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Journal articleWang L, Yang L, He J, et al., 2015, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 803, ISSN: 2041-8205
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- Citations: 41
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Journal articleJackman CM, Thomsen MF, Mitchell DG, et al., 2015, , Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 3603-3617, ISSN: 2169-9402
We present a case study of an event from 20 August (day 232) of 2006, when the Cassini spacecraft was sampling the region near 32 RS and 22 h LT in Saturn's magnetotail. Cassini observed a strong northward-to-southward turning of the magnetic field, which is interpreted as the signature of dipolarization of the field as seen by the spacecraft planetward of the reconnection X line. This event was accompanied by very rapid (up to ~1500 km s−1) thermal plasma flow toward the planet. At energies above 28 keV, energetic hydrogen and oxygen ion flow bursts were observed to stream planetward from a reconnection site downtail of the spacecraft. Meanwhile, a strong field-aligned beam of energetic hydrogen was also observed to stream tailward, likely from an ionospheric source. Saturn kilometric radiation emissions were stimulated shortly after the observation of the dipolarization. We discuss the field, plasma, energetic particle, and radio observations in the context of the impact this reconnection event had on global magnetospheric dynamics.
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Journal articleChadney, Galand M, Unruh YC, et al., 2015, , Icarus, Vol: 250, Pages: 357-367, ISSN: 1090-2643
Upper atmospheres of Hot Jupiters are subject to extreme radiation conditions that can result in rapid atmospheric escape. The composition and structure of the upper atmospheres of these planets are affected by the high-energy spectrum of the host star. This emission depends on stellar type and age, which are thus important factors in understanding the behaviour of exoplanetary atmospheres. In this study, we focus on Extrasolar Giant Planets (EPGs) orbiting K and M dwarf stars. XUV spectra for three different stars – Eridani, AD Leonis and AU Microscopii – are constructed using a coronal model. Neutral density and temperature profiles in the upper atmosphere of hypothetical EGPs orbiting these stars are then obtained from a fluid model, incorporating atmospheric chemistry and taking atmospheric escape into account. We find that a simple scaling based solely on the host star’s X-ray emission gives large errors in mass loss rates from planetary atmospheres and so we have derived a new method to scale the EUV regions of the solar spectrum based upon stellar X-ray emission. This new method produces an outcome in terms of the planet’s neutral upper atmosphere very similar to that obtained using a detailed coronal model of the host star. Our results indicate that in planets subjected to radiation from active stars, the transition from Jeans escape to a regime of hydrodynamic escape at the top of the atmosphere occurs at larger orbital distances than for planets around low activity stars (such as the Sun).
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Journal articleRiley P, Lionello R, Linker JA, et al., 2015, , ASTROPHYSICAL JOURNAL, Vol: 802, ISSN: 0004-637X
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- Citations: 63
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Journal articlePisa D, Hospodarsky GB, Kurth WS, et al., 2015, , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 120, Pages: 2531-2542, ISSN: 2169-9380
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- Citations: 8
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Journal articleYates JN, Southwood DJ, Dougherty MK, 2015, , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 120, Pages: 2631-2648, ISSN: 2169-9380
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- Citations: 6
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Journal articleDelamere PA, Bagenal F, Paranicas C, et al., 2015, , SPACE SCIENCE REVIEWS, Vol: 187, Pages: 51-97, ISSN: 0038-6308
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- Citations: 51
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Journal articleFox C, Green PD, Pickering JC, et al., 2015, , JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, Vol: 155, Pages: 57-65, ISSN: 0022-4073
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- Citations: 9
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Journal articleKimura T, Badman SV, Tao C, et al., 2015, , GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 1662-1668, ISSN: 0094-8276
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- Citations: 57
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Journal articleCui J, Galand M, Yelle RV, et al., 2015, , Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 2333-2346, ISSN: 2169-9402
The nightside Martian ionosphere is thought to be contributed by day-to-night transport and electron precipitation, of which the former has not been well studied. In this work, we evaluate the role of day-to-night transport based on the total electron content (TEC) measurements made by the Mars Advanced Radar for Subsurface and Ionospheric Sounding on board Mars Express. This is accomplished by an examination of the variation of nightside TEC in the time domain rather than the traditional solar zenith angle domain. Our analyses here, being constrained to the Northern Hemisphere where the effects of crustal magnetic fields can be neglected, reveal that day-to-night transport serves as the dominant source for the nightside Martian ionosphere from terminator crossing up to time in darkness of ≈5.3 × 103 s, beyond which it is surpassed by electron precipitation. The observations are compared with predictions from a simplified time-dependent ionosphere model. We conclude that the solid body rotation of Mars is insufficient to account for the observed depletion of nightside TEC but the data could be reasonably reproduced by a zonal electron flow velocity of ≈1.9 km s−1.
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Journal articleMatteini L, Horbury TS, Pantellini F, et al., 2015, , Astrophysical Journal, Vol: 802, ISSN: 1538-4357
We investigate the properties of plasma fluid motion in the large-amplitude, low-frequency fluctuations of highlyAlfvénic fast solar wind. We show that protons locally conserve total kinetic energy when observed from aneffective frame of reference comoving with the fluctuations. For typical properties of the fast wind, this frame canbe reasonably identified by alpha particles which, due to their drift with respect to protons at about the Alfvénspeed along the magnetic field, do not partake in the fluid low-frequency fluctuations. Using their velocity totransform the proton velocity into the frame of Alfvénic turbulence, we demonstrate that the resulting plasmamotion is characterized by a constant absolute value of the velocity, zero electric fields, and aligned velocity andmagnetic field vectors as expected for unidirectional Alfvénic fluctuations in equilibrium. We propose that thisconstraint, via the correlation between velocity and magnetic field in Alfvénic turbulence, is the origin of theobserved constancy of the magnetic field; while the constant velocity corresponding to constant energy can only beobserved in the frame of the fluctuations, the corresponding constant total magnetic field, invariant for Galileantransformations, remains the observational signature in the spacecraft frame of the constant total energy in theAlfvén turbulence frame
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Journal articleGingell PW, Burgess D, Matteini L, 2015, , ASTROPHYSICAL JOURNAL, Vol: 802, ISSN: 0004-637X
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- Citations: 20
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Journal articleMartinez-Oliveros JC, Raftery C, Bain H, et al., 2015, , SOLAR PHYSICS, Vol: 290, Pages: 891-901, ISSN: 0038-0938
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- Citations: 5
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Journal articleNazarenko L, Schmidt GA, Miller RL, et al., 2015, , JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS, Vol: 7, Pages: 244-267
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- Citations: 117
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Journal articleCui J, Galand M, Zhang SJ, et al., 2015, , Journal of Geophysical Research: Planets, Vol: 120, Pages: 278-286, ISSN: 2169-9100
We propose a revised Chapman model for the ionosphere of Mars by allowing for vertical variation of electron temperature. An approximate energy balance between solar EUV heating and CO2 collisional cooling is applied in the dayside Martian ionosphere, analogous to the method recently proposed by Withers et al. (2014). The essence of the model is to separate the contributions of the neutral and electron thermal structures to the apparent width of the main ionospheric layer. Application of the model to the electron density profiles from the Mars Global Surveyor (MGS) radio occultation measurements reveals a clear trend of elevated electron temperature with increasing solar zenith angle (SZA). It also reveals that the characteristic length scale for the change of electron temperature with altitude decreases with increasing SZA. These observations may imply enhanced topside heat influx near the terminator, presumably an outcome of the solar wind interactions with the Martian upper atmosphere. Our analysis also reveals a tentative asymmetry in electron temperature between the northern and southern hemispheres, consistent with the scenario of elevated electron temperature within minimagnetospheres.
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Conference paperPickering JC, Fox C, Murray JE, et al., 2015,
The cirrus coupled cloud-radiation experiment: CIRCCREX
We report early results from the Cirrus Coupled Cloud-Radiation Experiment CIRCCREX investigating cirrus through airborne campaigns including radiation measurements (0.3-125μm). Cirrus models and parameterizations used in radiative transfer codes and numerical weather prediction will be tested.
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Journal articleGoldberg SJ, Ball GI, Allen BC, et al., 2015, , Nature Communications, Vol: 6, ISSN: 2041-1723
The role of dissolved organic matter (DOM) as either a sink for inorganic nutrients or anadditional nutrient source is an often-neglected component of nutrient budgets in aquaticenvironments. Here, we examined the role of DOM in reactive nitrogen (N) storage in SierraNevada (California, USA) lakes where atmospheric deposition of N has shifted the lakestoward seasonal phosphorus (P)-limitation. Nuclear magnetic resonance (NMR) spectroscopyand isotope analyses performed on DOM isolated from Lake Tahoe reveal the accumulationof refractory proteinaceous material with a 100–200-year residence time. Incontrast, smaller lakes in the same watershed contain DOM with typical terrestrial characteristics,indicating that proteins in Lake Tahoe are autochthonously produced. These datasupport the role of DOM as a possible sink for reactive N in these lake ecosystems andidentify a potential role for DOM in affecting the inorganic nutrient stoichiometry of theseenvironments.
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Conference paperPickering JC, Fox C, Murray JE, et al., 2015,
We report early results from the Cirrus Coupled Cloud-Radiation Experiment CIRCCREX investigating cirrus through airborne campaigns including radiation measurements (0.3-125μm). Cirrus models and parameterizations used in radiative transfer codes and numerical weather prediction will be tested.
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Conference paperPickering JC, Mushtaq S, Steers EBM, et al., 2015,
High resolution FTS studies of the effects of trace molecular gases on Glow Discharge spectra and industrial applications
Analytical Glow Discharge (GD) Optical Emission Spectroscopy and GD Mass Spectrometry have important industrial applications. The analytical accuracy may be affected by trace molecular gases. High resolution FTS is used to investigate fundamental discharge processes.
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Conference paperPickering JC, Mushtaq S, Steers EBM, et al., 2015,
Analytical Glow Discharge (GD) Optical Emission Spectroscopy and GD Mass Spectrometry have important industrial applications. The analytical accuracy may be affected by trace molecular gases. High resolution FTS is used to investigate fundamental discharge processes.
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Book chapterSouthwood DJ, 2015,
Formation of Magnetotails: Fast and Slow Rotators Compared
, Magnetotails in the Solar System, Editors: Keiling, Jackman, Publisher: John Wiley & Sons, Pages: 199-215, ISBN: 9781118842348 -
Journal articleBrindley H, Bantges R, Russell J, et al., 2015, , JOURNAL OF CLIMATE, Vol: 28, Pages: 1649-1660, ISSN: 0894-8755
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- Citations: 15
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Journal articleEastwood JP, Goldman MV, Hietala H, et al., 2015, , Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 511-525, ISSN: 2169-9402
Dipolarization fronts (DFs) are often associated with the leading edge of earthward bursty bulk flows in the magnetotail plasma sheet. Here multispacecraft Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations are used to show that a spatially limited region of counterpropagating ion beams, whose existence is not evident in either the plasma moments or the electric field, is observed on the low-density side of DFs. The THEMIS magnetic field data are used to establish appropriate comparison cuts through a particle-in-cell simulation of reconnection, and very good agreement is found between the observed and simulated ion distributions on both sides of the DF. Self-consistent back tracing shows that the ion beams originate from the thermal component of the preexisting high-density plasma into which the DF is propagating; they do not originate from the inflow region in the traditional sense. Forward tracing shows that some of these ions can subsequently overtake the DF and pass back into the high-density preexisting plasma sheet with an order-of-magnitude increase in energy; this process is distinct from other ion reflection processes that occur directly at the DF. The interaction of the reconnection jet with the preexisting plasma sheet therefore occurs over a macroscopic region, rather than simply being limited to the thin DF interface. A more general consequence of this study is the conclusion that reconnection jets are not simply fed by plasma inflow across the separatrices but are also fed by plasma from the region into which the jet is propagating; the implications of this finding are discussed.
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Journal articleBertucci C, Hamilton DC, Kurth WS, et al., 2015, , GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 193-200, ISSN: 0094-8276
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- Citations: 42
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Journal articleNilsson H, Wieser GS, Behar E, et al., 2015, , Science, Vol: 347, ISSN: 0036-8075
The Rosetta mission shall accompany comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 astronomical units through perihelion passage at 1.25 astronomical units, spanning low and maximum activity levels. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation, until the size and plasma pressure of the ionized atmosphere define its boundaries: A magnetosphere is born. Using the Rosetta Plasma Consortium ion composition analyzer, we trace the evolution from the first detection of water ions to when the atmosphere begins repelling the solar wind (~3.3 astronomical units), and we report the spatial structure of this early interaction. The near-comet water population comprises accelerated ions (<800 electron volts), produced upstream of Rosetta, and lower energy locally produced ions; we estimate the fluxes of both ion species and energetic neutral atoms.
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Journal articleHassig M, Altwegg K, Balsiger H, et al., 2015, , Science, Vol: 347, ISSN: 0036-8075
Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.
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Journal articleVigren E, Galand M, Lavvas P, et al., 2015, , Astrophysical Journal, Vol: 798, ISSN: 1538-4357
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Book chapterEastwood JP, Kiehas SA, 2015, , Magnetotails in the Solar System, Pages: 269-287
This chapter discusses the origin and evolution of plasmoids and flux ropes in Earth's magnetotail, providing an overview of author's current understanding based on recent multipoint and multimission data analysis. It also presents recent results concerning observations of flux ropes in the vicinity of Mars. Understanding the Mars solar wind interaction is very important for determining its atmospheric history, and recent discoveries show that magnetic reconnection-generated structures may play a significant role, particularly in the vicinity of the crustal field regions. The chapter briefly discusses some of the different terms used to describe reconnection-generated structures. It describes the production of islands, plasmoids, and secondary islands by antiparallel reconnection.
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Journal articleO'Reilly CH, Czaja A, 2015, , Quarterly Journal of the Royal Meteorological Society, Vol: 141, Pages: 52-66, ISSN: 0035-9009
An index of the Kuroshio Extension front strength is produced using a maximum covariance analysis between seasurface temperature (SST) and seasurface height (SSH) gradient observations, and composites of the atmospheric state are presented during its positive and negative phases using reanalysis data (1992–2011).It is found that when the Kuroshio Extension is less (more) meandering, with a stronger (weaker) SST front, the atmospheric heat transport by transient eddies is increased in the western (eastern) Pacific region, consistent with an increase (decrease) in lowlevel baroclinicity. Analysis of the eddy–mean flow interaction shows that this zonal shift in heat transport forces anomalous barotropic flow in the Eastern Pacific, where blocking frequency is strongly influenced.The above relationships cannot be reconciled with the known response of the North Pacific storm track to remote forcing from the Tropical Pacific, nor can they be explained by the response of the ocean to atmospheric forcing via surface heat fluxes or winds. Rather, the zonal shift in the storm track highlighted here, and the associated changes in the largescale circulation, are interpreted as a response to the interannual variability of the Kuroshio Extension front.
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Journal articleKlueser L, Banks JR, Martynenko D, et al., 2015, , REMOTE SENSING OF ENVIRONMENT, Vol: 156, Pages: 294-309, ISSN: 0034-4257
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- Citations: 20
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