Publications

Journal article

Plaschke F, Goetz C, Volwerk M, Richter I, Fruehauff D, Narita Y, Glassmeier K-H, Dougherty MKet al., 2017,

Fluxgate magnetometer offset vector determination by the 3D mirror mode method

, Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S675-S684, ISSN: 0035-8711

Fluxgate magnetometers on-board spacecraft need to be regularly calibrated in flight. In low fields, the most important calibration parameters are the three offset vector components, which represent the magnetometer measurements in vanishing ambient magnetic fields. In case of three-axis stabilized spacecraft, a few methods exist to determine offsets: (i) by analysis of Alfvénic fluctuations present in the pristine interplanetary magnetic field, (ii) by rolling the spacecraft around at least two axes, (iii) by cross-calibration against measurements from electron drift instruments or absolute magnetometers, and (iv) by taking measurements in regions of well-known magnetic fields, e.g. cometary diamagnetic cavities. In this paper, we introduce a fifth option, the 3-dimensional (3D) mirror mode method, by which 3D offset vectors can be determined using magnetic field measurements of highly compressional waves, e.g. mirror modes in the Earth’s magnetosheath. We test the method by applying it to magnetic field data measured by the following: the Time History of Events and Macroscale Interactions during Substorms-C spacecraft in the terrestrial magnetosheath, the Cassini spacecraft in the Jovian magnetosheath and the Rosetta spacecraft in the vicinity of comet 67P/Churyumov–Gerasimenko. The tests reveal that the achievable offset accuracies depend on the ambient magnetic field strength (lower strength meaning higher accuracy), on the length of the underlying data interval (more data meaning higher accuracy) and on the stability of the offset that is to be determined.

Journal article

Keeling RF, Graven HD, Welp LR, Resplandy L, Bi J, Piper SC, Sun Y, Bollenbacher A, Meijer HAJet al., 2017,

Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis

, Proceedings of the National Academy of Sciences of the United States of America, Vol: 114, Pages: 10361-10366, ISSN: 0027-8424

A decrease in the 13C/12C ratio of atmospheric CO2 has been documented by direct observations since 1978 and from ice core measurements since the industrial revolution. This decrease, known as the 13C-Suess effect, is driven primarily by the input of fossil fuel-derived CO2 but is also sensitive to land and ocean carbon cycling and uptake. Using updated records, we show that no plausible combination of sources and sinks of CO2 from fossil fuel, land, and oceans can explain the observed 13C-Suess effect unless an increase has occurred in the 13C/12C isotopic discrimination of land photosynthesis. A trend toward greater discrimination under higher CO2 levels is broadly consistent with tree ring studies over the past century, with field and chamber experiments, and with geological records of C3 plants at times of altered atmospheric CO2, but increasing discrimination has not previously been included in studies of long-term atmospheric 13C/12C measurements. We further show that the inferred discrimination increase of 0.014 ± 0.007‰ ppm−1 is largely explained by photorespiratory and mesophyll effects. This result implies that, at the global scale, land plants have regulated their stomatal conductance so as to allow the CO2 partial pressure within stomatal cavities and their intrinsic water use efficiency to increase in nearly constant proportion to the rise in atmospheric CO2 concentration.

Journal article

Saunois M, Bousquet P, Poulter B, Peregon A, Ciais P, Canadell JG, Dlugokencky EJ, Etiope G, Bastviken D, Houweling S, Janssens-Maenhout G, Tubiello FN, Castaldi S, Jackson RB, Alexe M, Arora VK, Beerling DJ, Bergamaschi P, Blake DR, Brailsford G, Bruhwiler L, Crevoisier C, Crill P, Covey K, Frankenberg C, Gedney N, Hoeglund-Isaksson L, Ishizawa M, Ito A, Joos F, Kim H-S, Kleinen T, Krummel P, Lamarque J-F, Langenfelds R, Locatelli R, Machida T, Maksyutov S, Melton JR, Morino I, Naik V, O'Doherty S, Parmentier F-J, Patra PK, Peng C, Peng S, Peters GP, Pison I, Prinn R, Ramonet M, Riley WJ, Saito M, Santini M, Schroeder R, Simpson IJ, Spahni R, Takizawa A, Thornton BF, Tian H, Tohjima Y, Viovy N, Voulgarakis A, Weiss R, Wilton DJ, Wiltshire A, Worthy D, Wunch D, Xu X, Yoshida Y, Zhang B, Zhang Z, Zhu Qet al., 2017,

Variability and quasi-decadal changes in the methane budget over the period 2000-2012

, Atmospheric Chemistry and Physics, Vol: 17, Pages: 11135-11161, ISSN: 1680-7316

Following the recent Global Carbon Project (GCP) synthesis of the decadal methane (CH4) budget over 2000–2012 (Saunois et al., 2016), we analyse here the same dataset with a focus on quasi-decadal and inter-annual variability in CH4 emissions. The GCP dataset integrates results from top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models (including process-based models for estimating land surface emissions and atmospheric chemistry), inventories of anthropogenic emissions, and data-driven approaches. The annual global methane emissions from top-down studies, which by construction match the observed methane growth rate within their uncertainties, all show an increase in total methane emissions over the period 2000–2012, but this increase is not linear over the 13 years. Despite differences between individual studies, the mean emission anomaly of the top-down ensemble shows no significant trend in total methane emissions over the period 2000–2006, during the plateau of atmospheric methane mole fractions, and also over the period 2008–2012, during the renewed atmospheric methane increase. However, the top-down ensemble mean produces an emission shift between 2006 and 2008, leading to 22 [16–32] Tg CH4 yr−1 higher methane emissions over the period 2008–2012 compared to 2002–2006. This emission increase mostly originated from the tropics, with a smaller contribution from mid-latitudes and no significant change from boreal regions. The regional contributions remain uncertain in top-down studies. Tropical South America and South and East Asia seem to contribute the most to the emission increase in the tropics. However, these two regions have only limited atmospheric measurements and remain therefore poorly constrained. The sectorial partitioning of this emission increase between the periods 2002–2006 and 2008–2012 differs from one atmospheric in

Journal article

Mendillo M, Narvaez C, Vogt MF, Mayyasi M, Forbes J, Galand M, Thiemann E, Benna M, Eparvier F, Chamberlin P, Mahaffy P, Andersson Let al., 2017,

Sources of ionospheric variability at Mars

, Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 9670-9684, ISSN: 2169-9380

During the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission's deep-dip #2 campaign of 17–22 April 2015, spacecraft instruments observed all of the physical parameters needed to assess the photo-chemical-equilibrium (PCE) explanation for ionospheric variability at a fixed altitude (135 km) near the peak of the Martian ionosphere. MAVEN measurements of electron density, electron temperature, neutral CO2 density, and solar irradiance were collected during 28 orbits. When inserted into the PCE equation, the measurements of varying PCE drivers correlated with the observed electron density variations to within instrumental uncertainty levels. The dominant source of this positive correlation was the variability of CO2 densities associated with the longitudinal wave-2 component of nonmigrating tides in the Martian thermosphere.

Journal article

Nakamura R, Nagai T, Birn J, Sergeev VA, Le Contel O, Varsani A, Baumjohann W, Nakamura T, Apatenkov S, Artemyev A, Ergun RE, Fuselier SA, Gershman DJ, Giles BJ, Khotyaintsev YV, Lindqvist P-A, Magnes W, Mauk B, Russell CT, Singer HJ, Stawarz J, Strangeway RJ, Anderson B, Bromund KR, Fischer D, Kepko L, Le G, Plaschke F, Slavin JA, Cohen I, Jaynes A, Turner DLet al., 2017,

Near-Earth plasma sheet boundary dynamics during substorm dipolarization

, Earth, Planets and Space, Vol: 69, ISSN: 1880-5981

We report on the large-scale evolution of dipolarization in the near-Earth plasma sheet during an intense (AL ~ −1000 nT) substorm on August 10, 2016, when multiple spacecraft at radial distances between 4 and 15 R E were present in the night-side magnetosphere. This global dipolarization consisted of multiple short-timescale (a couple of minutes) B z disturbances detected by spacecraft distributed over 9 MLT, consistent with the large-scale substorm current wedge observed by ground-based magnetometers. The four spacecraft of the Magnetospheric Multiscale were located in the southern hemisphere plasma sheet and observed fast flow disturbances associated with this dipolarization. The high-time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and flow disturbances separately. A distinct pattern of the flow and field disturbance near the plasma boundaries was found. We suggest that a vortex motion created around the localized flows resulted in another field-aligned current system at the off-equatorial side of the BBF-associated R1/R2 systems, as was predicted by the MHD simulation of a localized reconnection jet. The observations by GOES and Geotail, which were located in the opposite hemisphere and local time, support this view. We demonstrate that the processes of both Earthward flow braking and of accumulated magnetic flux evolving tailward also control the dynamics in the boundary region of the near-Earth plasma sheet.

Journal article

Yao ZH, Coates AJ, Ray LC, Rae IJ, Grodent D, Jones GH, Dougherty MK, Owen CJ, Guo RL, Dunn WR, Radioti A, Pu ZY, Lewis GR, Waite JH, Gerard J-Cet al., 2017,

Corotating Magnetic Reconnection Site in Saturn's Magnetosphere

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 846, ISSN: 2041-8205

Using measurements from theCassinispacecraft in Saturn’s magnetosphere, we propose a 3D physical picture of acorotating reconnection site, which can only be driven by an internally generated source. Our results demonstratethat the corotating magnetic reconnection can drive an expansion of the current sheet in Saturn’s magnetosphereand, consequently, can produce Fermi acceleration of electrons. This reconnection site lasted for longer than one ofSaturn’s rotation period. The long-lasting and corotating natures of the magnetic reconnection site at Saturnsuggest fundamentally different roles of magnetic reconnection in driving magnetospheric dynamics(e.g., theauroral precipitation)from the Earth. Our corotating reconnection picture could also potentially shed light on thefast rotating magnetized plasma environments in the solar system and beyond.

Journal article

Balogh A, von Steiger R, 2017,

Editorial: Measuring Solar Magnetic Fields-An Outline of History, Current Status and Challenges

, Space Science Reviews, Vol: 210, Pages: 1-3, ISSN: 0038-6308

Cite

Journal article

Nave G, Sansonetti CJ, Townley-Smith K, Pickering JC, Thorne AP, Liggins F, Clear Cet al., 2017,

Comprehensive atomic wavelengths, energy levels, and hyperfine structure for singly ionized iron-group elements

, CANADIAN JOURNAL OF PHYSICS, Vol: 95, Pages: 811-816, ISSN: 0008-4204

Journal article

Eriksson AI, Engelhardt IAD, Andre M, Bostrom R, Edberg NJT, Johansson FL, Odelstad E, Vigren E, Wahlund J-E, Henri P, Lebreton J-P, Miloch WJ, Paulsson JJP, Wedlund CS, Yang L, Karlsson T, Jarvinen R, Broiles T, Mandt K, Carr CM, Galand M, Nilsson H, Norberg Cet al., 2017,

Cold and warm electrons at comet 67P/Churyumov-Gerasimenko

, Astronomy and Astrophysics, Vol: 605, ISSN: 0004-6361

Context. Strong electron cooling on the neutral gas in cometary comae has been predicted for a long time, but actual measurements of low electron temperature are scarce.Aims. Our aim is to demonstrate the existence of cold electrons in the inner coma of comet 67P/Churyumov-Gerasimenko and show filamentation of this plasma.Methods. In situ measurements of plasma density, electron temperature and spacecraft potential were carried out by the Rosetta Langmuir probe instrument, LAP. We also performed analytical modelling of the expanding two-temperature electron gas.Results. LAP data acquired within a few hundred km from the nucleus are dominated by a warm component with electron temperature typically 5–10 eV at all heliocentric distances covered (1.25 to 3.83 AU). A cold component, with temperature no higher than about 0.1 eV, appears in the data as short (few to few tens of seconds) pulses of high probe current, indicating local enhancement of plasma density as well as a decrease in electron temperature. These pulses first appeared around 3 AU and were seen for longer periods close to perihelion. The general pattern of pulse appearance follows that of neutral gas and plasma density. We have not identified any periods with only cold electrons present. The electron flux to Rosetta was always dominated by higher energies, driving the spacecraft potential to order − 10 V.Conclusions. The warm (5–10 eV) electron population observed throughout the mission is interpreted as electrons retaining the energy they obtained when released in the ionisation process. The sometimes observed cold populations with electron temperatures below 0.1 eV verify collisional cooling in the coma. The cold electrons were only observed together with the warm population. The general appearance of the cold population appears to be consistent with a Haser-like model, implicitly supporting also the coupling of ions to the neutral gas. The expanding cold plasma is unstable, forming fil

Journal article

Dougherty MK, 2017,

CASSINI-HUYGENS Saturn in the infrared

, NATURE ASTRONOMY, Vol: 1, Pages: 579-579, ISSN: 2397-3366

Journal article

Sun H, Guo J, Wu S, Liu F, Dong Ret al., 2017,

Development and validation of a simplified titration method for monitoring volatile fatty acids in anaerobic digestion

, Waste Management, Vol: 67, Pages: 43-50, ISSN: 0956-053X

Journal article

Liu TZ, Lu S, Angelopoulos V, Hietala H, Wilson LBet al., 2017,

Fermi acceleration of electrons inside foreshock transient cores

, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 9248-9263, ISSN: 2169-9380

Journal article

Limaye SS, Lebonnois S, Mahieux A, Paetzold M, Bougher S, Bruinsma S, Chamberlain S, Clancy RT, Gerard J-C, Gilli G, Grassi D, Haus R, Herrmann M, Imamura T, Kohler E, Krause P, Migliorini A, Montmessin F, Pere C, Persson M, Piccialli A, Rengel M, Rodin A, Sandor B, Sornig M, Svedhem H, Tellmann S, Tanga P, Vandaele AC, Widemann T, Wilson CF, Mueller-Wodarg I, Zasova Let al., 2017,

The thermal structure of the Venus atmosphere: Intercomparison of Venus Express and ground based observations of vertical temperature and density profiles

, ICARUS, Vol: 294, Pages: 124-155, ISSN: 0019-1035

Journal article

Johnston CD, Hood AW, Cargill PJ, De Moortel Iet al., 2017,

A new approach for modelling chromospheric evaporation in response to enhanced coronal heating

, Astronomy & Astrophysics, Vol: 605, Pages: A8-A8, ISSN: 0004-6361

We proposed that the use of an approximate “jump condition” at the solar transition region permits fast and accurate numerical solutions of the one dimensional hydrodynamic equations when the corona undergoes impulsive heating. In particular, it eliminates the need for the very short timesteps imposed by a highly resolved numerical grid. This paper presents further examples of the applicability of the method for cases of non-uniform heating, in particular, nanoflare trains (uniform in space but non-uniform in time) and spatially localised impulsive heating, including at the loop apex and base of the transition region. In all cases the overall behaviour of the coronal density and temperature shows good agreement with a fully resolved one dimensional model and is significantly better than the equivalent results from a 1D code run without using the jump condition but with the same coarse grid. A detailed assessment of the errors introduced by the jump condition is presented showing that the causes of discrepancy with the fully resolved code are (i) the neglect of the terms corresponding to the rate of change of total energy in the unresolved atmosphere; (ii) mass motions at the base of the transition region and (iii) for some cases with footpoint heating, an over-estimation of the radiative losses in the transition region.

Journal article

Bao M, Tan X, Hartmann DL, Ceppi Pet al., 2017,

Classifying the tropospheric precursor patterns of sudden stratospheric warmings

, Geophysical Research Letters, Vol: 44, Pages: 8011-8016, ISSN: 0094-8276

Classifying the tropospheric precursor patterns of sudden stratospheric warmings (SSWs) may provide insight into the different physical mechanisms of SSWs. Based on 37 major SSWs during the 1958–2014 winters in the ERA reanalysis data sets, the self‐organizing maps method is used to classify the tropospheric precursor patterns of SSWs. The cluster analysis indicates that one of the precursor patterns appears as a mixed pattern consisting of the negative‐signed Western Hemisphere circulation pattern and the positive phase of the Pacific‐North America pattern. The mixed pattern exhibits higher statistical significance as a precursor pattern of SSWs than other previously identified precursors such as the subpolar North Pacific low, Atlantic blocking, and the western Pacific pattern. Other clusters confirm northern European blocking and Gulf of Alaska blocking as precursors of SSWs. Linear interference with the climatological planetary waves provides a simple interpretation for the precursors. The relationship between the classified precursor patterns of SSWs and ENSO phases as well as the types of SSWs is discussed.

Journal article

Schutgens N, Tsyro S, Gryspeerdt E, Goto D, Weigum N, Schulz M, Stier Pet al., 2017,

On the spatio-temporal representativeness of observations

, Atmospheric Chemistry and Physics Discussions, Vol: 17, Pages: 9761-9780, ISSN: 1680-7367

The discontinuous spatio-temporal sampling ofobservations has an impact when using them to construct climatologiesor evaluate models. Here we provide estimates ofthis so-called representation error for a range of timescalesand length scales (semi-annually down to sub-daily, 300 to50 km) and show that even after substantial averaging of datasignificant representation errors may remain, larger than typicalmeasurement errors. Our study considers a variety ofobservations: ground-site or in situ remote sensing (PM2.5,black carbon mass or number concentrations), satellite remotesensing with imagers or lidar (extinction). We show thatobservational coverage (a measure of how dense the spatiotemporalsampling of the observations is) is not an effectivemetric to limit representation errors. Different strategiesto construct monthly gridded satellite L3 data are assessedand temporal averaging of spatially aggregated observations(super-observations) is found to be the best, although it stillallows for significant representation errors. However, temporalcollocation of data (possible when observations are comparedto model data or other observations), combined withtemporal averaging, can be very effective at reducing representationerrors. We also show that ground-based and wideswathimager satellite remote sensing data give rise to similarrepresentation errors, although their observational samplingis different. Finally, emission sources and orographycan lead to representation errors that are very hard to reduce,even with substantial temporal averaging.

Conference paper

Sulaiman AH, Masters A, Burgess D, Sergis N, Stawarz L, Fujimoto M, Coates AJ, Dougherty MKet al., 2017,

Cassini Observations of Saturn's High-Mach Number Bow Shock

, 32nd General Assembly and Scientific Symposium of the International-Union-of-Radio-Science (URSI GASS), Publisher: IEEE

Journal article

Eastwood J, Nakamura R, Turc L, Mejnertsen L, Hesse Met al., 2017,

The scientific foundations of forecasting magnetospheric space weather

, Space Science Reviews, Vol: 212, Pages: 1221-1252, ISSN: 1572-9672

The magnetosphere is the lens through which solar space weather phenomena are focused and directed towards the Earth. In particular, the non-linear interaction of the solar wind with the Earth’s magnetic field leads to the formation of highly inhomogenous electrical currents in the ionosphere which can ultimately result in damage to and problems with the operation of power distribution networks. Since electric power is the fundamental cornerstone of modern life, the interruption of power is the primary pathway by which space weather has impact on human activity and technology. Consequently, in the context of space weather, it is the ability to predict geomagnetic activity that is of key importance. This is usually stated in terms of geomagnetic storms, but we argue that in fact it is the substorm phenomenon which contains the crucial physics, and therefore prediction of substorm occurrence, severity and duration, either within the context of a longer-lasting geomagnetic storm, but potentially also as an isolated event, is of critical importance. Here we review the physics of the magnetosphere in the frame of space weather forecasting, focusing on recent results, current understanding, and an assessment of probable future developments.

Journal article

Stawarz JE, Eastwood JP, Varsani A, Ergun RE, Shay MA, Nakamura R, Phan TD, Burch JL, Gershman DJ, Giles BL, Goodrich KA, Khotyaintsev YV, Lindqvist P-A, Russell CT, Strangeway RJ, Torbert RBet al., 2017,

Magnetospheric Multiscale analysis of intense field-aligned Poynting flux near the Earth's plasma sheet boundary

, Geophysical Research Letters, Vol: 44, Pages: 7106-7113, ISSN: 1944-8007

The Magnetospheric Multiscale mission is employed to examine intense Poynting flux directed along the background magnetic field toward Earth, which reaches amplitudes of nearly 2 mW/m2. The event is located within the plasma sheet but likely near the boundary at a geocentric distance of 9 RE in association with bulk flow signatures. The fluctuations have wavelengths perpendicular to the magnetic field of 124–264 km (compared to an ion gyroradius of 280 km), consistent with highly kinetic Alfvén waves. While the wave vector remains highly perpendicular to the magnetic field, there is substantial variation of the direction in the perpendicular plane. The field-aligned Poynting flux may be associated with kinetic Alfvén waves released along the separatrix by magnetotail reconnection and/or the radiation of waves excited by bursty bulk flow braking and may provide a means through which energy released by magnetic reconnection is transferred to the auroral region.

Journal article

Muñoz V, Domínguez M, Valdivia JA, Good S, Nigro G, Carbone Vet al., 2017,

Evolution of fractality in magnetized plasmas

<jats:p>Abstract. We studied the temporal evolution of fractality for geomagnetic activity, by calculating fractal dimensions from Dst data and from an MHD shell model for a turbulent magnetized plasma, which may be a useful model to study geomagnetic activity under solar wind forcing. We show that the shell model is able to reproduce the relationship between the fractal dimension and the occurrence of dissipative events, but only in a certain region of viscosity and resistivity values. We also present preliminary results of the application of these ideas to the study of the magnetic field time series in the solar wind during magnetic clouds. Results suggest that the fractal dimension is able to characterize the complexity of the magnetic cloud structure. </jats:p>

Journal article

Øieroset M, Phan TD, Shay MA, Haggerty CC, Fujimoto M, Angelopoulos V, Eastwood JP, Mozer FSet al., 2017,

THEMIS multispacecraft observations of a reconnecting magnetosheath current sheet with symmetric boundary conditions and a large guide field

, Geophysical Research Letters, Vol: 44, Pages: 7598-7606, ISSN: 0094-8276

We report three spacecraft observations of a reconnecting magnetosheath current sheet with a guide field of unity, with THEMIS D (THD) and THEMIS E (THE)/THEMIS A (THA) observing oppositely directed reconnection exhausts, indicating the presence of an X line between the spacecraft. The near-constant convective speed of the magnetosheath current sheet allowed the direct translation of the observed time series into spatial profiles. THD observed asymmetries in the plasma density and temperature profiles across the exhaust, characteristics of symmetric reconnection with a guide field. The exhausts at THE and THA, on the other hand, were not the expected mirror image of the THD exhaust in terms of the plasma and field profiles. They consisted of a main outflow at the center of the current sheet, flanked by oppositely directed flows at the two edges of the current sheet, suggesting the presence of a second X line, whose outflow wraps around the outflow from the first X line.

Journal article

Witasse O, Sanchez-Cano B, Mays ML, Kajdic P, Opgenoorth H, Elliott HA, Richardson IG, Zouganelis I, Zender J, Wimmer-Schweingruber RF, Turc L, Taylor MGGT, Roussos E, Rouillard A, Richter I, Richardson JD, Ramstad R, Provan G, Posner A, Plaut JJ, Odstrcil D, Nilsson H, Niemenen P, Milan SE, Mandt K, Lohf H, Lester M, Lebreton J-P, Kuulkers E, Krupp N, Koenders C, James MK, Intzekara D, Holmstrom M, Hassler DM, Hall BES, Guo J, Goldstein R, Goetz C, Glassmeier KH, Genot V, Evans H, Espley J, Edberg NJT, Dougherty M, Cowley SWH, Burch J, Behar E, Barabash S, Andrews DJ, Altobelli Net al., 2017,

Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto: Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU

, Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 7865-7890, ISSN: 2169-9380

We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44 h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110–111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116°, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.

Journal article

Dudik J, Dzifcakova E, Meyer-Vernet N, Del Zanna G, Young PR, Giunta A, Sylwester B, Sylwester J, Oka M, Mason HE, Vocks C, Matteini L, Krucker S, Williams DR, Mackovjak Set al., 2017,

Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and SolarWind (Invited Review)

, SOLAR PHYSICS, Vol: 292, ISSN: 0038-0938

Journal article

Desai RT, Coates AJ, Wellbrock A, Vuitton V, Crary FJ, Gonzalez-Caniulef D, Shebanits O, Jones GH, Lewis GR, Waite JH, Cordiner M, Taylor SA, Kataria DO, Wahlund J-E, Edberg NJT, Sittler ECet al., 2017,

Carbon chain anions and the growth of complex organic molecules in titan's ionosphere

, Letters of the Astrophysical Journal, Vol: 844, ISSN: 2041-8205

Cassini discovered a plethora of neutral and ionized molecules in Titan's ionosphere including, surprisingly, anions and negatively charged molecules extending up to 13,800 u q−1. In this Letter, we forward model the Cassini electron spectrometer response function to this unexpected ionospheric component to achieve an increased mass resolving capability for negatively charged species observed at Titan altitudes of 950–1300 km. We report on detections consistently centered between 25.8 and 26.0 u q−1 and between 49.0–50.1 u q−1 which are identified as belonging to the carbon chain anions, CN−/C3N− and/or C2H−/C4H−, in agreement with chemical model predictions. At higher ionospheric altitudes, detections at 73–74 u q−1 could be attributed to the further carbon chain anions C5N−/C6H− but at lower altitudes and during further encounters extend over a higher mass/charge range. This, as well as further intermediary anions detected at >100 u, provide the first evidence for efficient anion chemistry in space involving structures other than linear chains. Furthermore, at altitudes below <1100 km, the low-mass anions (<150 u q−1) were found to deplete at a rate proportional to the growth of the larger molecules, a correlation that indicates the anions are tightly coupled to the growth process. This study adds Titan to an increasing list of astrophysical environments where chain anions have been observed and shows that anion chemistry plays a role in the formation of complex organics within a planetary atmosphere as well as in the interstellar medium.

Journal article

Moestl C, Isavnin A, Boakes PD, Kilpua EKJ, Davies JA, Harrison RA, Barnes D, Krupar V, Eastwood JP, Good SW, Forsyth RJ, Bothmer V, Reiss MA, Amerstorfer T, Winslow RM, Anderson BJ, Philpott LC, Rodriguez L, Rouillard AP, Gallagher P, Nieves-Chinchilla T, Zhang TLet al., 2017,

Modeling observations of solar coronal mass ejections with heliospheric imagers verified with the Heliophysics System Observatory

, Space Weather-the International Journal of Research and Applications, Vol: 15, Pages: 955-970, ISSN: 1539-4956

We present an advance toward accurately predicting the arrivals of coronal mass ejections (CMEs) at the terrestrial planets, including Earth. For the first time, we are able to assess a CME prediction model using data over two thirds of a solar cycle of observations with the Heliophysics System Observatory. We validate modeling results of 1337 CMEs observed with the Solar Terrestrial Relations Observatory (STEREO) heliospheric imagers (HI) (science data) from 8 years of observations by five in situ observing spacecraft. We use the self-similar expansion model for CME fronts assuming 60° longitudinal width, constant speed, and constant propagation direction. With these assumptions we find that 23%–35% of all CMEs that were predicted to hit a certain spacecraft lead to clear in situ signatures, so that for one correct prediction, two to three false alarms would have been issued. In addition, we find that the prediction accuracy does not degrade with the HI longitudinal separation from Earth. Predicted arrival times are on average within 2.6 ± 16.6 h difference of the in situ arrival time, similar to analytical and numerical modeling, and a true skill statistic of 0.21. We also discuss various factors that may improve the accuracy of space weather forecasting using wide-angle heliospheric imager observations. These results form a first-order approximated baseline of the prediction accuracy that is possible with HI and other methods used for data by an operational space weather mission at the Sun-Earth L5 point.

Journal article

Heritier KL, Altwegg K, Balsiger H, Berthelier J-J, Beth A, Bieler A, Biver N, Calmonte U, Combi MR, De Keyser J, Eriksson AI, Fiethe B, Fougere N, Fuselier SA, Galand M, Gasc S, Gombosi TI, Hansen KC, Hassig M, Kopp E, Odelstad E, Rubin M, Tzou C-Y, Vigren E, Vuitton Vet al., 2017,

Ion composition at comet 67P near perihelion: Rosetta observations and model-based interpretation

, Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S427-S442, ISSN: 0035-8711

We present the ion composition in the coma of comet 67P with newly detected ion species over the 28–37 u mass range, probed by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Double Focusing Mass Spectrometer (DFMS). In summer 2015, the nucleus reached its highest outgassing rate and ion-neutral reactions started to take place at low cometocentric distances. Minor neutrals can efficiently capture protons from the ion population, making the protonated version of these neutrals a major ion species. So far, onlyNH+4has been reported at comet 67P. However, there are additional neutral species with proton affinities higher than that of water (besides NH3) that have been detected in the coma of comet 67P: CH3OH, HCN, H2CO and H2S. Their protonated versions have all been detected. Statistics showing the number of detections with respect to the number of scans are presented. The effect of the negative spacecraft potential probed by the Rosetta Plasma Consortium/LAngmuir Probe on ion detection is assessed. An ionospheric model has been developed to assess the different ion density profiles and compare them to the ROSINA/DFMS measurements. It is also used to interpret the ROSINA/DFMS observations when different ion species have similar masses, and their respective densities are not high enough to disentangle them using the ROSINA/DFMS high-resolution mode. The different ion species that have been reported in the coma of 67P are summarized and compared with the ions detected at comet 1P/Halley during the Giotto mission.

Journal article

Pitna A, Safrankova J, Nemecek Z, Franci Let al., 2017,

Decay of Solar Wind Turbulence behind Interplanetary Shocks

, ASTROPHYSICAL JOURNAL, Vol: 844, ISSN: 0004-637X

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Conference paper

Owens MJ, Riley P, Horbury T, 2017,

The Role of Empirical Space-Weather Models (in a World of Physics-Based Numerical Simulations)

, IAU Symposia IAUS 335: Space Weather of the Heliosphere: Processes and Forecasts, Pages: 254-257, ISSN: 1743-9213

Copyright © International Astronomical Union 2018. Advanced forecasting of space weather requires prediction of near-Earth solar-wind conditions on the basis of remote solar observations. This is typically achieved using numerical magnetohydrodynamic models initiated by photospheric magnetic field observations. The accuracy of such forecasts is being continually improved through better numerics, better determination of the boundary conditions and better representation of the underlying physical processes. Thus it is not unreasonable to conclude that simple, empirical solar-wind forecasts have been rendered obsolete. However, empirical models arguably have more to contribute now than ever before. In addition to providing quick, cheap, independent forecasts, simple empirical models aid in numerical model validation and verification, and add value to numerical model forecasts through parameterization, uncertainty estimation and 'downscaling' of sub-grid processes.

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Journal article

Sparks NJ, Hardwick SR, Schmid M, Toumi Ret al., 2017,

IMAGE: a multivariate multi-site stochastic weather generator for European weather and climate

, Stochastic Environmental Research and Risk Assessment, Vol: 32, Pages: 771-784, ISSN: 1436-3240

Capturing the spatial and temporal correlation of multiple variables in a weather generator is challenging. A new massively multi-site, multivariate daily stochastic weather generator called IMAGE is presented here. It models temperature and precipitation variables as latent Gaussian variables with temporal behaviour governed by an auto-regressive model whose residuals and parameters are correlated through resampling of principle component time series of empirical orthogonal function modes. A case study using European climate data demonstrates the model’s ability to reproduce extreme events of temperature and precipitation. The ability to capture the spatial and temporal extent of extremes using a modified Climate Extremes Index is demonstrated. Importantly, the model generates events covering not observed temporal and spatial scales giving new insights for risk management purposes.

Journal article

Masters A, Sulaiman A, Stawarz L, Reville B, Sergis N, Fujimoto M, Burgess D, Coates A, Dougherty Met al., 2017,

An in situ Comparison of Electron Acceleration at Collisionless Shocks under Differing Upstream Magnetic Field Orientations

, Astrophysical Journal, Vol: 843, ISSN: 1538-4357

A leading explanation for the origin of Galactic cosmic rays is acceleration at high-Mach number shock waves in the collisionless plasma surrounding young supernova remnants. Evidence for this is provided by multi-wavelength non-thermal emission thought to be associated with ultrarelativistic electrons at these shocks. However, the dependence of the electron acceleration process on the orientation of the upstream magnetic field with respect to the local normal to the shock front (quasi-parallel/quasi-perpendicular) is debated. Cassini spacecraft observations at Saturn's bow shock have revealed examples of electron acceleration under quasi-perpendicular conditions, and the first in situ evidence of electron acceleration at a quasi-parallel shock. Here we use Cassini data to make the first comparison between energy spectra of locally accelerated electrons under these differing upstream magnetic field regimes. We present data taken during a quasi-perpendicular shock crossing on 2008 March 8 and during a quasi-parallel shock crossing on 2007 February 3, highlighting that both were associated with electron acceleration to at least MeV energies. The magnetic signature of the quasi-perpendicular crossing has a relatively sharp upstream–downstream transition, and energetic electrons were detected close to the transition and immediately downstream. The magnetic transition at the quasi-parallel crossing is less clear, energetic electrons were encountered upstream and downstream, and the electron energy spectrum is harder above ~100 keV. We discuss whether the acceleration is consistent with diffusive shock acceleration theory in each case, and suggest that the quasi-parallel spectral break is due to an energy-dependent interaction between the electrons and short, large-amplitude magnetic structures.

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Cassini Observations of Saturn's High-Mach Number Bow Shock

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