The effects of density gradients on the convective amplification of upper hybrid waves in the magnetosphere

Intense (? 10 mVm^?1) electrostatic plasma waves near the upper hybrid frequency have been observed between ± 50° magnetic latitude during spacecraft plasmapause crossings. We present wave growth rate and three-dimensional convective amplification calculations which suggest how intense upper hybrid (IUH) events can occur over such a wide range of latitudes. The effects of wave refraction are shown to be crucial to the proper calculation of convective amplification.We first calculate upper hybrid wave growth for an IUH event at 10° MLAT during which a complete electron distribution function with a loss cone feature was measured simultaneously with the waves. We show that a parallel density gradient may be necessary to account for the observed amplification. Without such a density gradient, the dipole magnetic field gradient would quickly refract the wave vector component parallel to the local field lines out of the unstable region in wave vector space. Upon mapping the distribution function observed at 10° MLAT to other latitudes by conserving the electrons' magnetic moments, we then find that the mapped distribution could produce large amplification at higher latitudes only if there is an appropriate parallel density gradient. At the equator, the long magnetic field gradient scale length enables large amplitudes to be attained without a density gradient.The results of our UH ray tracing analysis are related to theories and observations of magnetospheric continuum radiation.     

The shape of the diffuse cosmic X-ray spectrum

Recent work by Dyer and Morfill has shown that satellite measurements of the diffuse cosmic X-ray spectrum made with crystal scintillators may include errors due to radioactive spallation products formed in the detector by inner belt and cosmic ray protons.

An estimate is made of the magnitude of this source of background for the various experimental situations and it is shown that apparent features at 40 keV and 1 MeV are likely to be due to radioactive decays in the instruments. A review is made of experiments covering the range 1 keV-100 MeV in order to ascertain whether a single exponent spectrum is capable of fitting the experimental results. The astrophysical implications of such a spectrum are briefly considered.

Suggestions are made for the location and correction for background of future experiments.

     

The optical performance of the PILOT instrument from ground end-to-end tests

The Polarized Instrument for Long-wavelength Observation of the Tenuous interstellar medium (PILOT) is a balloon-borne astronomy experiment designed to study the linear polarization of thermal dust emission in two photometric bands centred at wavelengths 240 μm (1.2 THz) and 550 μm (545 GHz), with an angular resolution of a few arcminutes. Several end-to-end tests of the instrument were performed on the ground between 2012 and 2014, in order to prepare for the first scientific flight of the experiment that took place in September 2015 from Timmins, Ontario, Canada. This paper presents the results of those tests, focussing on an evaluation of the instrument’s optical performance. We quantify image quality across the extent of the focal plane, and describe the tests that we conducted to determine the focal plane geometry, the optimal focus position, and sources of internal straylight. We present estimates of the detector response, obtained using an internal calibration source, and estimates of the background intensity and background polarization.     

Universal lateral distribution of energy deposit in air showers and its application to shower reconstruction

The light intensity distribution in a shower image and its implications to the primary energy reconstructed by the fluorescence technique are studied. Based on detailed CORSIKA energy deposit simulations, a universal analytical formula is derived for the lateral distribution of light in the shower image and a correction factor is obtained to account for the fraction of shower light falling into outlying pixels in the detector. The expected light profiles and the corresponding correction of the primary shower energy are illustrated for several typical event geometries. This correction of the shower energy can exceed 10%, depending on shower geometry.     

Sediment lithology and stable isotope composition of organic matter in a core from a cirque in the Krkonoše Mountains,Czech Republic

This study presents detailed lithostratigraphy and stable carbon and nitrogen isotopic variations in a 520-cm-long sediment core from a cirque basin in the Labsky důl Valley, Krkonoše Mountains, Czech Republic. Detailed study of the core reveals five major periods of sedimentation during the last 7600 years: silt and sand deposition during ~7.6–5.1 ka cal BP, Sphagnum peat accumulation during ~5.1–4.0 ka cal BP, sandy silt and sand during ~4.0–2.8 ka cal BP, raised peat bog during ~2.8–2.0 ka cal BP (Sphagnum peat), and sedimentation of sandy silt since ~2.0 ka cal BP. The δ¹³C values of the organic matter in the core vary in the range typical for C3 plants, from −24.35 to −27.68‰, whereas the δ¹⁵N values vary from −2.65 to +4.35‰. Core sections having ash contents ≥70% have δ¹⁵N > 1‰ and δ¹³C < −26‰, whereas those having ≤70% ash content have δ¹⁵N < 1‰ and δ¹³C > −26‰. Strong linear correlations are observed between δ¹³C and δ¹⁵N values as well as between C:N ratios and δ¹⁵N values in the horizons with ash content >10%, primarily for sand and silt horizons. On the other hand, poor correlations between δ¹³C and C:N ratio, as well as δ¹⁵N and C:N ratio, were observed in Sphagnum peat layers (45–125 and 185–265 cm). We conclude that the primary stable isotope variations are not preserved in the layers where significant correlation between δ¹⁵N and C:N ratio is observed. The relatively small δ¹³C variation in the uppermost Sphagnum peat layer suggests stable temperature during ~2.8–2.0 ka cal BP.     

Simulated watershed scale impacts of corn stover removal for biofuel on hydrology and water quality

Ethanol from corn stover is expected to play an important role in achieving the Energy Independence and Security Act 2007 target of 136.25 billion liters (36 billion gallons) of biofuel by 2022. The 2010 USDA biofuel strategic report estimates that 16.3 billion liters (4.3 billion gallons) of biofuel from crop residues such as corn stover and straw is possible. Corn stover is expected to provide the majority of the estimated biofuel from crop residues, especially from the Midwestern US Corn Belt. A major concern related to removing corn stover is potential negative hydrologic and water quality impacts. The overall goal of this study was to estimate the watershed scale environmental impacts of corn stover removal in an agricultural watershed in the Midwest US. Soil and Water Assessment Tool was used to simulate the impacts associated with three corn stover removal rates (38%, 52% and 70%). The stream flow, nitrate and mineral phosphorus loading were reduced, and sediment and organic nitrogen loading were increased at the watershed outlet with all three stover removal scenarios. The stream flow was reduced by 1.4%, 2.0% and 2.7% from the baseline scenario (no stover removed) at 38%, 52% and 70% stover removal rates, respectively. The sediment loading increased by 19.7%, 22.5% and 29.0%, organic nitrogen increased by 0.8%, 2.0% and 5.5%, mineral phosphorus decreased by 11.7%, 15.5% and 21.0%, and nitrate decreased by 2.0%, 3.2% and 5.3% from the baseline scenario at the watershed outlet with 38%, 52% and 70% stover removal rates, respectively. The model results also indicate that the watershed response to stover removal is sensitive to watershed characteristics and management inputs, such as, slope and amount of fertilizer applied. Copyright © 2011 John Wiley & Sons, Ltd.     

Spatially distributed long‐term hydrologic simulation using a continuous SCS CN method‐based hybrid hydrologic model

A continuous Soil Conservation Service (SCS) curve number (CN) method that considers time‐varied SCS CN values was developed based on the original SCS CN method with a revised soil moisture accounting approach to estimate run‐off depth for long‐term discontinuous storm events. The method was applied to spatially distributed long‐term hydrologic simulation of rainfall‐run‐off flow with an underlying assumption for its spatial variability using a geographic information systems‐based spatially distributed Clark's unit hydrograph method (Distributed‐Clark; hybrid hydrologic model), which is a simple few parameter run‐off routing method for input of spatiotemporally varied run‐off depth, incorporating conditional unit hydrograph adoption for different run‐off precipitation depth‐based direct run‐off flow convolution. Case studies of spatially distributed long‐term (total of 6 years) hydrologic simulation for four river basins using daily NEXRAD quantitative precipitation estimations demonstrate overall performances of Nash–Sutcliffe efficiency (E_NS) 0.62, coefficient of determination (R²) 0.64, and percent bias 0.33% in direct run‐off and E_NS 0.71, R² 0.72, and percent bias 0.15% in total streamflow for model result comparison against observed streamflow. These results show better fit (improvement in E_NS of 42.0% and R² of 33.3% for total streamflow) than the same model using spatially averaged gauged rainfall. Incorporation of logic for conditional initial abstraction in a continuous SCS CN method, which can accommodate initial run‐off loss amounts based on previous rainfall, slightly enhances model simulation performance; both E_NS and R² increased by 1.4% for total streamflow in a 4‐year calibration period. A continuous SCS CN method‐based hybrid hydrologic model presented in this study is, therefore, potentially significant to improved implementation of long‐term hydrologic applications for spatially distributed rainfall‐run‐off generation and routing, as a relatively simple hydrologic modelling approach for the use of more reliable gridded types of quantitative precipitation estimations.     

Quaternary soil chronosequences on terraces of the Susquehanna river, Pennsylvania

Susquehanna River terraces are used to establish time lines along a 150 km reach of the river, from the Lower Piedmont to the edge of the Appalachian Plateau. This is achieved by generating soil chronosequences at two locations — Marietta, PA, in the Lower Piedmont, and Muncy, PA, near the glacial border on the boundary between the Valley and Ridge province and the Appalachian Plateau. These sites preserve the most complete record of fluvial incision on the Susquehanna River with flights of seven Quaternary terraces ranging in elevation from 3 m to 51 m above the modern river.Soil characteristics used to develop the soil chronosequences include complexity of horizonization, thickness of B horizon, clay content of B horizon, soil color, CBD extractable Fe, Al, and Mn, total extractable Fe, and clay mineralogy. Terrace age constraints are based on soil development, correlation to regional glacial stratigraphy, correlation to dated fluvial and glaciofluvial deposits, and by paleomagnetic analysis of sediments. Terrace ages at the Muncy site range from modern (< 150 ybp) to Middle Middle through Early Middle Pleistocene (∼ 300 ka to ∼ 770 ka). Marietta has terrace ages ranging from modern (< 150 ybp) to Early Pleistocene through Late Pliocene (∼ 770 ka to ∼ 2400 ka).     

Identifying run‐off contributions during melt‐induced run‐off events in a glacierized alpine catchment

We analysed contributions to run‐off using hourly stream water samples from seven individual melt‐induced run‐off events (plus one rainfall event) during 2011, 2012 and 2013 in two nested glacierized catchments in the Eastern Italian Alps. Electrical conductivity and stable isotopes of water were used for mixing analysis and two‐component and three‐component hydrograph separation. High‐elevation snowmelt, glacier melt and autumn groundwater were identified as major end‐members. Discharge and tracers in the stream followed the diurnal variations of air temperature but markedly reacted to rainfall inputs. Hysteresis patterns between discharge and electrical conductivity during the melt‐induced run‐off events revealed contrasting loop directions at the two monitored stream sections. Snowmelt contribution to run‐off was highest in June and July (up to 33%), whereas the maximum contribution of glacier melt was reached in August (up to 65%). The maximum groundwater and rainfall contributions were 62% and 11%, respectively. Run‐off events were generally characterized by decreasing snowmelt and increasing glacier melt fractions from the beginning to the end of the summer 2012, while run‐off events in 2013 showed less variable snowmelt and lower glacier melt contributions than in 2012. The results provided essential insights into the complex dynamics of melt‐induced run‐off events and may be of further use in the context of water resource management in alpine catchments. Copyright © 2015 John Wiley & Sons, Ltd.