ALBERT

Description: Abstract The Jovian Auroral Distributions Experiment Ion sensor (JADE‐I) on Juno is a plasma instrument that measures the energy‐per‐charge (E/Q) distribution of 0.01 to 46.2 keV/q ions over a mass‐per‐charge (M/Q) range of 1 – 64 amu/q. However, distinguishing O+ and S2+ from JADE‐I's measurements is a challenging task due to similarities in their M/Q (≈ 16 amu/q). Because of this, O+ and S2+ have not been fully resolved in the in‐situ measurements made by plasma instruments at Jupiter (e.g., Voyager PLS and Galileo PLS) and their relative ratios has been studied using physical chemistry models and UV remote observations. To resolve this ambiguity, a ray‐tracing simulation combined with carbon foil effects is developed and used to obtain instrument response functions for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+. The simulation results indicate that JADE‐I can resolve the $M/Q$ ambiguity between O+ and S2+ due to a significant difference in their charge state modification process and a presence of a large electric potential difference (≈ 8 kV) between its carbon foils and MCPs. A forward model based on instrument response functions and eight convected kappa distributions is then used to obtain ion properties at the equatorial plasma sheet (≈ 36 jovian radii) in the pre‐dawn sector of magnetosphere. The number density ratio between O+ and S2+ for the selected plasma sheet crossings ranges from 0.2 to 0.7 (mean value 0.37 ± 0.12) and the number density ratio between total oxygen ions to total sulfur ions ranges from 0.2 to 0.6 (0.41 ±0.09).

Description: Abstract The low‐altitude, high‐velocity trajectory of the Juno spacecraft enables the Jovian Auroral Distributions Experiment to make the first in situ observations of the high‐latitude ionospheric plasma. Ions are observed to energies below 1 eV. The high‐latitude ionospheric ions are observed simultaneously with a loss cone in the magnetospheric ions, suggesting precipitating magnetospheric ions contribute to the heating of the upper ionosphere, raising the scale height, and pushing ionospheric ions to altitudes of 0.5 RJ above the planet where they are observed by Jovian Auroral Distributions Experiment. The source of the magnetospheric ions is tied to the Io torus and plasma sheet, indicated by the cutoff seen in both the magnetospheric and ionospheric plasma at the Io M‐shells. Equatorward of the Io M‐shell boundary, the ionospheric ions are not observed, indicating a drop in the scale height of the ionospheric ions at those latitudes.

Description: We present a new waveform inversion technique to estimate the energy of near-surface explosions using atmospheric acoustic waves. Conventional methods often employ air-blast models based on a homogeneous atmosphere, where the acoustic wave propagation effects (e.g., refraction and diffraction) are not taken into account and therefore their accuracy decreases with increasing source-receiver distance. In this study, three-dimensional acoustic simulations are performed with a finite-difference method in realistic atmospheres and topography, and the modeled acoustic Green's functions are incorporated into the waveform inversion for the acoustic source-time functions. The strength of the acoustic source is related to explosion yield based on a standard air-blast model. The technique was applied to local explosions (〈10km) and provided reasonable yield estimates (〈∼30% error) in the presence of realistic topography and atmospheric structure. The presented method can be extended to explosions recorded at far distance provided proper meteorological specifications.

Description: We describe a practical system for forecasting peak intensity and fluence of solar energetic protons in the tens to hundreds of MeV energy range. The system could be useful for forecasting radiation hazard, because peak intensity and fluence are closely related to the medical physics quantities peak dose rate and total dose. The method uses a pair of ground-based detectors located at the South Pole to make a measurement of the solar particle energy spectrum at relativistic (GeV) energies, and it then extrapolates this spectrum downward in energy to make a prediction of the peak intensity and fluence at lower energies. A validation study based upon 12 large solar particle events compared the prediction with measurements made aboard GOES spacecraft. This study shows that useful predictions (logarithmic correlation greater than 50%) can be made down to energies of 40–80 MeV (GOES channel P5) in the case of peak intensity, with the prediction leading the observation by 166 min on average. For higher energy GOES channels, the lead times are shorter, but the correlation coefficients are larger.

Description: Numerical modeling of waveform diffractions along the rim of a volcano vent shows high correlation to observed explosion signals at Karymsky Volcano, Kamchatka, Russia. The finite difference modeling assumed a gaussian source time function and an axisymmetric geometry. A clear demonstration of the significant distortion of infrasonic wavefronts was caused by diffraction at the vent rim edge. Data collected at Karymsky in 1997 and 1998 were compared to synthetic waveforms and variations of vent geometry were determined via grid search. Karymsky exhibited a wide range of variation in infrasonic waveforms, well explained by the diffraction, and modeled as changing vent geometry. Rim diffraction of volcanic infrasound is shown to be significant and must be accounted for when interpreting source physics from acoustic observations.

Description: Partitioning of CO 2 exchange into canopy ( F A ) and soil ( F R ) flux components is essential to improve our understanding ecosystem processes. The stable isotope C 18 OO can be used for flux partitioning, but this approach depends on the magnitude and consistency of the isotope disequilibrium ( D eq ), i.e. difference between the isotope compositions of F R ( δ A ) and F A ( δ R ). In this study high temporal resolution isotopic data were used: 1) to test the suitability of existing steady state and non-steady models to estimate H 2 18 O enrichment in a mixed forest canopy, 2) to investigate the temporal dynamics of δ A using a big-leaf parameterization, and 3) to quantify the magnitude of the C 18 OO disequilibrium ( D eq ) in a temperate deciduous forest throughout the growing season and to determine the sensitivity of this variable to the CO 2 hydration efficiency ( θ eq ). A departure from steady state conditions was observed even at mid-day in this study, so the non-steady state formulation provided better estimates of leaf water isotope composition. The dynamics of δ R was mainly driven by changes in soil water isotope composition, caused by precipitation events. Large D eq values (up to 11‰) were predicted; however the magnitude of the disequilibrium was variable throughout the season. The magnitude of D eq was also very sensitive to the hydration efficiencies in the canopy. For this temperate forest during most of the growing season, the magnitude of D eq was inversely proportional to θ eq , due to the very negative δ R signal, which is contrary to observations for other ecosystems investigated in previous studies.

Description: Observations of interplanetary scintillation (IPS) provide a set of data that are used in estimating the solar wind parameters with reasonably good accuracy. Various tomography techniques have been developed to deconvolve the line-of-sight integration effects ingrained in observations of IPS to improve the accuracy of solar wind reconstructions. Among those, the time-dependent tomography developed at the University of California, San Diego (UCSD) is well-known for its remarkable accuracy in reproducing the solar wind speed and density at Earth by iteratively fitting a kinematic solar wind model to observations of IPS and near-Earth spacecraft measurements. However, the kinematic model gradually breaks down as the distance from the Sun increases beyond the orbit of Earth. Therefore, it would be appropriate to use a more sophisticated model, such as a magnetohydrodynamics (MHD) model, to extend the kinematic solar wind reconstruction beyond the Earth's orbit and to the outer heliosphere. To testthe suitability of this approach, we use boundary conditions provided by the UCSD time-dependent tomography to propagate the solar wind outward in a MHD model and compare the simulation results with in situ measurements and also with the corresponding kinematic solution. Interestingly, we find notable differences in proton radial velocity and number density at Earth and various locations in the inner heliosphere between the MHD results and both the in situ data and thekinematic solution. For example at 1 AU, the MHD velocities are generally larger than the spacecraft data by up to 150 km s −1 , and the amplitude of density fluctuations is also markedly larger in the MHD solution. We show that the MHD model can deliver more reasonable results at Earth with an ad hoc adjustment of the inner boundary values. However, we conclude that the MHD model using the inner boundary conditions derived from kinematic simulations has little chance to match IPS and textitin situ data as well as the kinematic model does unless it too is iteratively fit to the observational data and measurements.

Description: Whistler-mode chorus waves are considered to play a central role in accelerating and scattering electrons in the outer radiation belt. While in-situ measurements are usually limited to the trajectories of a small number of satellites, rigorous theoretical modeling requires a global distribution of chorus wave characteristics. In the present work, by using a large database of chorus wave observations made on the THEMIS satellites for about five years, we develop prediction models for a global distribution of chorus amplitudes. The development is based on two main components: a) the temporal dependence of average chorus amplitudes determined by correlating with the preceding solar wind and geomagnetic conditions as represented by the IMF B z and AE index; b) the determination of spatial distribution pattern of chorus amplitudes, specifically, the profiles in L in all 2 hr MLT zones, which are categorized by activity levels of either the IMF B z or AE index. Two separate models are developed: one based only on the IMF B z and the other based only on AE . Both models predict chorus amplitudes for two different latitudinal zones separately: |MLAT| 〈 10 o , and |MLAT| = 10 o - 25 o . The model performance is measured by the coefficient of determination R 2 and the rank-order correlation coefficient (ROCC) between the observations and model prediction results. When tested for a new data interval of ~1.5 years, the AE -based model works slightly better than the IMF B z -based model: for the AE -based model, the mean R 2 and ROCC values are ~0.46 and ~0.78 for |MLAT| 〈 10 o , respectively, and ~0.4 and ~0.74 for |MLAT| = 10 o - 25 o , respectively; for the IMF B z -based model, the mean R 2 and ROCC values are ~0.39 and ~0.74 for |MLAT| 〈 10 o , respectively, and ~0.33 and ~0.70 for |MLAT| = 10 o - 25 o , respectively. We provide all of the model information in the text and supporting materials so that the developed chorus models can be used for the existing outer radiation belt electron models.

Description: A disposable iron-based catalyst, red mud, was modified by different dissolution-precipitation methods. The catalysts obtained were characterized by nitrogen adsorption, X-ray diffraction, scanning electron microscopy, and ammonia temperature-programmed desorption. They were tested for slurry-phase hydrocracking of vacuum residue in a batch reactor. The red-mud catalyst activated by phosphoric acid showed the highest catalytic activity since the activation by phosphoric acid resulted in the decrease in particle size which facilitated the transformation of red mud to the active sulfide form in the reaction. Different dissolution-precipitation methods served for modification of a disposable iron-based catalyst, red mud. The resulting materials were evaluated as catalysts for the slurry-phase catalytic hydrocracking of vacuum residue. Red mud activated by phosphoric acid treatment exhibited the best performance due to the caused particle size reduction.

Description: Abstract Acoustic waveform inversions can provide estimates of volume flow rate and erupted mass, enhancing the ability to estimate volcanic emissions. Previous studies have generally assumed a simple acoustic source (monopole); however, more complex and accurate source reconstructions are possible with a combination of equivalent sources (multipole). We deployed a high‐density acoustic network around Yasur volcano, Vanuatu, including acoustic sensors on a tethered aerostat that was moved every ~15‐60 minutes. Using this unique dataset we invert for the acoustic multipole source mechanism using a grid‐search approach for 80 events to examine volume flow rates and dipole strengths. Our method utilizes Finite‐Difference Time‐Domain modeling to obtain the full 3‐D Green's functions that account for topography. Inversion results are compared using a monopole‐only, multipole (monopole and dipole), simulations that do not include topography, and those that use a subset of sensors. We find that the monopole source is a good approximation when topography is considered. However, initial compression amplitude is not fully captured by a monopole source so source directionality cannot be ruled out. The monopole solution is stable regardless of whether a monopole‐only or multipole inversion is performed. Inversions for the dipole components produce estimates consistent with observed source directionality, though these inversions are somewhat unstable given station configurations of typical deployments. Our results suggest infrasound waveform inversion shows promise for realistic quantitative source estimates, but additional work is necessary to fully explore inversion stability, uncertainty, and robustness.