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Journal articleCarr CM, Erikksson S, Lapenta G, et al., 2015, , The Astrophysical Journal, Vol: 805, ISSN: 0004-637X
We report new multi-spacecraft Cluster observations of tripolar guide magnetic field perturbations at a solar windreconnection exhaust in the presence of a guide field BM which is almost four times as strong as the reversing fieldBL. The novel tripolar field consists of two narrow regions of depressed BM, with an observed 7%–14% ΔBMmagnitude relative to the external field, which are found adjacent to a wide region of enhanced BM within theexhaust. A stronger reversing field is associated with each BM depression. A kinetic reconnection simulation forrealistic solar wind conditions and the observed strong guide field reveals that tripolar magnetic fields preferentiallyform across current sheets in the presence of multiple X-lines as magnetic islands approach one another and mergeinto fewer and larger islands. The simulated ΔBM/ΔXN over the normal width ΔXN between a BM minimum andthe edge of the external region agree with the normalized values observed by Cluster. We propose that a tripolarguide field perturbation may be used to identify candidate regions containing multiple X-lines and interactingmagnetic islands at individual solar wind current sheets with a strong guide field.
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Journal articleArcher M, Plaschke F, 2015, , Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 3632-3646, ISSN: 2169-9380
It is has been proposed that the subsolar magnetopause may support its own eigenmode, consisting of propagating surface waves which reflect at the northern/southern ionospheres forming a standing wave. While the eigenfrequencies of these so鈥恈alled Kruskal鈥怱chwarzschild (KS) modes have been estimated under typical conditions, the potential distribution of frequencies over the full range of solar wind conditions is not known. Using models of the magnetosphere and magnetosheath applied to an entire solar cycle's worth of solar wind data, we perform time鈥恛f鈥恌light calculations yielding a database of KS mode frequencies. Under nonstorm times or northward interplanetary magnetic field (IMF), the most likely fundamental frequency is calculated to be urn:x-wiley:jgra:media:jgra51793:jgra51793-math-0001 mHz, consistent with previous estimates and indirect observational evidence for such standing surface waves of the subsolar magnetopause. However, the distributions exhibit significant spread (of order ±0.3 mHz) demonstrating that KS mode frequencies, especially higher harmonics, should vary considerably depending on the solar wind conditions. The implications of such large spread on observational statistics are discussed. The subsolar magnetopause eigenfrequencies are found to be most dependent on the solar wind speed, southward component of the IMF, and the Dst index, with the latter two being due to the erosion of the magnetosphere by reconnection and the former an effect of the expression for the surface wave phase speed. Finally, the possible occurrence of KS modes is shown to be controlled by the dipole tilt angle.
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Journal articleFranci L, Verdini A, Matteini L, et al., 2015, , Astrophysical Journal Letters, Vol: 804, ISSN: 2041-8213
We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) twodimensionalnumerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smoothbreak at proton scales) develop with clear power-law scaling, each one occupying about a decade in wavenumbers.The simulation results simultaneously exhibit several properties of the observed solar wind fluctuations: spectralindices of the magnetic, kinetic, and residual energy spectra in the magnetohydrodynamic (MHD) inertial rangealong with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong couplingof the cascade with the density and the parallel component of the magnetic fluctuations at sub-proton scales. Ourfindings support the interpretation that in the solar wind, large-scale MHD fluctuations naturally evolve beyondproton scales into a turbulent regime that is governed by the generalized Ohm’s law
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Journal articleTong Y, Bale SD, Chen CHK, et al., 2015, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 804, ISSN: 2041-8205
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- Citations: 12
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Journal articleFletcher L, Cargill PJ, Antiochos SK, et al., 2015, , SPACE SCIENCE REVIEWS, Vol: 188, Pages: 211-249, ISSN: 0038-6308
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- Citations: 19
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Journal articleCzaja A, Marshall J, 2015, , OCEAN DYNAMICS, Vol: 65, Pages: 751-760, ISSN: 1616-7341
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- Citations: 7
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Journal articleHu F, Sun J, Brindley HE, et al., 2015, , JOURNAL OF INFRARED MILLIMETER AND TERAHERTZ WAVES, Vol: 36, Pages: 474-495, ISSN: 1866-6892
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- Citations: 12
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Journal articleBalogh A, Bykov A, Eastwood J, et al., 2015, , SPACE SCIENCE REVIEWS, Vol: 188, Pages: 1-2, ISSN: 0038-6308
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Journal articleEastwood JP, Hietala H, Toth G, et al., 2015, , SPACE SCIENCE REVIEWS, Vol: 188, Pages: 251-286, ISSN: 0038-6308
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- Citations: 49
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Journal articleHeiter U, Lind K, Asplund M, et al., 2015, , PHYSICA SCRIPTA, Vol: 90, ISSN: 0031-8949
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- Citations: 132
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Journal articleHartinger MD, Plaschke F, Archer MO, et al., 2015, , GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 2594-2602, ISSN: 0094-8276
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- Citations: 35
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Journal articleMasters A, 2015, , GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 2577-2585, ISSN: 0094-8276
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- Citations: 20
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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 – 鈭 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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