A relation between magnetic field strength and temperature in sunspots

We present Stokes I Zeeman splitting measurements of sunspots using the highly sensitive (g = 3) Fe i line at = 1.5649 m. The splittings are compared with simultaneous intensity measurements in the adjacent continuum. The relation between magnetic field strength and temperature has a characteristic, nonlinear shape in all the spots studied. In the umbra, there is an approximately linear relation between B ² and T _b, consistent with magnetohydrostatic equilibrium in a nearly vertical field. A distinct flattening of the B ² vs T _brelationship in the inner penumbra may be due to changes in the lateral pressure balance as the magnetic field becomes more horizontal; spatially unresolved intensity inhomogeneities may also influence the observed relation.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.     

Stochastic Modeling of Groundwater Extractions over a Data-Sparse Region of Australia

Setting limit on groundwater extractions is important to ensure sustainable groundwater management. Lack of extraction data can affect interpretations of historical pressure changes, predictions of future impacts, accuracy of groundwater model calibration, and identification of sustainable management options. Yet, many groundwater extractions are unmetered. Therefore, there is a need for models that estimate extraction rates and quantify model outputs uncertainties arising due to a lack of data. This paper develops such a model within the Generalized Linear Modeling (GLM) framework, using a case study of stock and domestic (SD) extractions in the Surat Cumulative Management Area, a predominantly cattle farming region in eastern Australia. Various types of extraction observations were used, ranging from metering to analytically-derived estimates. GLMs were developed and applied to estimate the property-level extraction amounts, where observation types were weighted by perceived relative accuracy, and well usage status. The primary variables found to affect property-level extraction rates were: yearly average temperature and rainfall, pasture, property area, and number of active wells; while variables most affecting well usage were well water electrical conductivity, spatial coordinates, and well age. Results were compared with analytical estimates of property-level extraction, illustrating uncertainties and potential biases across 20 hydrogeological units. Spatial patterns of mean extraction rates (and standard deviations) are presented. It is concluded that GLMs are well suited to the problem of extraction rate estimation and uncertainty analysis, and are ideal when model verification is supported by measurement of a random sample of properties.     

Determining hydrologic pathways of streamflow using geochemical tracers in a claypan watershed

Despite the low permeability of claypan soils, groundwater has been heavily contaminated by nitrate in agricultural watersheds dominated by claypan soils. However, it is unclear how nitrate concentrations in groundwater affect stream water quality. In this study, streamflow pathways were investigated using natural geochemical tracers in the 73-km² Goodwater Creek Experimental Watershed in northeastern Missouri. Samples were collected from 2011 to 2017 from stream water (weekly-biweekly), precipitation (event-based), groundwater in 25 wells with screened depths varying from 2 to 16 m (bimonthly–seasonal) and interflow above the claypan in 7 shallow piezometers (weekly–monthly). The results of endmember mixing analysis using major ions indicate that streamflow was dominated by near-surface runoff (59 ± 20%), followed by interflow (25 ± 16%) and groundwater (16 ± 13%). Analysis of endmember distances using the mixing space defined by stream water chemistry suggests that groundwater contributions to streamflow came primarily from the intermediate to deep glacial till aquifer near and below 8 m. Near-surface runoff was persistent and dominant even after isolated precipitation events during a prolonged dry period. It is hypothesised that the alluvial aquifer near stream banks acts as a mixing zone to receive and store various source waters, resulting in persistent delivery of runoff to the stream. Groundwater, even though its contribution was limited, plays a significant role in regulating streamflow NO₃⁻ concentrations. This study significantly improves our understanding of claypan hydrology and will lead to the development of models and decision support tools for implementation of management practices that improve groundwater and stream water quality in restrictive layer watersheds.     

Experimental phase and melting relations of metapelite in the upper mantle: implications for the petrogenesis of intraplate magmas

We performed a series of piston-cylinder experiments on a synthetic pelite starting material over a pressure and temperature range of 3.0–5.0 GPa and 1,100–1,600°C, respectively, to examine the melting behaviour and phase relations of sedimentary rocks at upper mantle conditions. The anhydrous pelite solidus is between 1,150 and 1,200°C at 3.0 GPa and close to 1,250°C at 5.0 GPa, whereas the liquidus is likely to be at 1,600°C or higher at all investigated pressures, giving a large melting interval of over 400°C. The subsolidus paragenesis consists of quartz/coesite, feldspar, garnet, kyanite, rutile, ±clinopyroxene ±apatite. Feldspar, rutile and apatite are rapidly melted out above the solidus, whereas garnet and kyanite are stable to high melt fractions (>70%). Clinopyroxene stability increases with increasing pressure, and quartz/coesite is the sole liquidus phase at all pressures. Feldspars are relatively Na-rich [K/(K + Na) = 0.4–0.5] at 3.0 GPa, but are nearly pure K-feldspar at 5.0 GPa. Clinopyroxenes are jadeite and Ca-eskolaite rich, with jadeite contents increasing with pressure. All supersolidus experiments produced alkaline dacitic melts with relatively constant SiO₂ and Al₂O₃ contents. At 3.0 GPa, initial melting is controlled almost exclusively by feldspar and quartz, giving melts with K₂O/Na₂O ~1. At 4.0 and 5.0 GPa, low-fraction melting is controlled by jadeite-rich clinopyroxene and K-rich feldspar, which leads to compatible behaviour of Na and melts with K₂O/Na₂O ≫ 1. Our results indicate that sedimentary protoliths entrained in upwelling heterogeneous mantle domains may undergo melting at greater depths than mafic lithologies to produce ultrapotassic dacitic melts. Such melts are expected to react with and metasomatise the surrounding peridotite, which may subsequently undergo melting at shallower levels to produce compositionally distinct magma types. This scenario may account for many of the distinctive geochemical characteristics of EM-type ocean island magma suites. Moreover, unmelted or partially melted sedimentary rocks in the mantle may contribute to some seismic discontinuities that have been observed beneath intraplate and island-arc volcanic regions.     

‘Strange changes’: Indigenous perspectives of climate change and adaptation in NE Arnhem Land (Australia)

Despite growing global attention to the development of strategies and policy for climate change adaptation, there has been little allowance for input from Indigenous people. In this study we aimed to improve understanding of factors important in integration of Yolngu perspectives in planning adaptation policy in North East Arnhem Land (Australia). We conducted workshops and in-depth interviews in two ‘communities’ to develop insight into Yolngu peoples’ observations and perspectives on climate change, and their ideas and preferences for adaptation. All participants reported observing changes in their ecological landscape, which they attributed to mining, tourism ‘development’, and climate change. ‘Strange changes’ noticed particularly in the last five years, had caused concern and anxiety among many participants. Despite their concern about ecological changes, participants were primarily worried about other issues affecting their community's general welfare. The results suggest that strategies and policies are needed to strengthen adaptive capacity of communities to mitigate over-arching poverty and well-being issues, as well as respond to changes in climate. Participants believed that major constraints to strengthening adaptive capacity had external origins, at regional, state and federal levels. Examples are poor communication and engagement, top-down institutional processes that allow little Indigenous voice, and lack of recognition of Indigenous culture and practices. Participants’ preferences for strategies to strengthen community adaptive capacity tended to be those that lead towards greater self-sufficiency, independence, empowerment, resilience and close contact with the natural environment. Based on the results, we developed a simple model to highlight main determinants of community vulnerability. A second model highlights components important in facilitating discourse on enhancing community capacity to adapt to climatic and other stressors.     

Hydrologic Sensitivity of Global Rivers to Climate Change

Climate predictions from four state-of-the-art general circulation models (GCMs) were used to assess the hydrologic sensitivity to climate change of nine large, continental river basins (Amazon, Amur, Mackenzie, Mekong, Mississippi, Severnaya Dvina, Xi, Yellow, Yenisei). The four climate models (HCCPR-CM2, HCCPR-CM3, MPI-ECHAM4, and DOE-PCM3) all predicted transient climate response to changing greenhouse gas concentrations, and incorporated modern land surface parameterizations. Model-predicted monthly average precipitation and temperature changes were downscaled to the river basin level using model increments (transient minus control) to adjust for GCM bias. The variable infiltration capacity (VIC) macroscale hydrological model (MHM) was used to calculate the corresponding changes in hydrologic fluxes (especially streamflow and evapotranspiration) and moisture storages. Hydrologic model simulations were performed for decades centered on 2025 and 2045. In addition, a sensitivity study was performed in which temperature and precipitation were increased independently by 2 °C and 10%, respectively, during each of four seasons. All GCMs predict a warming for all nine basins, with the greatest warming predicted to occur during the winter months in the highest latitudes. Precipitation generally increases, but the monthly precipitation signal varies more between the models than does temperature. The largest changes in the hydrological cycle are predicted for the snow-dominated basins of mid to higher latitudes. This results in part from the greater amount of warming predicted for these regions, but more importantly, because of the important role of snow in the water balance. Because the snow pack integrates the effects of climate change over a period of months, the largest changes occur in early to mid spring when snow melt occurs. The climate change responses are somewhat different for the coldest snow dominated basins than for those with more transitional snow regimes. In the coldest basins, the response to warming is an increase of the spring streamflow peak, whereas for the transitional basins spring runoff decreases. Instead, the transitional basins have large increases in winter streamflows. The hydrological response of most tropical and mid-latitude basins to the warmer and somewhat wetter conditions predicted by the GCMs is a reduction in annual streamflow, although again, considerable disagreement exists among the different GCMs. In contrast, for the high-latitude basins increases in annual flow volume are predicted in most cases.     

Finite strain theories and comparisons with seismological data

All the finite strain equations that we are aware of that are worth considering in connection with the interior of the Earth are given, with the assumptions on which they are based and corresponding relationships for incompressibility and its pressure derivatives in terms of density. In several cases, equations which have been presented as new or independent are shown to be particular examples of more general equations that are already familiar. Relationships for deriving finite strain equations from atomic potential functions or vice versa are given and, in particular it is pointed out that the Birch-Murnaghan formulation implies a sum of power law potentials with even powers. All the equations that survive simple plausibility tests are fitted to the lower mantle and outer core data for the PEM earth model. For this purpose the model data are extrapolated to zero temperature, using the Mie-Grüneisen equation to subtract the thermal pressure (at fixed density) and the pressure derivative of this equation to substract the thermal component of incompressibility. Fitting of finite strain equations to such zero temperature data is less ambiguous than fitting raw earth model data and leads immediately to estimates of the low temperature zero pressure parameters of earth materials. On this basis, using the best fitting equations and constraining core temperature to give an extrapolated incompressibilityK ₀=1.6×10¹¹Pa, compatible with a plausible iron alloy, the following numerical data are obtained: Core-mantle boundary temperature 3770 K Zero pressure, zero temperature densities: lower mantle 4190 kg m^–3 outer core (solidified) 7500 kg m^–3 Zero pressure, zero temperature incompressibility of the lower mantle 2.36×10¹¹PaHowever, an inconsistency is apparent betweenP() andK() data, indicating that, even in the PEM model, in which the lower mantle is represented by a single set of parameters, it is not perfectly homogeneous with respect to composition and phase.     

A thermal model of the earth

A thermal model, consistent as far as possible with the parameterised earth model of Dziewonski et al. and with thermodynamic principles and relevant equations of state, is tabulated. This is made more secure by two recent developments, an experimental study of the FeS eutectic to 100 kbar by Usselman and a calculation by Bukowinski which reveals an electronic phase collapse of potassium in the 200–300 kbar range and explains the core heat source. Use is made of the Vashchenko-Zubarev formulation of the Grüneisen ratio, and Lindemann's melting law, both of which have been shown recently to have particular relevance at very high pressures. Values of electronic specific heat and the Grüneisen ratio, which contribute significantly to core properties are calculated from the electron equation of state of Zharkov and Kalinin.