Publications

Jackman CM, Thomsen MF, Mitchell DG, Sergis N, Arridge CS, Felici M, Badman SV, Paranicas C, Jia X, Hospodarksy GB, Andriopoulou M, Khurana KK, Smith AW, Dougherty MKet 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: 2169-9402

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 article

Chadney, Galand M, Unruh YC, Koskinen TT, Sanz-Forcada Jet al., 2015,

XUV-driven mass loss from extrasolar giant planets orbiting active stars

, 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).

Journal article

Riley P, Lionello R, Linker JA, Cliver E, Balogh A, Beer J, Charbonneau P, Crooker N, DeRosa M, Lockwood M, Owens M, McCracken K, Usoskin I, Koutchmy Set 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

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Citations: 63

Journal article

Pisa D, Hospodarsky GB, Kurth WS, Santolik O, Soucek J, Gurnett DA, Masters A, Hill MEet 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

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Citations: 8

Journal article

Yates 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

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Citations: 6

Journal article

Delamere PA, Bagenal F, Paranicas C, Masters A, Radioti A, Bonfond B, Ray L, Jia X, Nichols J, Arridge Cet 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

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Citations: 51

Journal article

Fox C, Green PD, Pickering JC, Humpage Net al., 2015,

Analysis of far-infrared spectral radiance observations of the water vapor continuum in the Arctic

, JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, Vol: 155, Pages: 57-65, ISSN: 0022-4073

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Citations: 9

Journal article

Kimura T, Badman SV, Tao C, Yoshioka K, Murakami G, Yamazaki A, Tsuchiya F, Bonfond B, Steffl AJ, Masters A, Kasahara S, Hasegawa H, Yoshikawa I, Fujimoto M, Clarke JTet al., 2015,

Transient internally driven aurora at Jupiter discovered by Hisaki and the Hubble Space Telescope

, GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 1662-1668, ISSN: 0094-8276

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Citations: 57

Journal article

Cui J, Galand M, Yelle RV, Wei Y, Zhang S-Jet al., 2015,

Day-to-night transport in the Martian ionosphere: Implications from total electron content measurements

, 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 article

Matteini L, Horbury TS, Pantellini F, Velli M, Schwartz SJet al., 2015,

Ion kinetic energy conservation and magnetic field strength constancy in multi-fluid solar wind alfvénic turbulence

, 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 article

Gingell PW, Burgess D, Matteini L, 2015,

THE THREE-DIMENSIONAL EVOLUTION OF ION-SCALE CURRENT SHEETS: TEARING AND DRIFT-KINK INSTABILITIES IN THE PRESENCE OF PROTON TEMPERATURE ANISOTROPY

, ASTROPHYSICAL JOURNAL, Vol: 802, ISSN: 0004-637X

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Citations: 20

Journal article

Martinez-Oliveros JC, Raftery C, Bain H, Liu Y, Pulupa M, Saint-Hilaire P, Higgins P, Krupar V, Krucker S, Bale SDet al., 2015,

STEREO-<i>Wind</i> Radio Positioning of an Unusually Slow Drifting Event

, SOLAR PHYSICS, Vol: 290, Pages: 891-901, ISSN: 0038-0938

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Citations: 5

Journal article

Nazarenko L, Schmidt GA, Miller RL, Tausnev N, Kelley M, Ruedy R, Russell GL, Aleinov I, Bauer M, Bauer S, Bleck R, Canuto V, Cheng Y, Clune TL, Del Genio AD, Faluvegi G, Hansen JE, Healy RJ, Kiang NY, Koch D, Lacis AA, LeGrande AN, Lerner J, Lo KK, Menon S, Oinas V, Perlwitz J, Puma MJ, Rind D, Romanou A, Sato M, Shindell DT, Sun S, Tsigaridis K, Unger N, Voulgarakis A, Yao M-S, Zhang Jet al., 2015,

Future climate change under RCP emission scenarios with GISS ModelE2

, JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS, Vol: 7, Pages: 244-267

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Citations: 117

Journal article

Cui J, Galand M, Zhang SJ, Vigren E, Zou Het al., 2015,

The electron thermal structure in the dayside Martian ionosphere implied by the MGS radio occultation data

, 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 paper

Pickering JC, Fox C, Murray JE, Last Aet 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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Citations: 1

Journal article

Goldberg SJ, Ball GI, Allen BC, Schladow SG, Simpson AJ, Masoom H, Soong R, Graven HD, Aluwihare LIet al., 2015,

Refractory dissolved organic nitrogen accumulation in high-elevation lakes

, 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 paper

Pickering JC, Fox C, Murray JE, Last Aet 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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Citations: 1

Conference paper

Pickering JC, Mushtaq S, Steers EBM, Weiss Zet 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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Citations: 3

Conference paper

Pickering JC, Mushtaq S, Steers EBM, Weiss Zet 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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Book chapter

Southwood 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

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Journal article

Brindley H, Bantges R, Russell J, Murray J, Dancel C, Belotti C, Harries Jet al., 2015,

Spectral Signatures of Earth's Climate Variability over 5 Years from IASI

, JOURNAL OF CLIMATE, Vol: 28, Pages: 1649-1660, ISSN: 0894-8755

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Citations: 15

Journal article

Eastwood JP, Goldman MV, Hietala H, Newman DL, Mistry R, Lapenta Get al., 2015,

Ion reflection and acceleration near magnetotail dipolarization fronts associated with magnetic reconnection

, 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 article

Bertucci C, Hamilton DC, Kurth WS, Hospodarsky G, Mitchell D, Sergis N, Edberg NJT, Dougherty MKet al., 2015,

Titan's interaction with the supersonic solar wind

, GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 193-200, ISSN: 0094-8276

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Citations: 42

Journal article

Nilsson H, Wieser GS, Behar E, Wedlund CS, Gunell H, Yamauchi M, Lundin R, Barabash S, Wieser M, Carr C, Cupido E, Burch JL, Fedorov A, Sauvaud J-A, Koskinen H, Kallio E, Lebreton J-P, Eriksson A, Edberg N, Goldstein R, Henri P, Koenders C, Mokashi P, Nemeth Z, Richter I, Szego K, Volwerk M, Vallat C, Rubin Met al., 2015,

Birth of a comet magnetosphere: A spring of water ions

, 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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The cirrus coupled cloud-radiation experiment: CIRCCREX

High resolution FTS studies of the effects of trace molecular gases on Glow Discharge spectra and industrial applications

Formation of Magnetotails: Fast and Slow Rotators Compared

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