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  • JOURNAL ARTICLE
    Arridge CS, Eastwood JP, Jackman CM, Poh G-K, 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 MK, Arridge CS, Eastwood JP, Jackman CM, Poh GK, Slavin JA, Thomsen MF, André N, Jia X, Kidder A, Lamy L, Radioti A, Reisenfeld DB, Sergis N, Volwerk M, Walsh AP, Zarka P, Coates AJ, Dougherty MK, Arridge CS, Eastwood JP, Jackman CM, Poh G-K, Slavin JA, Thomsen MF, André N, Jia X, Kidder A, Lamy L, Radioti A, Reisenfeld DB, Sergis N, Volwerk M, Walsh AP, Zarka P, Coates AJ, Dougherty MK, 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., 2016,

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

    , NATURE PHYSICS, Vol: 12, Pages: 268-271, ISSN: 1745-2473

    © 2016 Macmillan Publishers Limited. 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 energy. 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 field. 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 Saturn. This counters the view of reconnection as a transient method of internal plasma loss at Saturn. 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
    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 MK, 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 MK, 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: 0019-1035

    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
    Kurth WS, Hospodarsky GB, Gurnett DA, Lamy L, Dougherty MK, Nichols J, Bunce EJ, Pryor W, Baines K, Stallard T, Melin H, Crary FJ, Kurth WS, Hospodarsky GB, Gurnett DA, Lamy L, Dougherty MK, Nichols J, Bunce EJ, Pryor W, Baines K, Stallard T, Melin H, Crary FJ, 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: 0019-1035

    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
    Mangeon S, Field R, Fromm M, McHugh C, Voulgarakis A, Mangeon T, Field R, Fromm M, McHugh C, Voulgarakis Aet al., 2016,

    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
    Parfitt R, Czaja A, Parfitt R, Czaja A, Parfitt R, Czaja A, Parfitt R, Czaja Aet al., 2016,

    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: 0035-9009

    © 2016 Royal Meteorological Society. 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
    Phan TD, Shay MA, Eastwood JP, Angelopoulos V, Oieroset M, Oka M, Fujimoto M, Phan TD, Shay MA, Eastwood JP, Angelopoulos V, Oieroset M, Oka M, Fujimoto Met al., 2016,

    Establishing the Context for Reconnection Diffusion Region Encounters and Strategies for the Capture and Transmission of Diffusion Region Burst Data by MMS

    , Space Science Reviews, Vol: 199, Pages: 631-650, ISSN: 0038-6308

    © 2015, The Author(s). This paper describes the efforts of our Inter-Disciplinary Scientist (IDS) team to (a) establish the large-scale context for reconnection diffusion region encounters by MMS at the magnetopause and in the magnetotail, including the distinction between X-line and O-line encounters, that would help the identification of diffusion regions in spacecraft data, and (b) devise possible strategies that can be used by MMS to capture and transmit burst data associated with diffusion region candidates. At the magnetopause we suggest the strategy of transmitting burst data from all magnetopause crossings so that no magnetopause reconnection diffusion regions encountered by the spacecraft will be missed. The strategy is made possible by the MMS mass memory and downlink budget. In the magnetotail, it is estimated that MMS will be able to transmit burst data for all diffusion regions, all reconnection jet fronts (a.k.a. dipolarization fronts) and separatrix encounters, but less than 50 % of reconnection exhausts encountered by the spacecraft. We also discuss automated burst trigger schemes that could capture various reconnection-related phenomena. The identification of candidate diffusion region encounters by the burst trigger schemes will be verified and improved by a Scientist-In-The-Loop (SITL). With the knowledge of the properties of the region surrounding the diffusion region and the combination of automated burst triggers and further optimization by the SITL, MMS should be able to capture most diffusion regions it encounters.
  • JOURNAL ARTICLE
    Vanniere B, Czaja A, Dacre H, Woollings T, Parfitt R, Vannière B, Czaja A, Dacre H, Woollings T, Parfitt R, Vannière B, Czaja A, Dacre H, Woollings T, Parfitt R, 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: 0035-9009

    © 2016 Royal Meteorological Society. The cold sector of a midlatitude storm is characterized 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 potential vorticity (PV) behind the cold front of extratropical storms in winter. The origin of this negative PV is analyzed using ERA-Interim data, and PV 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 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
    Archer MO, Horbury TS, Brown P, Eastwood JP, Oddy TM, Whiteside BJ, Sample JG, Archer MO, Horbury TS, Brown P, Eastwood JP, Oddy TM, Whiteside BJ, Sample JG, Archer MO, Horbury TS, Brown P, Eastwood JP, Oddy TM, Whiteside BJ, Sample JG, 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: 0992-7689

    © Author(s) 2015. 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
    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-H, Auster H-U, Apathy I, Berghofer G, Fornacon K-H, Remizov A, Carr C, Guettler C, Haerendel G, Heinisch P, Hercik D, Hilchenbach M, Kuehrt E, Magnes W, Motschmann U, Richter I, Russell CT, Przyklenk A, Schwingenschuh K, Sierks H, Glassmeier K-H, Auster H-U, Apathy I, Berghofer G, Fornacon K-H, Remizov A, Carr C, Güttler C, Haerendel G, Heinisch P, Hercik D, Hilchenbach M, Kührt E, Magnes W, Motschmann U, Richter I, Russell CT, Przyklenk A, Schwingenschuh K, Sierks H, Glassmeier K-H, Auster HU, Apathy I, Berghofer G, Fornacon KH, Remizov A, Carr C, Güttler C, Haerendel G, Heinisch P, Hercik D, Hilchenbach M, Kührt E, Magnes W, Motschmann U, Richter I, Russell CT, Przyklenk A, Schwingenschuh K, Sierks H, Glassmeier KH, Auster HU, Apathy I, Berghofer G, Fornacon KH, Remizov A, Carr C, Güttler C, Haerendel G, Heinisch P, Hercik D, Hilchenbach M, Kührt E, Magnes W, Motschmann U, Richter I, Russell CT, Przyklenk A, Schwingenschuh K, Sierks H, Glassmeier KH, Carr CM, Auster H-U, Apathy I, Berghofer G, Fornacon K-H, Remizov A, Guettler C, Haerendal G, Heinisch P, Hercik D, Hilchenbach M, Kuehrt E, Magnes W, Motschmann U, Richter I, Russell C, 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

    Knowledge of the magnetization of planetary bodies constrains their origin and evolution, as well as the conditions in the solar nebular at that time. On the basis of magnetic field measurements during the descent and subsequent multiple touchdown of the Rosetta lander Philae on the comet 67P/Churyumov-Gerasimenko (67P), we show that no global magnetic field was detected within the limitations of analysis. The Rosetta Magnetometer and Plasma Monitor (ROMAP) suite of sensors measured an upper magnetic field magnitude of less than 2 nanotesla at the cometary surface at multiple locations, with the upper specific magnetic moment being <3.1 × 10(-5) ampere-square meters per kilogram for meter-size homogeneous magnetized boulders. The maximum dipole moment of 67P is 1.6 × 10(8) ampere-square meters. We conclude that on the meter scale, magnetic alignment in the preplanetary nebula is of minor importance.
  • JOURNAL ARTICLE
    Balikhin MA, Shprits YY, Walker SN, Chen L, Cornilleau-Wehrlin N, Dandouras I, Santolik O, Carr C, Yearby KH, Weiss B, Balikhin MA, Shprits YY, Walker SN, Chen L, Cornilleau-Wehrlin N, Dandouras I, Santolik O, Carr C, Yearby KH, Weiss B, Balikhin MA, Shprits YY, Walker SN, Chen L, Cornilleau-Wehrlin N, Dandouras I, Santolik O, Carr C, Yearby KH, Weiss B, Balikhin MA, Shprits YY, Walker SN, Chen L, Cornilleau-Wehrlin N, Dandouras I, Santolik O, Carr C, Yearby KH, Weiss B, Balikhin MA, Shprits YY, Walker SN, Chen L, Cornilleau-Wehrlin N, Dandouras I, Santolik O, Carr C, Yearby KH, Weiss B, 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, Pages: 7703-7703, 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
    Balogh A, Bykov A, Eastwood J, Kaastra J, Balogh A, Bykov A, Eastwood J, Kaastra J, Balogh A, Bykov AM, Eastwood JP, Kaastra JS, 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

    The Space Science Review Journal is composed from the reviews from a workshop titled 'Multi-scale structure formation and dynamics in cosmic plasmas' which was held at International Space Science Institute in April 2013. It contains review papers on the basic processes of structure formation in cosmic plasmas starting from electric currents, which produce magnetic structures in planet magnetospheres, stellar winds, and relativistic plasma outflows like pulsar wind nebulae and Active Galactic Nuclei jets. The important role of the helicity concept on the structure formation and evolution of the large scale magnetic fields in highly conductive cosmic plasmas is emphasized in the book. Cosmological aspects of plasma structures are reviewed within a discussion of large-scale structure formation from the first non-linear objects to massive galaxy clusters, which is followed by a review of observations and current models of structures and components in galaxy clusters. The properties of magnetic field fluctuations and structures in the outer solar atmosphere and Earth?s magneto-tail, which have direct implications for the general problem of structure formation in hot plasmas, are discussed in depth.
  • JOURNAL ARTICLE
    Beth A, Garnier P, Toublanc D, Dandouras I, Mazelle C, Beth A, Garnier P, Toublanc D, Dandouras I, Mazelle C, Beth A, Garnier P, Toublanc D, Dandouras I, Mazelle Cet al., 2015,

    Theory for planetary exospheres: II. Radiation pressure effect on exospheric density profiles

    , Icarus, Vol: 266, Pages: 423-432, ISSN: 0019-1035

    © 2015 The Authors. The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this second part of our work, we present here the density profiles of atomic Hydrogen in planetary exospheres subject to the radiation pressure. We first provide the altitude profiles of ballistic particles (the dominant exospheric population in most cases), which exhibit strong asymmetries that explain the known geotail phenomenon at Earth. The radiation pressure strongly enhances the densities compared with the pure gravity case (i.e. the Chamberlain profiles), in particular at noon and midnight. We finally show the existence of an exopause that appears naturally as the external limit for bounded particles, above which all particles are escaping.
  • JOURNAL ARTICLE
    Beth A, Garnier P, Toublanc D, Dandouras I, Mazelle C, Beth A, Garnier P, Toublanc D, Dandouras I, Mazelle C, Beth A, Garnier P, Toublanc D, Dandouras I, Mazelle Cet al., 2015,

    Theory for planetary exospheres: I. Radiation pressure effect on dynamical trajectories

    , Icarus, Vol: 266, Pages: 410-422, ISSN: 0019-1035

    © 2015 The Authors. The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalisation of the study by Bishop and Chamberlain (Bishop, J., Chamberlian, J.W. [1989]. Icarus 81, 145-163). In this first paper, we present the complete solutions of particles trajectories, which are not conics, under the influence of the solar radiation pressure with some assumptions. This problem is similar to the classical Stark problem (Stark, J. [1914] . Ann. Phys. 348, 965-982). This problem was largely tackled in the literature and more specifically, recently by Lantoine and Russell (Lantoine, G., Russell, R.P. [2011]. Celest. Mech. Dynam. Astron. 109, 333-366) and by Biscani and Izzo (Biscani, F., Izzo, D. [2014] . Mon. Not. R. Astron. Soc. 439, 810-822) as we will discuss in this paper. We give here the full set of solutions for the motion of a particle (in our case for an atom or a molecule), i.e. the space coordinates and the time solution for bounded and unbounded trajectories in terms of Jacobi elliptic functions. We thus provide here the complete set of solutions for this so-call Stark effect (Stark, J. [1914]. Ann. Phys. 348, 965-982) in terms of Jacobi elliptic functions (Jacobi, C.G.J. [1829] . Fundamenta nova theoriae functionum ellipticarum. Sumtibus fratrum), which may be used to model the trajectories of particles in planetary exospheres.
  • JOURNAL ARTICLE
    Brindley H, Bantges R, Russell J, Murray J, Dancel C, Belotti C, Harries J, 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
    Czaja A, Marshall J, Czaja A, Marshall J, Czaja A, Marshall Jet al., 2015,

    Why is there net surface heating over the Antarctic Circumpolar Current?

    , OCEAN DYNAMICS, Vol: 65, Pages: 751-760, ISSN: 1616-7341

    © 2015, Springer-Verlag Berlin Heidelberg. Using a combination of atmospheric reanalysis data, climate model outputs and a simple model, key mechanisms controlling net surface heating over the Southern Ocean are identified. All data sources used suggest that, in a streamline-averaged view, net surface heating over the Antarctic Circumpolar Current (ACC) is a result of net accumulation of solar radiation rather than a result of heat gain through turbulent fluxes (the latter systematically cool the upper ocean). It is proposed that the fraction of this net radiative heat gain realized as net ACC heating is set by two factors. First, the sea surface temperature at the southern edge of the ACC. Second, the relative strength of the negative heatflux feedbacks associated with evaporation at the sea surface and advection of heat by the residual flow in the oceanic mixed layer. A large advective feedback and a weak evaporative feedback maximize net ACC heating. It is shown that the present Southern Ocean and its circumpolar current are in this heating regime.
  • 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 R, Dunlop MW, Yang J-Y, Yang Y-Y, Xiong C, Luehr 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 R, Dunlop MW, Yang JY, Yang YY, Xiong C, Lühr H, Bogdanova YV, Shen C, Olsen N, Zhang QH, Cao JB, Fu HS, Liu WL, Carr CM, Ritter P, Masson A, Haagmans R, 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
    Eastwood JP, Goldman MV, Hietala H, Newman DL, Mistry R, Lapenta G, Eastwood JP, Goldman MV, Hietala H, Newman DL, Mistry R, Lapenta G, Eastwood JP, Goldman MV, Hietala H, Newman DL, Mistry R, Lapenta G, Eastwood JP, Goldman MV, Hietala H, Newman DL, Mistry R, Lapenta G, 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: 2169-9380

    ©2014. The Authors. 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
    Eastwood JP, Hietala H, Toth G, Phan TD, Fujimoto M, Eastwood JP, Hietala H, Toth G, Phan TD, Fujimoto M, Eastwood JP, Hietala H, Tóth G, Phan T, Fujimoto M, 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

    © 2014, The Author(s). Unlike most cosmic plasma structures, planetary magnetospheres can be extensively studied in situ. In particular, studies of the Earth’s magnetosphere over the past few decades have resulted in a relatively good experimental understanding of both its basic structural properties and its response to changes in the impinging solar wind. In this article we provide a broad overview, designed for researchers unfamiliar with magnetospheric physics, of the main processes and parameters that control the structure and dynamics of planetary magnetospheres, especially the Earth’s. In particular, we concentrate on the structure and dynamics of three important regions: the bow shock, the magnetopause and the magnetotail. In the final part of this review we describe the current status of global magnetospheric modelling, which is crucial to placing in situ observations in the proper context and providing a better understanding of magnetospheric structure and dynamics under all possible input conditions. Although the parameter regime experienced in the solar system is limited, the plasma physics that is learned by studying planetary magnetospheres can, in principle, be translated to more general studies of cosmic plasma structures. Conversely, studies of cosmic plasma under a wide range of conditions should be used to understand Earth’s magnetosphere under extreme conditions. We conclude the review by discussing this and summarizing some general properties and principles that may be applied to studies of other cosmic plasma structures.
  • JOURNAL ARTICLE
    Eastwood JP, Kataria DO, McInnes CR, Barnes NC, Mulligan P, Eastwood JP, Kataria DO, McInnes CR, Barnes NC, Mulligan P, Eastwood JP, Kataria DO, McInnes CR, Barnes NC, Mulligan Pet al., 2015,

    Sunjammer

    , WEATHER, Vol: 70, Pages: 27-30, ISSN: 0043-1656
  • JOURNAL ARTICLE
    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, Carr CM, Cupido E, Glassmeier K-H, Goldstein R, Koenders C, Mandt K, Nemeth Z, Nilsson H, Richter I, Wieser GS, Szego K, Volwerk M, Edberg NJT, Eriksson AI, Odelstad E, Henri P, Lebreton JP, Gasc S, Rubin M, André M, Gill R, Johansson EPG, Johansson F, Vigren E, Wahlund JE, Carr CM, Cupido E, Glassmeier KH, Goldstein R, Koenders C, Mandt K, Nemeth Z, Nilsson H, Richter I, Wieser GS, Szego K, Volwerk M, Edberg NJT, Eriksson AI, Odelstad E, Henri P, Lebreton J-P, Gasc S, Rubin M, André M, Gill R, Johansson EPG, Johansson F, Vigren E, Wahlund JE, Carr CM, Cupido E, Glassmeier K-H, Goldstein R, Koenders C, Mandt K, Nemeth Z, Nilsson H, Richter I, Wieser GS, Szego K, Volwerk M, Edberg NJT, Eriksson AI, Odelstad E, Henri P, Lebreton J-P, Gasc S, Rubin M, André M, Gill R, Johansson EPG, Johansson F, Vigren E, Wahlund JE, Carr CM, Cupido E, Glassmeier K-H, Goldstein R, Koenders C, Mandt K, Nemeth Z, Nilsson H, Richter I, Wieser GS, Szego K, Volwerk M, 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 comet 67P/CG from Rosetta measurements

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 4263-4269, ISSN: 0094-8276

    ©2015. American Geophysical Union. All Rights Reserved. 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 < sup > -6 < /sup > , 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
    Eriksson S, Lapenta G, Newman DL, Phan TD, Gosling JT, Lavraud B, Khotyaintsev YV, Carr CM, Markidis S, Goldman MV, Eriksson S, Lapenta G, Newman DL, Phan TD, Gosling JT, Lavraud B, Khotyaintsev YV, Carr CM, Markidis S, Goldman MV, Eriksson S, Lapenta G, Newman DL, Phan TD, Gosling JT, Lavraud B, Khotyaintsev YV, Carr CM, Markidis S, Goldman MV, 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

    , ASTROPHYSICAL JOURNAL, Vol: 805, Pages: 43-43, ISSN: 0004-637X

    © 2015. The American Astronomical Society. All rights reserved. We report new multi-spacecraft Cluster observations of tripolar guide magnetic field perturbations at a solar wind reconnection exhaust in the presence of a guide field B M which is almost four times as strong as the reversing field B L . The novel tripolar field consists of two narrow regions of depressed B M , with an observed 7%-14% ΔB M magnitude relative to the external field, which are found adjacent to a wide region of enhanced B M within the exhaust. A stronger reversing field is associated with each B M depression. A kinetic reconnection simulation for realistic solar wind conditions and the observed strong guide field reveals that tripolar magnetic fields preferentially form across current sheets in the presence of multiple X-lines as magnetic islands approach one another and merge into fewer and larger islands. The simulated ΔB M /ΔX N over the normal width ΔX N between a B M minimum and the edge of the external region agree with the normalized values observed by Cluster. We propose that a tripolar guide field perturbation may be used to identify candidate regions containing multiple X-lines and interacting magnetic islands at individual solar wind current sheets with a strong guide field.
  • JOURNAL ARTICLE
    Hietala H, Drake JF, Phan TD, Eastwood JP, McFadden JP, Hietala H, Drake JF, Phan TD, Eastwood JP, McFadden JP, Hietala H, Drake JF, Phan TD, Eastwood JP, McFadden JP, Hietala H, Drake JF, Phan TD, Eastwood JP, Mcfadden JP, Hietala H, Drake JF, Phan TD, Eastwood JP, McFadden JP, Hietala H, Drake JF, Phan TD, Eastwood JP, McFadden JP, 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: 0094-8276

    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 antiparallel 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: While 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 midplane ( |BX|≲0.1B0), Ti,⊥>Ti,|| and ions undergo Speiser-like motion despite the large distance from the X line.
  • JOURNAL ARTICLE
    Hu F, Sun J, Brindley HE, Liang X, Lucyszyn S, Hu F, Sun J, Brindley HE, Liang X, Lucyszyn S, 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

    The ‘THz Torch’ concept was recently introduced by the authors for providing secure wireless communications over short distances within the thermal infrared (10-100 THz). Unlike conventional systems, thermal infrared can exploit front-end thermodynamics with engineered blackbody radiation. For the first time, a detailed power link budget analysis is given for this new form of wireless link. The mathematical modeling of a short end-to-end link is provided, which integrates thermodynamics into conventional signal and noise power analysis. As expected from the Friis formula for noise, it is found that the noise contribution from the pyroelectric detector dominates intrinsic noise. From output signal and noise voltage measurements, experimental values for signal-to-noise ratio (SNR) are obtained and compared with calculated predictions. As with conventional communications systems, it is shown for the first time that the measured SNR and measured bit error rate found with this thermodynamics-based system resembles classical empirical models. Our system analysis can serve as an invaluable tool for the development of thermal infrared systems, accurately characterizing each individual channel and, thus, enables the performance of multi-channel ‘THz Torch’ systems to be optimized.
  • JOURNAL ARTICLE
    Klueser L, Banks JR, Martynenko D, Bergemann C, Brindley HE, Holzer-Popp T, Klüser L, Banks JR, Martynenko D, Bergemann C, Brindley HE, Holzer-Popp Tet al., 2015,

    Information content of space-borne hyperspectral infrared observations with respect to mineral dust properties

    , REMOTE SENSING OF ENVIRONMENT, Vol: 156, Pages: 294-309, ISSN: 0034-4257
  • JOURNAL ARTICLE
    Leitner S, Valavanoglou A, Brown P, Hagen C, Magnes W, Whiteside BJ, Carr CM, Delva M, Baumjohann W, Leitner S, Valavanoglou A, Brown P, Hagen C, Magnes W, Whiteside BJ, Carr CM, Delva M, Baumjohann W, Leitner S, Valavanoglou A, Brown P, Hagen C, Magnes W, Whiteside BJ, Carr CM, Delva M, Baumjohann Wet al., 2015,

    Design of the Magnetoresistive Magnetometer for ESA's SOSMAG Project

    , IEEE TRANSACTIONS ON MAGNETICS, Vol: 51, Pages: 1-4, ISSN: 0018-9464

    © 1965-2012 IEEE. A prototype of a Service Oriented Spacecraft Magnetometer (SOSMAG) is being developed for European Space Agency's Space Situational Awareness program, which shall serve as a ready-to-use space weather monitoring system to be mounted on a variety of different spacecraft built without a magnetic cleanliness program. The separation between the natural magnetic field in space and the artificial magnetic field generated by the spacecraft is one of the key issues for its successful performance. The SOSMAG design is based on two types of magnetic sensors. One or two low-noise fluxgate sensors for the required high measurement accuracy will be mounted along a boom of length 1 m, and two anisotropic magnetoresistance (AMR)-based sensors will be used within the spacecraft for detection and characterization of its magnetic disturbances. This paper presents the design and performance of the AMR magnetometer that contains an application-specified integrated circuit (ASIC) and a hybrid sensor as core elements. The magnetometer front-end ASIC, originally developed for National Aeronautics and Space Administration's Magnetospheric Multiscale mission, is based on a fourth-order sigma-delta A/D converter design. All the active electronics needed for the readout of the AMR sensor and its digitization, as well as for digitizing the magnetometer's housekeeping data are part of the ASIC. Each of the three-axis hybrid sensors consists of a ceramics circuit board with three HMC1021 sensor elements, one bypass capacitor, a temperature sensor, and a MOSFET driver mounted in chip-on-board technology. A novel approach is used to set and reset the AMR elements. It is done in a narrow-pulsed way at 32 kHz with a pulsewidth of only 238 ns, thus minimizing the required excitation power to 30 mW in total.
  • JOURNAL ARTICLE
    Mistry R, Eastwood JP, Hietala H, Mistry R, Eastwood JP, Hietala H, Mistry R, Eastwood JP, Hietala H, Mistry R, Eastwood JP, Hietala H, Mistry R, Eastwood JP, Hietala Het al., 2015,

    Detection of small-scale folds at a solar wind reconnection exhaust

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 120, Pages: 30-42, ISSN: 2169-9380

    ©2014. American Geophysical Union. All Rights Reserved. Observations of reconnection in the solar wind over the last few years appear to indicate that the majority of large-scale reconnecting current sheets are roughly planar, and that reconnection itself is quasi-steady. Most studies of solar wind exhausts have used spacecraft with large separations and relatively low time cadence ion measurements. Here we present multipoint Cluster observations of a reconnection exhaust and the associated current sheet at ACE and Wind, enabling it to be studied on multiple length scales and at high time resolution. While analysis shows that on large scales the current sheet is planar, detailed measurements using the four closely spaced Cluster spacecraft show that the trailing edge of the reconnection jet is nonplanar with folds orthogonal to the reconnection plane, with length scales of approximately 230 ion inertial lengths. Our findings thus suggest that while solar wind current sheets undergoing reconnection may be planar on large scales, they may also exhibit complex smaller-scale structure. Such structure is difficult to observe and has rarely been detected because exhausts are rapidly convected past the spacecraft in a single cut; there is therefore a limited set of spacecraft trajectories through the exhaust which would allow the nonplanar features to be intercepted. We consider how such nonplanar reconnection current sheets can form and the processes which may have generated the 3-D structure that was observed.
  • 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 J, 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, ISSN: 1942-2466
  • 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 M, Nilsson H, Stenberg Wieser G, 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 M, 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 JA, Koskinen H, Kallio E, Lebreton JP, Eriksson A, Edberg N, Goldstein R, Henri P, Koenders C, Mokashi P, Nemeth Z, Richter I, Szego K, Volwerk M, Vallat C, Rubin M, Nilsson H, Stenberg Wieser G, Behar E, Wedlund CS, Gunell H, Yamauchi M, Lundin R, Barabash S, Wieser M, Carr C, Cupido E, Burch JL, Fedorov A, Sauvaud JA, Koskinen H, Kallio E, Lebreton JP, Eriksson A, Edberg N, Goldstein R, Henri P, Koenders C, Mokashi P, Nemeth Z, Richter I, Szego K, Volwerk M, Vallat C, Rubin M, Nilsson H, Stenberg Wieser G, 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, Pages: aaa0571-aaa0571, 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.
  • 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 C, Cupido E, Fox PT, Szego K, Nemeth Z, Fedorovn A, Sauvaud J-A, Koskinen H, Richter I, Lebreton J-P, Henri P, Volwerk M, Vallat C, Geiger B, Nilsson H, Stenberg Wieser G, Behar E, Simon Wedlund C, 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 C, 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 B, Nilsson H, Stenberg Wieser G, Behar E, Simon Wedlund C, 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 C, Cupido E, Fox PT, Szego K, Nemeth Z, Fedorov A, Sauvaud J-A, Koskinen H, Richter I, Lebreton J-P, Henri P, Volwerk M, Vallat C, Geiger B, 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

    , ASTRONOMY & ASTROPHYSICS, Vol: 583, Pages: A20-A20, ISSN: 1432-0746

    © 2015 ESO. The Rosetta spacecraft is escorting comet 67P/Churyumov-Gerasimenko from a heliocentric distance of > 3.6 AU, where the comet activity was low, until perihelion at 1.24 AU. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation. Using the Rosetta Plasma Consortium Ion Composition Analyzer (RPC-ICA), we study the gradual evolution of the comet ion environment, from the first detectable traces of water ions to the stage where cometary water ions accelerated to about 1 keV energy are 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 energy range. 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 h average increases by 4 orders of magnitude, mainly because high-flux periods become more common. The water ion energy spectra also become broader with time. This may indicate a larger and more uniform source region. At 2.0 AU the accelerated water ion flux is frequently of the same order as the solar wind proton flux. Water ions of 120 eV-few keV energy may thus constitute a significant part 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 nonlinear function of the heliocentric distance.
  • JOURNAL ARTICLE
    O'Reilly CH, Czaja A, O'Reilly CH, Czaja A, O'Reilly CH, Czaja Aet al., 2015,

    The response of the Pacific storm track and atmospheric circulation to Kuroshio Extension variability

    , QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Vol: 141, Pages: 52-66, ISSN: 0035-9009

    © 2014 Royal Meteorological Society. An index of the Kuroshio Extension front strength is produced using a maximum covariance analysis between sea-surface temperature (SST) and sea-surface height (SSH) gradient observations, and composites of the atmospheric state are presented during its positive and negative phases using reanalysis data (1992-2011). It is found that when the Kuroshio Extension is less (more) meandering, with a stronger (weaker) SST front, the atmospheric heat transport by transient eddies is increased in the western (eastern) Pacific region, consistent with an increase (decrease) in low-level baroclinicity. Analysis of the eddy-mean flow interaction shows that this zonal shift in heat transport forces anomalous barotropic flow in the Eastern Pacific, where blocking frequency is strongly influenced. The above relationships cannot be reconciled with the known response of the North Pacific storm track to remote forcing from the Tropical Pacific, nor can they be explained by the response of the ocean to atmospheric forcing via surface heat fluxes or winds. Rather, the zonal shift in the storm track highlighted here, and the associated changes in the large-scale circulation, are interpreted as a response to the interannual variability of the Kuroshio Extension front.

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