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Journal articleGryspeerdt E, Stier P, White BA, et al., 2015, , Atmospheric Chemistry and Physics, Vol: 15, Pages: 7557-7570, ISSN: 1680-7324
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Journal articleGood SW, Forsyth RJ, Raines JM, et al., 2015, , Astrophysical Journal, Vol: 807, Pages: 177-189, ISSN: 1538-4357
The Solar Orbiter and Solar Probe Plus missions will provide observations of magnetic clouds closer to the Sunthan ever before, and it will be good preparation for these missions to make full use of the most recent in situ datasets from the inner heliosphere—namely, those provided by MErcury Surface, Space ENvironment, GEochemistry,and Ranging (MESSENGER) and Venus Express—for magnetic cloud studies. We present observations of thesame magnetic cloud made by MESSENGER at Mercury and later by Solar TErrestrial RElations Observatory-B(STEREO-B), while the spacecraft were radially aligned in 2011 November. Few such radial observations ofmagnetic clouds have been previously reported. Estimates of the solar wind speed at MESSENGER are alsopresented, calculated through the application of a previously established technique. The cloud宎s flux rope has beenanalyzed using force-free fitting; the rope diameter increased from 0.18 to 0.41 AU (corresponding to an rH0.94dependence on heliocentric distance, rH), and the axial magnetic field strength dropped from 46.0 to 8.7 nT (an -rH1.84 dependence) between the spacecraft, clear indications of an expanding structure. The axial magnetic flux was∼0.50 nT AU2 at both spacecraft, suggesting that the rope underwent no significant erosion through magneticreconnection between MESSENGER and STEREO-B. Further, we estimate the change in the cloud宎s angular widthby assuming helicity conservation. It has also been found that the rope axis rotated by 30° between the spacecraftto lie close to the solar equatorial plane at STEREO-B. Such a rotation, if it is a common feature of coronal massejection propagation, would have important implications for space weather forecasting.
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Journal articleCampagnola S, Boutonnet A, Martens W, et al., 2015, , IEEE Aerospace and Electronic Systems Magazine, Vol: 30, Pages: 6-17, ISSN: 0885-8985
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Journal articleMessori G, Czaja A, 2015, , QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Vol: 141, Pages: 2376-2389, ISSN: 0035-9009
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- Citations: 9
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Journal articleLavvas P, Yelle RV, Heays AN, et al., 2015, , Icarus, Vol: 260, Pages: 29-59, ISSN: 1090-2643
We present a detailed model for the vibrational population of all non pre-dissociating excited electronic states of N2, as well as for the ground and ionic states, in Titan’s atmosphere. Our model includes the detailed energy deposition calculations presented in the past (Lavvas, P. et al. [2011]. Icarus 213(1), 233–251) as well as the more recent developments in the high resolution N2 photo-absorption cross sections that allow us to calculate photo-excitation rates for different vibrational levels of singlet nitrogen states, and provide information for their pre-dissociation yields. In addition, we consider the effect of collisions and chemical reactions in the population of the different states. Our results demonstrate that above 600 km altitude, collisional processes are efficient only for a small sub-set of the excited states limited to the A and W(ν = 0) triplet states, and to a smaller degree to the a′ singlet state. In addition, we find that a significant population of vibrationally excited ground state N2 survives in Titan’s upper atmosphere. Our calculations demonstrate that this hot N2 population can improve the agreement between models and observations for the emission of the View the MathML source state that is significantly affected by resonant scattering. Moreover we discuss the potential implications of the vibrationally excited population on the ionospheric densities.
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Journal articleSagnieres LBM, Galand MIF, Cui J, et al., 2015, , Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 5899-5921, ISSN: 2169-9402
Titan has the most chemically complex ionosphere of the Solar System. The main sources of ions on the dayside are ionization by EUV solar radiation and on the nightside include ionization by precipitated electrons from Saturn's magnetosphere and transport of ions from the dayside, but many questions remain open. How well do models predict local ionization rates? How strongly do the ionization processes drive the ionospheric densities locally? To address these questions, we have carried out an analysis of ion densities from the Ion and Neutral Mass Spectrometer (INMS) from 16 close flybys of Titan's upper atmosphere. Using a simple chemical model applied to the INMS dataset, we have calculated the ion production rates and local ionization frequencies associated with primary ions inline image and inline image. We find that on the dayside the solar energy deposition model overestimates the INMS-derived inline image production rates by a factor of 2. On the nightside, however, the model driven by suprathermal electron intensities from the Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) sometimes agrees, other times underestimates the INMS-derived inline image production rates by a factor of up to 2-3. We find that below 1200 km, all ion number densities correlate with the local ionization frequency, although the correlation is significantly stronger for short-lived ions than long-lived ions. Furthermore, we find that for a given N2 local ionization frequency inline image has higher densities on the day-side than on the nightside. We explain that this is due to inline image being more efficiently ionized by solar photons than by magnetospheric electrons for a given amount of N2 ionization.
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BookHaigh JD, Cargill P, 2015,
The Sun's Influence on Climate
, ISBN: 9780691153841"--Peter Pilewskie, University of Colorado Boulder "This succinct volume will be invaluable to scientists and general readers who want to learn more about the Sun and its effects on our climate system.
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Journal articleHoraites K, Boldyrev S, Krasheninnikov SI, et al., 2015, , PHYSICAL REVIEW LETTERS, Vol: 114, ISSN: 0031-9007
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- Citations: 17
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Journal articleLucas DD, Kwok CY, Cameron-Smith P, et al., 2015, , Geoscientific Instrumentation, Methods and Data Systems, Vol: 4, Pages: 121-137, ISSN: 2193-0864
Emission 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, , GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 4, Pages: 705-749, ISSN: 2193-0856
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Journal articleHorbury TS, Archer MO, Brown P, et al., 2015, , Annales Geophysicae, Vol: 33, Pages: 725-735, ISSN: 1432-0576
We present the first in-flight results from a novel miniaturised anisotropic magnetoresistive space magnetometer, MAGIC (MAGnetometer from 51勛圖厙 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, , Astronomy & Astrophysics, Vol: 583, ISSN: 0004-6361
Context. 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, , Geophysical Research Letters, Vol: 42, Pages: 4263-4269, ISSN: 1944-8007
We 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, , Current Climate Change Reports, Vol: 1, Pages: 94-102, ISSN: 2198-6061
We 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, , The Anthropocene Review, Vol: 3, Pages: 76-92, ISSN: 2053-0196
North 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, , PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 373, ISSN: 1364-503X
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- Citations: 46
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Journal articleVoulgarakis A, Field RD, 2015, , Current Pollution Reports, Vol: 1, Pages: 70-81, ISSN: 2198-6592
Fires 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, , Geophysical Research Letters, Vol: 42, Pages: 3683-3691, ISSN: 1944-8007
We 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, , 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 socalled KruskalSchwarzschild (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 timeofflight 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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