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Journal articleHoraites K, Boldyrev S, Krasheninnikov SI, et al., 2015,
Self-Similar Theory of Thermal Conduction and Application to the Solar Wind
, PHYSICAL REVIEW LETTERS, Vol: 114, ISSN: 0031-9007- Author Web Link
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- Citations: 17
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Journal articleLucas DD, Kwok CY, Cameron-Smith P, et al., 2015,
Designing optimal greenhouse gas observing networks that consider performance and cost
, Geoscientific Instrumentation, Methods and Data Systems, Vol: 4, Pages: 121-137, ISSN: 2193-0864Emission rates of greenhouse gases (GHGs) enteringinto the atmosphere can be inferred using mathematicalinverse approaches that combine observations from a networkof stations with forward atmospheric transport models.Some locations for collecting observations are better thanothers for constraining GHG emissions through the inversion,but the best locations for the inversion may be inaccessibleor limited by economic and other non-scientific factors.We present a method to design an optimal GHG observingnetwork in the presence of multiple objectives that may bein conflict with each other. As a demonstration, we use ourmethod to design a prototype network of six stations to monitorsummertime emissions in California of the potent GHG1,1,1,2-tetrafluoroethane (CH2FCF3, HFC-134a). We use amultiobjective genetic algorithm to evolve network configurationsthat seek to jointly maximize the scientific accuracyof the inferred HFC-134a emissions and minimize the associatedcosts of making the measurements. The genetic algorithmeffectively determines a set of “optimal” observingnetworks for HFC-134a that satisfy both objectives (i.e., thePareto frontier). The Pareto frontier is convex, and clearlyshows the tradeoffs between performance and cost, and thediminishing returns in trading one for the other. Without dif-ficulty, our method can be extended to design optimal networksto monitor two or more GHGs with different emissionspatterns, or to incorporate other objectives and constraintsthat are important in the practical design of atmosphericmonitoring networks.
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Journal articleLucas DD, Kwok CY, Cameron-Smith P, et al., 2015,
Designing optimal greenhouse gas observing networks that consider performance and cost
, GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 4, Pages: 705-749, ISSN: 2193-0856 -
Journal articleHorbury TS, Archer MO, Brown P, et al., 2015,
The MAGIC of CINEMA: First in-flight science results from a miniaturised anisotropic magnetoresistive magnetometer
, Annales Geophysicae, Vol: 33, Pages: 725-735, ISSN: 1432-0576We present the first in-flight results from a novel miniaturised anisotropic magnetoresistive space magnetometer, MAGIC (MAGnetometer from Imperial College), aboard the first CINEMA (CubeSat for Ions, Neutrals, Electrons and MAgnetic fields) spacecraft in low Earth orbit. An attitude-independent calibration technique is detailed using the International Geomagnetic Reference Field (IGRF), which is temperature dependent in the case of the outboard sensor. We show that the sensors accurately measure the expected absolute field to within 2% in attitude mode and 1% in science mode. Using a simple method we are able to estimate the spacecraft's attitude using the magnetometer only, thus characterising CINEMA's spin, precession and nutation. Finally, we show that the outboard sensor is capable of detecting transient physical signals with amplitudes of ~ 20–60 nT. These include field-aligned currents at the auroral oval, qualitatively similar to previous observations, which agree in location with measurements from the DMSP (Defense Meteorological Satellite Program) and POES (Polar-orbiting Operational Environmental Satellites) spacecraft. Thus, we demonstrate and discuss the potential science capabilities of the MAGIC instrument onboard a CubeSat platform.
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Journal articleNilsson H, Wieser GS, Behar E, et al., 2015,
Evolution of the ion environment of comet 67P/Churyumov-Gerasimenko - Observations between 3.6 and 2.0 AU
, Astronomy & Astrophysics, Vol: 583, ISSN: 0004-6361Context. The Rosetta spacecraft is escorting comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 AU, wherethe comet activity was low, until perihelion at 1.24 AU. Initially, the solar wind permeates the thin comet atmosphere formed fromsublimation.Aims. Using the Rosetta Plasma Consortium Ion Composition Analyzer (RPC-ICA), we study the gradual evolution of the comet ionenvironment, from the first detectable traces of water ions to the stage where cometary water ions accelerated to about 1 keV energyare abundant. We compare ion fluxes of solar wind and cometary origin.Methods. RPC-ICA is an ion mass spectrometer measuring ions of solar wind and cometary origins in the 10 eV–40 keV energyrange.Results. We show how the flux of accelerated water ions with energies above 120 eV increases between 3.6 and 2.0 AU. The 24 haverage increases by 4 orders of magnitude, mainly because high-flux periods become more common. The water ion energy spectraalso become broader with time. This may indicate a larger and more uniform source region. At 2.0 AU the accelerated water ion fluxis frequently of the same order as the solar wind proton flux. Water ions of 120 eV–few keV energy may thus constitute a significantpart of the ions sputtering the nucleus surface. The ion density and mass in the comet vicinity is dominated by ions of cometary origin.The solar wind is deflected and the energy spectra broadened compared to an undisturbed solar wind.Conclusions. The flux of accelerated water ions moving from the upstream direction back toward the nucleus is a strongly nonlinearfunction of the heliocentric distance.
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Journal articleCarr CM, Edberg NJT, Eriksson AI, et al., 2015,
Spatial distribution of low-energy plasma around 2 comet 67P/CG from Rosetta measurements
, Geophysical Research Letters, Vol: 42, Pages: 4263-4269, ISSN: 1944-8007We use measurements from the Rosetta plasma consortium Langmuir probe and mutual impedance probe to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e., the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be ∼1–2·10−6, at a cometocentric distance of 10 km and at 3.1 AU from the Sun. A clear 6.2 h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisionless plasma within 260 km from the nucleus falls off with radial distance as ∼1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet.
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Journal articleCeppi P, Hartmann DL, 2015,
Connections between clouds, radiation, and midlatitude dynamics: a review
, Current Climate Change Reports, Vol: 1, Pages: 94-102, ISSN: 2198-6061We review the effects of dynamical variability on clouds and radiation in observations and models and discuss their implications for cloud feedbacks. Jet shifts produce robust meridional dipoles in upper-level clouds and longwave cloud-radiative effect (CRE), but low-level clouds, which do not simply shift with the jet, dominate the shortwave CRE. Because the effect of jet variability on CRE is relatively small, future poleward jet shifts with global warming are only a second-order contribution to the total CRE changes around the midlatitudes, suggesting a dominant role for thermodynamic effects. This implies that constraining the dynamical response is unlikely to reduce the uncertainty in extratropical cloud feedback. However, we argue that uncertainty in the cloud-radiative response does affect the atmospheric circulation response to global warming, by modulating patterns of diabatic forcing. How cloud feedbacks can affect the dynamical response to global warming is an important topic of future research.
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Journal articleMangeon T, Field R, Fromm M, et al., 2015,
Satellite versus ground-based estimates of burned area: a comparison between MODIS based burned area and fire agency reports over North America in 2007
, The Anthropocene Review, Vol: 3, Pages: 76-92, ISSN: 2053-0196North American wildfire management teams routinely assess burned area on site during firefighting campaigns; meanwhile, satellite observations provide systematic and global burned-area data. Here we compare satellite and ground-based daily burned area for wildfire events for selected large fires across North America in 2007 on daily timescales. In a sample of 26 fires across North America, we found the Global Fire Emissions Database Version 4 (GFED4) estimated about 80% of the burned area logged in ground-based Incident Status Summary (ICS-209) over 8-day analysis windows. Linear regression analysis found a slope between GFED and ICS-209 of 0.67 (with R = 0.96). The agreement between these data sets was found to degrade at short timescales (from R = 0.81 for 4-day to R = 0.55 for 2-day). Furthermore, during large burning days (> 3000 ha) GFED4 typically estimates half of the burned area logged in the ICS-209 estimates.
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Journal articleCargill PJ, Warren HP, Bradshaw SJ, 2015,
Modelling nanoflares in active regions and implications for coronal heating mechanisms
, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 373, ISSN: 1364-503X- Author Web Link
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- Citations: 46
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Journal articleVoulgarakis A, Field RD, 2015,
Fire influences on atmospheric composition, air quality, and climate
, Current Pollution Reports, Vol: 1, Pages: 70-81, ISSN: 2198-6592Fires impact atmospheric composition through their emissions, which range from long-lived gases to short-lived gases and aerosols. Effects are typically larger in the tropics and boreal regions but can also be substantial in highly populated areas in the northern mid-latitudes. In all regions, fire can impact air quality and health. Similarly, its effect on large-scale atmospheric processes, including regional and global atmospheric chemistry and climate forcing, can be substantial, but this remains largely unexplored. The impacts are primarily realised in the boundary layer and lower free troposphere but can also be noticeable in upper troposphere/lower stratosphere (UT/LS) region, for the most intense fires. In this review, we summarise the recent literature on findings related to fire impact on atmospheric composition, air quality and climate. We explore both observational and modelling approaches and present information on key regions and on the globe as a whole. We also discuss the current and future directions in this area of research, focusing on the major advances in emission estimates, the emerging efforts to include fire as a component in Earth system modelling and the use of modelling to assess health impacts of fire emissions.
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Journal articleDunlop MW, Yang J-Y, Yang Y-Y, et al., 2015,
Simultaneous field-aligned currents at Swarm and Cluster satellites
, Geophysical Research Letters, Vol: 42, Pages: 3683-3691, ISSN: 1944-8007We show for the first time, with direct, multispacecraft calculations of electric current density, and other methods, matched signatures of field-aligned currents (FACs) sampled simultaneously near the ionosphere at low (~500 km altitude) orbit and in the magnetosphere at medium (~2.5 RE altitude) orbits using a particular Swarm and Cluster conjunction. The Cluster signatures are interpreted and ordered through joint mapping of the ground/magnetospheric footprints and estimation of the auroral zone boundaries (taken as indication of the boundaries of Region 1 and Region 2 currents). We find clear evidence of both small-scale and large-scale FACs and clear matching of the behavior and structure of the large-scale currents at both Cluster and Swarm. The methodology is made possible through the joint operations of Cluster and Swarm, which contain, in the first several months of Swarm operations, a number of close three-spacecraft configurations.
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Journal articleCarr CM, Erikksson S, Lapenta G, et al., 2015,
On Multiple Reconnection X-lines and Tripolar Perturbations of Strong Guide Magnetic Fields
, The Astrophysical Journal, Vol: 805, ISSN: 0004-637XWe 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,
What frequencies of standing surface waves can the subsolar magnetopause support?
, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 3632-3646, ISSN: 2169-9380It 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‐called Kruskal‐Schwarzschild (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‐of‐flight 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,
SOLAR WIND TURBULENCE FROM MHD TO SUB-ION SCALES: HIGH-RESOLUTION HYBRID SIMULATIONS
, Astrophysical Journal Letters, Vol: 804, ISSN: 2041-8213We 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,
EFFECTS OF ELECTRON DRIFTS ON THE COLLISIONLESS DAMPING OF KINETIC ALFVEN WAVES IN THE SOLAR WIND
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 804, ISSN: 2041-8205- Author Web Link
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- Citations: 12
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Journal articleFletcher L, Cargill PJ, Antiochos SK, et al., 2015,
Structures in the Outer Solar Atmosphere
, SPACE SCIENCE REVIEWS, Vol: 188, Pages: 211-249, ISSN: 0038-6308- Author Web Link
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- Citations: 19
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Journal articleCzaja A, Marshall J, 2015,
Why is there net surface heating over the Antarctic Circumpolar Current?
, OCEAN DYNAMICS, Vol: 65, Pages: 751-760, ISSN: 1616-7341- Author Web Link
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- Citations: 7
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Journal articleHu F, Sun J, Brindley HE, et al., 2015,
Systems Analysis for Thermal Infrared '<i>THz Torch</i>' Applications
, JOURNAL OF INFRARED MILLIMETER AND TERAHERTZ WAVES, Vol: 36, Pages: 474-495, ISSN: 1866-6892- Author Web Link
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- Citations: 12
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Journal articleBalogh A, Bykov A, Eastwood J, et al., 2015,
Multi-scale Structure Formation and Dynamics in Cosmic Plasmas
, SPACE SCIENCE REVIEWS, Vol: 188, Pages: 1-2, ISSN: 0038-6308 -
Journal articleEastwood JP, Hietala H, Toth G, et al., 2015,
What Controls the Structure and Dynamics of Earth's Magnetosphere?
, SPACE SCIENCE REVIEWS, Vol: 188, Pages: 251-286, ISSN: 0038-6308- Author Web Link
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- Citations: 49
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Journal articleHeiter U, Lind K, Asplund M, et al., 2015,
Atomic and molecular data for optical stellar spectroscopy
, PHYSICA SCRIPTA, Vol: 90, ISSN: 0031-8949- Cite
- Citations: 132
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Journal articleHartinger MD, Plaschke F, Archer MO, et al., 2015,
The global structure and time evolution of dayside magnetopause surface eigenmodes
, GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 2594-2602, ISSN: 0094-8276- Author Web Link
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- Citations: 35
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Journal articleMasters A, 2015,
The dayside reconnection voltage applied to Saturn's magnetosphere
, GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 2577-2585, ISSN: 0094-8276- Author Web Link
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- Citations: 20
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Journal articleWang L, Yang L, He J, et al., 2015,
SOLAR WIND ∼20-200 keV SUPERHALO ELECTRONS AT QUIET TIMES
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 803, ISSN: 2041-8205- Author Web Link
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- Citations: 41
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Journal articleJackman CM, Thomsen MF, Mitchell DG, et al., 2015,
Field dipolarization in Saturn's magnetotail with planetward ion flows and energetic particle flow bursts: Evidence of quasi-steady reconnection
, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 3603-3617, ISSN: 2169-9402We 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,
XUV-driven mass loss from extrasolar giant planets orbiting active stars
, Icarus, Vol: 250, Pages: 357-367, ISSN: 1090-2643Upper 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,
INFERRING THE STRUCTURE OF THE SOLAR CORONA AND INNER HELIOSPHERE DURING THE MAUNDER MINIMUM USING GLOBAL THERMODYNAMIC MAGNETOHYDRODYNAMIC SIMULATIONS
, ASTROPHYSICAL JOURNAL, Vol: 802, ISSN: 0004-637X- Author Web Link
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- Citations: 63
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Journal articlePisa D, Hospodarsky GB, Kurth WS, et al., 2015,
Statistics of Langmuir wave amplitudes observed inside Saturn's foreshock by the Cassini spacecraft
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 120, Pages: 2531-2542, ISSN: 2169-9380- Author Web Link
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- Citations: 8
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Journal articleYates JN, Southwood DJ, Dougherty MK, 2015,
Magnetic phase structure of Saturn's 10.7h oscillations
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 120, Pages: 2631-2648, ISSN: 2169-9380- Author Web Link
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- Citations: 6
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Journal articleDelamere PA, Bagenal F, Paranicas C, et al., 2015,
Solar Wind and Internally Driven Dynamics: Influences on Magnetodiscs and Auroral Responses
, SPACE SCIENCE REVIEWS, Vol: 187, Pages: 51-97, ISSN: 0038-6308- Cite
- Citations: 51
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