar cycle phase. We show that the median Pc5 ULF wave power spectra can be characterised as a power-law with a localised Gaussian centred at a specific frequency superimposed on the power-law spectrum. Further, we demonstrate that the location of the Gaussian in frequency systematically varies with both solar cycle phase and F10.7 and is more pronounced during high-speed solar wind intervals. We postulate that the localised power spectrum enhancement (or Gaussian) is a manifestation of the local eigenfrequency of field line resonances in the Earth's magnetosphere and that the variation in the location of the Gaussian occurs as a result of increased ionospheric outflow during periods of enhanced F10.7 and active solar activity.     

Climate impact of transportation A model comparison

Transportation contributes to a significant and rising share of global energy use and GHG emissions. Therefore modeling future travel demand, its fuel use, and resulting CO₂ emission is highly relevant for climate change mitigation. In this study we compare the baseline projections for global service demand (passenger-kilometers, ton-kilometers), fuel use, and CO₂ emissions of five different global transport models using harmonized input assumptions on income and population. For four models we also evaluate the impact of a carbon tax. All models project a steep increase in service demand over the century. Technology change is important for limiting energy consumption and CO₂ emissions, the study also shows that in order to stabilise or even decrease emissions radical changes would be required. While all models project liquid fossil fuels dominating up to 2050, they differ regarding the use of alternative fuels (natural gas, hydrogen, biofuels, and electricity), because of different fuel price projections. The carbon tax of 200 USD/tCO₂ in 2050 stabilizes or reverses global emission growth in all models. Besides common findings many differences in the model assumptions and projections indicate room for further understanding long-term trends and uncertainty in future transport systems.     

Hydrogen Eos at Megabar Pressures and the Search for Jupiter’s Core

The interior structure of Jupiter serves as a benchmark for an entire astrophysical class of liquid–metallic hydrogen-rich objects with masses ranging from ~0.1M _J to ~80M _J (1M _J = Jupiter mass = 1.9e30 g), comprising hydrogen-rich giant planets (mass < 13M _J) and brown dwarfs (mass > 13M _J but ~ < 80M _J), the so-called substellar objects (SSOs). Formation of giant planets may involve nucleated collapse of nebular gas onto a solid, dense core of mass ~0.04M _J rather than a stellar-like gravitational instability. Thus, detection of a primordial core in Jupiter is a prime objective for understanding the mode of origin of extrasolar giant planets and other SSOs. A basic method for core detection makes use of direct modeling of Jupiter’s external gravitational potential terms in response to rotational and tidal perturbations, and is highly sensitive to the thermodynamics of hydrogen at multi-megabar pressures. The present-day core masses of Jupiter and Saturn may be larger than their primordial core masses due to sedimentation of elements heavier than hydrogen. We show that there is a significant contribution of such sedimented mass to Saturn’s core mass. The sedimentation contribution to Jupiter’s core mass will be smaller and could be zero.     

A review of the Nimbus-7 ERB solar dataset

Fourteen years (November 16, 1978 through January 24, 1993) of Nimbus-7 total solar irradiance measurements have been made. The measured mean annual solar energy just outside of the Earth's atmosphere was about 0.1% (1.4 W/m²) higher in the peak years of 1979 (cycle 21) and 1991 (cycle 22) than in the quiet Sun years of 1985/86. Comparison with shorter, independent solar measurement sets and with empirical models qualitatively confirms the Nimbus-7 results. But these comparisons also raise questions of detail for future studies: in which years did the peaks actually occur and just how accurate are the models and the measurements?     

Active galactic nuclei jet mass loading and truncation by stellar winds

Active galactic nuclei can produce extremely powerful jets. While tightly collimated, the scale of these jets and the stellar density at galactic centres implies that there will be many jet/star interactions, which can mass load the jet through stellar winds. Previous work employed modest wind mass outflow rates, but this does not apply when mass loading is provided by a small number of high mass-loss stars. We construct a framework for jet mass loading by stellar winds for a broader spectrum of wind mass-loss rates than has previously been considered. Given the observed stellar mass distributions in galactic centres, we find that even highly efficient (0.1 Eddington luminosity) jets from supermassive black holes of masses M _BH≲ 10⁴ M_⊙ are rapidly mass loaded and quenched by stellar winds. For  10⁴ M_⊙ < M _BH < 10⁸ M_⊙  , the quenching length of highly efficient jets is independent of the jet's mechanical luminosity. Stellar wind mass loading is unable to quench efficient jets from more massive engines, but can account for the observed truncation of the inefficient M87 jet, and implies a baryon-dominated composition on scales ≳2 kpc therein even if the jet is initially pair plasma dominated.     

Computation of Jupiter interior models from gravitational inversion theory

A method for deriving a planetary interior model which exactly satisfies a set of N gravitational constraints is implemented. For Jupiter, recent spacecraft measurements provide the mass, radius at a standard pressure level, rotation law, multipole moments of the internal mass distribution, and constraints on the internal composition and temperature distribution. By appropriate iterations, interior models are found which exactly satisfy these constraints. The models are assumed to have constant chemical composition and constant specific entropy in the hydrogenic envelope. The derived pressure-density relation in the outer envelope depends sensitively on the observational uncertainty in the mass multipole moment J₄. Models are not forced to fit the more indirectly derived constraints, which are instead used as consistency checks. For a helium mass fraction in the envelope (Y) equal to 0.20, the inferred pressure at a mass density ≈ 0.2 g/cm³ is about a factor of 2 higher than would be indicated by experimental hydrogen shock compression data in the relevant pressure range of 10⁵ to 10⁶ bar. The inferred pressure distribution is in much better agreement with the shock data for a nominal Y = 0.30 ± 0.05. This value of Y is interpreted in terms of an enhancement in the envelope, by a factor of order 5 over solar abundance, of species primarily consisting of CH₄, NH₃, and possibly H₂O. The same method is applied to Saturn, but existing uncertainties in Saturn's gravitational parameters are still too large to allow useful conclusions about the composition of its envelope.     

Characterizing the phosphorus forms extracted from soil by the Mehlich III soil test

Phosphorus (P) can limit crop production in many soils, and soil testing is used to guide fertilizer recommendations. The Mehlich III (M3) soil test is widely used in North America, followed by colorimetric analysis for P, or by inductively coupled plasma-based spectrometry (ICP) for P and cations. However, differences have been observed in M3 P concentrations measured by these methods. Using ³¹P nuclear magnetic resonance (P-NMR) and mass spectrometry (MS), we characterized P forms in M3 extracts. In addition to the orthophosphate that would be detected during colorimetric analysis, several organic P forms were present in M3 extracts that would be unreactive colorimetrically but measured by ICP (molybdate unreactive P, MUP). Extraction of these P forms by M3 was confirmed by P-NMR and MS in NaOH-ethylenediaminetetraacetic acid extracts of whole soils and residues after M3 extraction. The most abundant P form in M3 extracts was myo-inositol hexaphosphate (myo-IHP, phytate), a compound that may not contribute to plant-available P if tightly sorbed in soil. Concentrations of myo-IHP and other organic P forms varied among soils, and even among treatment plots on the same soil. Extraction of myo-IHP in M3 appeared to be linked to cations, with substantially more myo-IHP extracted from soils fertilized with alum-treated poultry litter than untreated litter. These results suggest that ICP analysis may substantially over-estimate plant-available P in samples with high MUP concentrations, but there is no way at present to determine MUP concentrations without analysis by both colorimetry and ICP. This study also tested procedures that will improve future soil P-NMR studies, such as treatment of acid extracts, and demonstrated that techniques such as P-NMR and MS are complimentary, each yielding additional information that analysis by a single technique may not provide.

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Late Holocene environmental change in Celestun Lagoon,Yucatan, Mexico

Journal of Paleolimnology - Epikarst estuary response to hydroclimate change remains poorly understood, despite the well-studied link between climate and karst groundwater aquifers. The influence...     

Geomorphological characterisation and interpretation of a mid-latitude glacier-like form: Hellas Planitia, Mars

We describe and interpret the surface terrain types associated with a widely-reported ∼4 km long, mid-latitude martian viscous flow feature (VFF). The feature is located in the southern hemisphere, on the poleward-facing rim of a ∼60 km-diameter crater in eastern Hellas Planitia. High Resolution Imaging Science Experiment (HiRISE) images, analysed in both 2D and 3D, reveal that the upper margin of the feature is bounded by steep (∼30°) headwalls, typically some tens of metres high, that are formed from unconsolidated material and characterised by a series of slope-parallel linear incisions. Below these incised headwalls, the feature flows at a general angle of ∼10° from a broad upper basin to a confined lower tongue that is bounded by a nested sequence of elongate raised ridges. These characteristics are typical of several VFFs in the region and are strikingly similar to moraine-bounded valley glaciers on Earth, and we sub-classify this feature as a ‘glacier-like form’ (GLF)¹. The GLF comprises five distinctive surface terrain types that contrast sharply with surface characteristics outside its bounding moraines. Four of these terrains (scaly terrain, polygonized terrain, linear terrain and mound-and-tail terrain) are located within the GLF’s innermost bounding moraine, while the fifth (rectilinear-ridge terrain) is located between its frontal moraines. These terrains are mapped, characterised and associated with possible mechanisms of formation to draw inferences about the GLF’s glaciology and glacial history. This analysis suggests that the GLF reached its maximal extent in the geologically-recent past, and that it may have been partially wet-based at that time. Subsequent to this phase, the GLF experienced an extended period of general recession that has been punctuated by several episodes of still-stand or advance. Currently, the GLF’s basin appears to be composed of a lower zone that is dominated by an exposed former glacier bed and an upper zone that may still contain a now-degraded and dust-mantled viscous mass, similar to many partially-glacierized basins on Earth.