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  • Journal article
    Kurth WS, Hospodarsky GB, Gurnett DA, Lamy L, Dougherty MK, Nichols J, Bunce EJ, Pryor W, Baines K, Stallard T, Melin H, Crary FJet al., 2016,

    Saturn kilometric radiation intensities during the Saturn auroral campaign of 2013

    , Icarus, Vol: 263, Pages: 2-9, ISSN: 1090-2643

    The Saturn auroral campaign carried out in the spring of 2013 used multiple Earth-based observations, remote-sensing observations from Cassini, and in situ-observations from Cassini to further our understanding of auroras at Saturn. Most of the remote sensing and Earth-based measurements are, by nature, not continuous. And, even the in situ measurements, while continuously obtained, are not always obtained in regions relevant to the study of the aurora. Saturn kilometric radiation, however, is remotely monitored nearly continuously by the Radio and Plasma Wave Science instrument on Cassini. This radio emission, produced by the cyclotron maser instability, is tightly tied to auroral processes at Saturn as are auroral radio emissions at other planets, most notably Jupiter and Earth. This paper provides the time history of the intensity of the radio emissions through the auroral campaign as a means of understanding the temporal relationships between the sometimes widely spaced observations of the auroral activity. While beaming characteristics of the radio emissions are known to prevent single spacecraft observations of this emission from being a perfect auroral activity indicator, we demonstrate a good correlation between the radio emission intensity and the level of UV auroral activity, when both measurements are available.
  • Journal article
    Badman SV, Provan G, Bunce EJ, Mitchell DG, Melin H, Cowley SWH, Radioti A, Kurth WS, Pryor WR, Nichols JD, Jinks SL, Stallard TS, Brown RH, Baines KH, Dougherty MKet al., 2016,

    Saturn's auroral morphology and field-aligned currents during a solar wind compression

    , Icarus, Vol: 263, Pages: 83-93, ISSN: 1090-2643

    On 21–22 April 2013, during a coordinated auroral observing campaign, instruments onboard Cassini and the Hubble Space Telescope observed Saturn’s aurora while Cassini traversed Saturn’s high latitude auroral field lines. Signatures of upward and downward field-aligned currents were detected in the nightside magnetosphere in the magnetic field and plasma measurements. The location of the upward current corresponded to the bright ultraviolet auroral arc seen in the auroral images, and the downward current region was located poleward of the upward current in an aurorally dark region. Within the polar cap magnetic field and plasma fluctuations were identified with periods of ∼20 and ∼60 min. The northern and southern auroral ovals were observed to rock in latitude in phase with the respective northern and southern planetary period oscillations. A solar wind compression impacted Saturn’s magnetosphere at the start of 22 April 2013, identified by an intensification and extension to lower frequencies of the Saturn kilometric radiation, with the following sequence of effects: (1) intensification of the auroral field-aligned currents; (2) appearance of a localised, intense bulge in the dawnside (04–06 LT) aurora while the midnight sector aurora remained fainter and narrow; and (3) latitudinal broadening and poleward contraction of the nightside aurora, where the poleward motion in this sector is opposite to that expected from a model of the auroral oval’s usual oscillation. These observations are interpreted as the response to tail reconnection events, initially involving Vasyliunas-type reconnection of closed mass-loaded magnetotail field lines, and then proceeding onto open lobe field lines, causing the contraction of the polar cap region on the night side.
  • Journal article
    Vanniere B, Czaja A, Dacre H, Woollings T, Parfitt Ret al., 2016,

    A Potential Vorticity Signature for the Cold Sector of Winter Extratropical Cyclones

    , Quarterly Journal of the Royal Meteorological Society, Vol: 142, Pages: 432-442, ISSN: 1477-870X

    The cold sector of mid-latitude storms is characterised by distinctive features such as strong surface heat fluxes, shallow convection, convective precipitation and synoptic subsidence. In order to evaluate the contribution of processes occurring in the cold sector to the mean climate, an appropriate indicator is needed. This study describes the systematic presence of negative PV behind the cold front of extratropical storms in winter. The origin of this negative PV is analysed using ERA-Interim data, potential vorticity tendencies averaged over the depth of the boundary layer are evaluated. It is found that negative PV is generated by diabatic processes in the cold sector and by Ekman pumping at the low centre, whereas positive PV is generated by Ekman advection of potential temperature in the warm sector. We suggest here that the negative PV at low-levels can be used to identify the cold sector. A PV-based indicator is applied to estimate the respective contributions of the cold sector and the remainder of the storm to upward motion, and large scale and convective precipitation. We compare the PV-based indicator with other distinctive features that could be used as markers of the cold sector, and find that potential vorticity is the best criterion when taken alone, and the best when combined with any other.
  • Journal article
    Odelstad E, Eriksson AI, Edberg NJT, Johansson F, Vigren E, Andre M, Tzou CY, Carr CM, Cupido Eet al., 2015,

    Evolution of the plasma environment of comet 67P from spacecraft potential measurements by the Rosetta Langmuir probe instrument

    , Geophysical Research Letters, Vol: 42, Pages: 10126-10134, ISSN: 1944-8007

    We study the evolution of the plasma environment of comet 67P using measurements of the spacecraft potential from early September 2014 (heliocentric distance 3.5 AU) to late March 2015 (2.1 AU) obtained by the Langmuir probe (RPC-LAP) instrument. The low collision rate keeps the electron temperature high (~ 5 eV), resulting in a negative spacecraft potential whose magnitude depends on the electron density. This potential is more negative in the northern (summer) hemisphere, particularly over sunlit parts of the neck region on the nucleus, consistent with neutral gas measurements by ROSINA-COPS. Assuming constant electron temperature, the spacecraft potential traces the electron density. This increases as the comet approaches the Sun, most clearly in the southern hemisphere by a factor possibly as high as 20 - 44 between September 2014 and January 2015. The northern hemisphere plasma density increase stays around a factor of around or below 8 - 12, consistent with seasonal insolation change.
  • Journal article
    Arridge CS, Eastwood J, Jackman CM, Poh GK, Slavin JA, Thomsen MF, Andre N, Jia X, Kidder A, Lamy L, Radioti A, Reisenfeld DB, Sergis N, Volwerk M, Walsh AP, Zarka P, Coates AJ, Dougherty MKet al., 2015,

    Cassini in situ observations of long duration magnetic reconnection in Saturn’s magnetotail

    , Nature Physics, Vol: 12, Pages: 268-271, ISSN: 1745-2481

    Magnetic reconnection is a fundamental process in solar system and astrophysical plasmas, through which stored magnetic energy associated with current sheets is converted into thermal, kinetic and wave energy1, 2, 3, 4. Magnetic reconnection is also thought to be a key process involved in shedding internally produced plasma from the giant magnetospheres at Jupiter and Saturn through topological reconfiguration of the magnetic field5, 6. The region where magnetic fields reconnect is known as the diffusion region and in this letter we report on the first encounter of the Cassini spacecraft with a diffusion region in Saturn’s magnetotail. The data also show evidence of magnetic reconnection over a period of 19 h revealing that reconnection can, in fact, act for prolonged intervals in a rapidly rotating magnetosphere. We show that reconnection can be a significant pathway for internal plasma loss at Saturn6. This counters the view of reconnection as a transient method of internal plasma loss at Saturn5, 7. These results, although directly relating to the magnetosphere of Saturn, have applications in the understanding of other rapidly rotating magnetospheres, including that of Jupiter and other astrophysical bodies.
  • Journal article
    Walker SN, Balikhin MA, Shklyar DR, Yearby KH, Canu P, Carr CM, Dandouras Iet al., 2015,

    Experimental determination of the dispersion relation of magnetosonic waves

    , Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 9632-9650, ISSN: 2169-9402

    Magnetosonic waves are commonly observed in the vicinity of the terrestrial magnetic equator. It has been proposed that within this region they may interact with radiation belt electrons, accelerating some to high energies. These wave-particle interactions depend upon the characteristic properties of the wave mode. Hence determination of the wave properties is a fundamental part of understanding these interaction processes. Using data collected during the Cluster Inner Magnetosphere Campaign, this paper identifies an occurrence of magnetosonic waves, discusses their generation and propagation properties from a theoretical perspective, and utilises multispacecraft measurements to experimentally determine their dispersion relation. Their experimental dispersion is found to be in accordance with that based on cold plasma theory.
  • Journal article
    Parfitt R, Czaja A, 2015,

    On the contribution of synoptic transients to the mean atmospheric state in the Gulf Stream region

    , Quarterly Journal of the Royal Meteorological Society, Vol: 142, Pages: 1554-1561, ISSN: 1477-870X

    A new decomposition of the time mean sea level pressure, precipitation, meridional velocity (v) and pressure vertical velocity (ω) is applied to ERA-Interim reanalysis data over the North Atlantic ocean for the December-February 1979–2011 time period. The decomposition suggests that the atmosphere over the Gulf Stream is dominated by a continuous series of synoptic systems, or baroclinic waves, propagating across the region. The time mean value of precipitation, meridional velocity and ω (the latter being taken as a proxy for upward and downward motion) is accordingly set by the propagating waves. The result is particularly striking for ω (v) considering that ascent and descent (poleward and equatorward flow) could reasonably be expected to cancel out in such a series of waves.These results shed a new light on analyses of the storm track heat budget in which the residual between diabatic heating and “transient” eddy heat fluxes (singled out through band pass time filtering or spatial Fourier analysis) is interpreted as a Rossby wave source. This interpretation is questioned because, as a consequence of the filtering used, these studies prevent any direct contribution of the “transients” to the time mean ω or meridional velocity, attributing entirely both fields to the circulation associated with the thermally forced Rossby wave. The fact that “transients” directly contribute to the observed time mean ω over the Gulf Stream might also explain the discrepancy between the observed and predicted response of the vertical motion field to heating in midlatitudes.
  • Journal article
    Hietala H, Drake JF, Phan TD, Eastwood J, McFadden JPet al., 2015,

    Ion temperature anisotropy across a magnetotail reconnection jet

    , Geophysical Research Letters, Vol: 42, Pages: 7239-7247, ISSN: 1944-8007

    A significant fraction of the energy released by magnetotail reconnection appears to go into ion heating, but this heating is generally anisotropic. We examine ARTEMIS dual-spacecraft observations of a long-duration magnetotail exhaust generated by anti-parallel reconnection in conjunction with Particle-In-Cell simulations, showing spatial variations in the anisotropy across the outflow far (> 100di) downstream of the X-line. A consistent pattern is found in both the spacecraft data and the simulations: Whilst the total temperature across the exhaust is rather constant, near the boundaries Ti,|| dominates. The plasma is well-above the firehose threshold within patchy spatial regions at |BX| ∈ [0.1, 0.5]B0, suggesting that the drive for the instability is strong and the instability is too weak to relax the anisotropy. At the mid-plane (|BX|0.1 B0), Ti,⊥ > Ti,|| and ions undergo Speiser-like motion despite the large distance from the X-line.
  • Journal article
    Pilkington NM, Achilleos N, Arridge CS, Guio P, Masters A, Ray LC, Sergis N, Thomsen MF, Coates AJ, Dougherty MKet al., 2015,

    Asymmetries observed in Saturn's magnetopause geometry

    , Geophysical Research Letters, Vol: 42, Pages: 6890-6898, ISSN: 1944-8007

    For over 10 years, the Cassini spacecraft has patrolled Saturn's magnetosphere and observed its magnetopause boundary over a wide range of prevailing solar wind and interior plasma conditions. We now have data that enable us to resolve a significant dawn-dusk asymmetry and find that the magnetosphere extends farther from the planet on the dawnside of the planet by 7 ± 1%. In addition, an opposing dawn-dusk asymmetry in the suprathermal plasma pressure adjacent to the magnetopause has been observed. This probably acts to reduce the size asymmetry and may explain the discrepancy between the degree of asymmetry found here and a similar asymmetry found by Kivelson and Jia (2014) using MHD simulations. Finally, these observations sample a wide range of season, allowing the “intrinsic” polar flattening (14 ± 1%) caused by the magnetodisc to be separated from the seasonally induced north-south asymmetry in the magnetopause shape found theoretically (5 ± 1% when the planet's magnetic dipole is tilted away from the Sun by 10–17°).
  • Journal article
    Osipov S, Stenchikov G, Brindley H, Banks Jet al., 2015,

    Diurnal cycle of the dust instantaneous direct radiative forcing over the Arabian Peninsula

    , Atmospheric Chemistry and Physics, Vol: 15, Pages: 9537-9553, ISSN: 1680-7324

    In this study we attempted to better quantify radiative effects of dust over the Arabian Peninsula and their dependence on input parameters. For this purpose we have developed a stand-alone column radiation transport model coupled with the Mie, T-matrix and geometric optics calculations and driven by reanalysis meteorological fields and atmospheric composition. Numerical experiments were carried out for a wide range of aerosol optical depths, including extreme values developed during the dust storm on 18–20 March 2012. Comprehensive ground-based observations and satellite retrievals were used to estimate aerosol optical properties, validate calculations and carry out radiation closure. The broadband surface albedo, fluxes at the bottom and top of the atmosphere as well as instantaneous dust radiative forcing were estimated both from the model and observations. Diurnal cycle of the shortwave instantaneous dust direct radiative forcing was studied for a range of aerosol and surface characteristics representative of the Arabian Peninsula. Mechanisms and parameters responsible for diurnal variability of the radiative forcing were evaluated. We found that intrinsic variability of the surface albedo and its dependence on atmospheric conditions, along with anisotropic aerosol scattering, are mostly responsible for diurnal effects.
  • Journal article
    Richter I, Koenders C, Auster H-U, Fruhauff D, Gotz C, Heinisch P, Perschke C, Motschmann U, Stoll B, Altwegg K, Burch J, Carr CM, Cupido E, Eriksson A, Henri P, Goldstein R, Lebreton J-P, Mokashi P, Nemeth Z, Nilsson H, Rubin M, Szego K, Tsurutani BT, Vallat C, Volwerk C, Volwerk M, Glassmeier K-Het al., 2015,

    Observation of a new type of low frequency waves at comet 67P/Churyumov-Gerasimenko

    , Annales Geophysicae, Vol: 33, Pages: 1031-1036, ISSN: 1432-0576

    We report on magnetic field measurements madein the innermost coma of 67P/Churyumov-Gerasimenkoin its low activity state. Quasi-coherent, large-amplitude(δB/B ∼ 1), compressional magnetic field oscillations at5 ∼ 40 mHz dominate the immediate plasma environmentof the nucleus. This differs from previously studied cometinteractionregions where waves at the cometary ion gyrofrequenciesare the main feature. Thus classical pick-up iondriven instabilities are unable to explain the observations. We10 propose a cross-field current instability associated with newborncometary ion currents as a possible source mechanism
  • Journal article
    Auster H-U, Apathy I, Berghofer G, Fornacon K-H, Remizov A, Carr C, Guttler C, Haerendel G, Heinisch P, Hercik D, Hilchenbach M, Kuhrt E, Magnes W, Motschmann U, Richter I, Russell CT, Przyklenk A, Schwingenschuh K, Sierks H, Glassmeier K-Het al., 2015,

    The nonmagnetic nucleus of comet 67P/Churyumov-Gerasimenko

    , Science, Vol: 349, Pages: aaa5102-aaa5102, ISSN: 0036-8075
  • Journal article
    Ryder CL, McQuaid JB, Flamant C, Rosenberg PD, Washington R, Brindley HE, Highwood EJ, Marsham JH, Parker DJ, Todd MC, Banks JR, Brooke JK, Engelstaedter S, Estelles V, Formenti P, Garcia-Carreras L, Kocha C, Marenco F, Sodemann H, Allen CJT, Bourdon A, Bart M, Cavazos-Guerra C, Chevaillier S, Crosier J, Darbyshire E, Dean AR, Dorsey JR, Kent J, O'Sullivan D, Schepanski K, Szpek K, Trembath J, Woolley Aet al., 2015,

    Advances in understanding mineral dust and boundary layer processes over the Sahara from Fennec aircraft observations

    , Atmospheric Chemistry and Physics, Vol: 15, Pages: 8479-8520, ISSN: 1680-7324
  • Journal article
    Voulgarakis A, Marlier ME, Faluvegi G, Shindell DT, Tsigaridis K, Mangeon Set al., 2015,

    Interannual variability of tropospheric trace gases and aerosols: The role of biomass burning emissions

    , Journal of Geophysical Research: Atmospheres, Vol: 120, Pages: 7157-7173, ISSN: 2169-897X

    Fires are responsible for a range of gaseous and aerosol emissions. However, their influence onthe interannual variability of atmospheric trace gases and aerosols has not been systematically investigatedfrom a global perspective. We examine biomass burning emissions as a driver of interannual variability oflarge-scale abundances of short-lived constituents such as carbon monoxide (CO), hydroxyl radicals (OH),ozone, and aerosols using the Goddard Institute for Space Studies ModelE composition-climate model and arange of observations, with an emphasis on satellite information. Our model captures the observed variabilityof the constituents examined in most cases, but with substantial underestimates in boreal regions. Thestrongest interannual variability on a global scale is found for carbon monoxide (~10% for its global annualburden), while the lowest is found for tropospheric ozone (~1% for its global annual burden). Regionally,aerosol optical depth shows the largest variability which exceeds 50%. Areas of strong variability of bothaerosols and CO include the tropical land regions (especially Equatorial Asia and South America) and northernhigh latitudes, while even regions in the northern midlatitudes experience substantial interannual variability ofaerosols. Ozone variability peaks over equatorial Asia in boreal autumn, partly due to varying biomass burningemissions, and over the western and central Pacific in the rest of the year, mainly due to meteorologicalfluctuations. We find that biomass burning emissions are almost entirely responsible for global CO interannualvariability, and similarly important for OH variability. The same is true for global and regional aerosol variability,especially when not taking into account dust and sea-salt particles. We show that important implications canarise from such interannual influences for regional climate and air quality
  • Journal article
    Balikhin MA, Shprits YY, Walker SN, Chen L, Cornilleau-Wehrlin N, Dandouras I, Santolik O, Carr C, Yearby KH, Weiss Bet al., 2015,

    Observations of discrete harmonics emerging from equatorial noise.

    , Nature Communications, Vol: 6, ISSN: 2041-1723

    A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as 'equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes 'ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations.
  • Journal article
    Horbury TS, Archer MO, Brown P, Eastwood JP, Oddy TM, Whiteside BJ, Sample JGet 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: 1432-0576

    We 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.
  • Journal article
    Nilsson H, Wieser GS, Behar E, Wedlund CS, Kallio E, Gunell H, Edberg NJT, Eriksson AI, Yamauchi M, Koenders C, Wieser M, Lundin R, Barabash S, Mandt K, Burch JL, Goldstein R, Mokashi P, Carr CM, Cupido E, Fox PT, Szego K, Nemeth Z, Fedorov A, Sauvaud JA, Koskinen H, Richter I, Lebreton JP, Henri P, Volwerk M, Vallat C, Geiger Bet 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: 0004-6361

    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.
  • Journal article
    Carr CM, Edberg NJT, Eriksson AI, Odelstad E, Henri P, Lebreton J-P, Gasc S, Rubin M, Andre M, Gill R, Johansson EPG, Johansson F, Vigren E, Wahlund JE, Cupido E, Glassmeier K-H, Goldstein R, Koenders C, Mandt K, Nemeth Z, Nilsson H, Richter I, Stenberg Wieser G, Szego K, Volwerk Met 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: 1944-8007

    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.
  • Journal article
    Mangeon T, Field R, Fromm M, McHugh C, Voulgarakis Aet 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: 2053-0196

    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.
  • Journal article
    Voulgarakis A, Field RD, 2015,

    Fire influences on atmospheric composition, air quality, and climate

    , 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.
  • Journal article
    Dunlop MW, Yang J-Y, Yang Y-Y, Xiong C, Lühr H, Bogdanova YV, Shen C, Olsen N, Zhang Q-H, Cao J-B, Fu H-S, Liu W-L, Carr CM, Ritter P, Masson A, Haagmans Ret al., 2015,

    Simultaneous field-aligned currents at Swarm and Cluster satellites

    , 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.
  • Journal article
    Carr CM, Erikksson S, Lapenta G, Newman DL, Phan TD, Gosling JT, Lavraud B, Khotyaintsev YV, Markidis S, Goldman MVet al., 2015,

    On Multiple Reconnection X-lines and Tripolar Perturbations of Strong Guide Magnetic Fields

    , 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.
  • Journal article
    Czaja 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
  • Journal article
    Eastwood JP, Hietala H, Toth G, Phan TD, Fujimoto Met al., 2015,

    What Controls the Structure and Dynamics of Earth's Magnetosphere?

    , SPACE SCIENCE REVIEWS, Vol: 188, Pages: 251-286, ISSN: 0038-6308
  • Journal article
    Hu F, Sun J, Brindley HE, Liang X, Lucyszyn Set al., 2015,

    Systems Analysis for Thermal Infrared 'THz Torch' Applications

    , JOURNAL OF INFRARED MILLIMETER AND TERAHERTZ WAVES, Vol: 36, Pages: 474-495, ISSN: 1866-6892
  • Journal article
    Balogh A, Bykov A, Eastwood J, Kaastra Jet al., 2015,

    Multi-scale Structure Formation and Dynamics in Cosmic Plasmas

    , SPACE SCIENCE REVIEWS, Vol: 188, Pages: 1-2, ISSN: 0038-6308
  • 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
  • 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
  • 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.
  • 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

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