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  • 1
    Publication Date: 2018-06-20
    Print ISSN: 1742-464X
    Electronic ISSN: 1742-4658
    Topics: Biology , Chemistry and Pharmacology , Medicine
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  • 2
    Publication Date: 2016-07-07
    Description: The Compact Dual Ion Composition Experiment – CoDICE – simultaneously provides high quality plasma and energetic ion composition measurements over six decades in energy in a wide variety of space plasma environments. CoDICE measures two critical ion populations in space plasmas: 1) Elemental and charge state composition, and 3D velocity distributions of 〈10 eV/q–40 keV/q plasma ions; and 2) Elemental composition, energy spectra and angular distributions of ∼30 keV–〉10 MeV energetic ions. CoDICE uses a novel, integrated, common time-of-flight subsystem that provides several advantages over the commonly used separate plasma and energetic ion sensors currently flying on several space missions. These advantages include reduced mass and volume compared to two separate instruments, reduced shielding in high radiation environments, and simplified spacecraft interface and accommodation requirements. This paper describes the operation principles, electro-optic simulation results, and applies the CoDICE concept for measuring plasma and energetic ion populations in Jupiter's magnetosphere.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2016-06-29
    Description: Fog drip is recognized as an important source of water for many ecosystems that often harbor a disproportionate fraction of endemic species. Characterizing and quantifying the ecological importance of fog drip in these ecosystems requires a range of approaches. We report on a multi-faceted study of Bishop pine ( Pinus muricata D. Don) along a coastal-inland transect on an island off Southern California. Hourly sampling included micrometeorology, sap flux, and soil moisture. Monthly measurements included changes in tree girth, plant water stress, and isotopic values of fogwater, rainwater, and xylem water. These data show that summertime fog drip clearly affected soil moisture and maintained aspects of tree function, including leaf water relations, sap flux dynamics, and growth rates. Although water from fog drip to the soil surface was occasionally taken up by pine trees, as quantified with isotopic measurements and a Bayesian mixing model, this utilization of fog drip was highly variable in space and time. The proportion of fogwater inferred to have been used is also much less than has been demonstrated in more mesic coastal forest ecosystems using isotopic methods. These results thus suggest high ecosystem sensitivity to even moderate amounts of fog drip, a finding with important implications as climate change differentially affects fog and rain patterns.
    Electronic ISSN: 2150-8925
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 4
    Publication Date: 2016-05-05
    Description: This study provides the first observations of Plutogenic ions and their unique interaction with the solar wind. We find ~20% solar wind slowing that maps to a point only ~4.5 R P upstream of Pluto and a bow shock most likely produced by comet-like mass loading. The Pluto obstacle is a region of dense heavy ions bounded by a “Plutopause” where the solar wind is largely excluded, and which extends back 〉100 R P into a heavy ion tail. The upstream standoff distance is at only ~2.5 R P . The heavy ion tail contains considerable structure, may still be partially threaded by the IMF, and is surrounded by a light ion sheath. The heavy ions (presumably CH 4 + ) have average speed, density, and temperature of ~90 km s -1 , ~0.009 cm -3 , and ~7x10 5 K, with significant variability, slightly increasing speed/temperature with distance and are N-S asymmetric. Density and temperature are roughly anti-correlated yielding a pressure ~2 x10 -2 pPa, roughly in balance with the interstellar pickup ions at ~33 AU. We set an upper bound of 〈30 nT surface field at Pluto and argue that the obstacle is largely produced by atmospheric thermal pressure like Venus and Mars; we also show that the loss rate down the tail (~5 x10 23 s -1 ) is only ~1% of the expected total CH 4 loss rate from Pluto. Finally, we observe a burst of heavy ions upstream from the bow shock as they are becoming picked up and tentatively identify an IMF outward sector at the time of the NH flyby.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2016-05-12
    Description: Carbon foils have been successfully used for several decades in space plasma instruments to detect ions and neutral atoms. These instruments take advantage of two properties of the particle-foil interaction: charge conversion of neutral atoms and/or secondary electron emission. This interaction also creates several adverse effects for the projectile exiting the foil, such as angular scattering and energy straggling, that usually act to reduce the sensitivity and overall performance of an instrument. The magnitude of these effects mainly varies with the incident angle, energy, and mass of the incoming projectile and the foil thickness. In this paper, we describe these effects and the properties of the interaction. We also summarize results from recent studies with graphene foils, which can be made thinner than carbon foils due to their superior strength. Graphene foils may soon replace carbon foils in space plasma instruments and open new opportunities for space research in the future.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2019
    Description: Abstract We present a continuing investigation of mass‐/charge‐dependent interactions between energetic ions (greater than tens of kiloelectron volts) and planetary magnetopauses and of the escape of the ions across the boundary. Previous studies at Earth using Magnetospheric Multiscale mission data are refined and advanced showing profound behavior differences between light (H, He) and singly charged heavy ions (O+). We highlight a distinctive feature of oxygen ions: an angular distribution bifurcation providing clear indication of entrainment along the magnetopause in Speiser‐like orbits during relatively stable magnetic conditions. This signature, interpreted using a simple kinetic model, suggests that these ions tend to be carried substantial distances along the boundary (even with boundary‐normal magnetic fields) in a fashion that impedes their full dayside escape. While large fluctuations and waves can likely sometimes disrupt the observed ordering, the following picture emerges. Energetic particles with gyroradii much smaller than the magnetopause thickness (e.g., electrons and absent boundary‐normal magnetic fields) and ions with gyroradii much larger than the thickness (e.g., O+) are impeded from fully escaping across the boundary. However, energetic ions with intermediate‐sized gyroradii commensurate with the thickness (e.g., H+, He++, and O6+) can be effectively scattered within the boundary causing them to escape much more readily, with and without boundary‐normal fields. This picture is supported by observations from the Juno spacecraft at the near‐dawn meridian side of Jupiter's magnetopause. There it is observed that energetic electrons and heavy ions are more strongly contained by the magnetopause than are the energetic protons and helium ions.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2019
    Description: Abstract Statistical analysis of geomagnetic paleosecular variation (PSV) and time averaged field (TAF) has been largely based on global compilations of paleomagnetic data from lava flows. These show different trends in the averaged inclination anomaly (ΔI) between the two hemispheres, with small positive (〈2°) anomalies in mid‐southern latitudes and large negative (〉‐5°) anomalies in mid‐northern latitudes. To inspect the large ΔI between 20°N‐40°N we augment the global data with a new paleomagnetic dataset from the Golan‐Heights (GH), a Plio‐Pleistocene volcanic plateau in northeast Israel, located at 32°N‐33°N. The GH dataset consists of 91 lava flows sites: 40 sites obtained in the 1990s and 51 obtained in this study. The chronology of the flows is constrained by 57 40Ar/39Ar ages: 39 from previous studies and 18 from this study, which together cover most of the GH plateau. We show that the 1990s dataset might be affected by block rotations and does not fully sample PSV. The Plio‐Pleistocene pole (86.3°N, 120.8°E, N=44, k=25, α95=4.4°), calculated after applying selection criteria with Fisher precision parameter (k) ≥ 100 and number of specimens per site (n) ≥ 5 is consistent with a geocentric axial dipole field and shows smaller inclination anomaly (ΔI=‐0.4°) than predicted by global compilations and PSV models. Re‐examination of the inclination anomaly in the global compilation using different calculation methods and selection criteria suggests that inclination anomaly values are affected by: (1) inclusion of poor quality data, (2) averaging data by latitude bins and (3) the way the inclination anomaly is calculated.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2019
    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).
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2019
    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.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    Publication Date: 2019
    Description: Abstract Previous work has shown that the Madden‐Julian Oscillation (MJO) can influence the North Atlantic Oscillation (NAO) via a Rossby wave teleconnection that propagates through the troposphere (i.e., a tropospheric pathway). In addition, recent work suggests that the MJO can influence the stratospheric polar vortex, which is also known to influence the tropospheric NAO—thus, there likely exists a stratospheric pathway for MJO influence as well. Here, we apply two methods to shed more light on the pathways linking the MJO to the NAO. First, we use a traditional approach in climate science based on analyzing conditional probabilities. Second, we use methods from causal discovery theory based on probabilistic graphical models. Together, these two analysis approaches reveal that the MJO can impact the NAO via both a tropospheric and stratospheric pathway. The stratospheric pathway is shown to come about in two ways: First, both methods show that the MJO itself influences the strength of the stratospheric polar vortex on a timescale of ∼10 days, and then 5 days later the vortex can drive changes in the NAO. Second, the state of the stratospheric polar vortex acts to condition the NAO to be conducive (or not) to MJO influence. When the vortex is in a state that opposes the expected NAO response to the MJO, we find little influence of the MJO on the NAO, however, when the vortex supports the expected NAO response, the NAO is up to 30% more likely to be in a particular state following active MJO periods.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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