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  • Journal article
    Owens MJ, Horbury TS, Wicks RT, McGregor SL, Savani NP, Xiong Met al., 2014,

    Ensemble downscaling in coupled solar wind-magnetosphere modeling for space weather forecasting

    , Space Weather, Vol: 12, Pages: 395-405, ISSN: 1539-4956

    Advanced forecasting of space weather requires simulation of the whole Sun-to-Earth system, which necessitates driving magnetospheric models with the outputs from solar wind models. This presents a fundamental difficulty, as the magnetosphere is sensitive to both large-scale solar wind structures, which can be captured by solar wind models, and small-scale solar wind “noise,” which is far below typical solar wind model resolution and results primarily from stochastic processes. Following similar approaches in terrestrial climate modeling, we propose statistical “downscaling” of solar wind model results prior to their use as input to a magnetospheric model. As magnetospheric response can be highly nonlinear, this is preferable to downscaling the results of magnetospheric modeling. To demonstrate the benefit of this approach, we first approximate solar wind model output by smoothing solar wind observations with an 8 h filter, then add small-scale structure back in through the addition of random noise with the observed spectral characteristics. Here we use a very simple parameterization of noise based upon the observed probability distribution functions of solar wind parameters, but more sophisticated methods will be developed in the future. An ensemble of results from the simple downscaling scheme are tested using a model-independent method and shown to add value to the magnetospheric forecast, both improving the best estimate and quantifying the uncertainty. We suggest a number of features desirable in an operational solar wind downscaling scheme.
  • Journal article
    Hietala H, Eastwood JP, Isavnin A, 2014,

    Sequentially released tilted flux ropes in the Earth's magnetotail

    , PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 56, ISSN: 0741-3335
  • Journal article
    Miller RL, Schmidt GA, Nazarenko LS, Tausnev N, Bauer SE, DelGenio AD, Kelley M, Lo KK, Ruedy R, Shindell DT, Aleinov I, Bauer M, Bleck R, Canuto V, Chen Y, Cheng Y, Clune TL, Faluvegi G, Hansen JE, Healy RJ, Kiang NY, Koch D, Lacis AA, LeGrande AN, Lerner J, Menon S, Oinas V, Garcia-Pando CP, Perlwitz JP, Puma MJ, Rind D, Romanou A, Russell GL, Sato M, Sun S, Tsigaridis K, Unger N, Voulgarakis A, Yao M-S, Zhang Jet al., 2014,

    CMIP5 historical simulations (1850-2012) with GISS ModelE2

    , JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS, Vol: 6, Pages: 441-477
    • Cite
    • Citations: 136
  • Journal article
    Marlier ME, Voulgarakis A, Shindell DT, Faluvegi G, Henry CL, Randerson JTet al., 2014,

    The role of temporal evolution in modeling atmospheric emissions from tropical fires

    , ATMOSPHERIC ENVIRONMENT, Vol: 89, Pages: 158-168, ISSN: 1352-2310
  • Journal article
    Gryspeerdt E, Stier P, Grandey BS, 2014,

    Cloud fraction mediates the aerosol optical depth-cloud top height relationship

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 41, Pages: 3622-3627, ISSN: 0094-8276
  • Journal article
    Nichols JD, Badman SV, Baines KH, Brown RH, Bunce EJ, Clarke JT, Cowley SWH, Crary FJ, Dougherty MK, Gerard J-C, Grocott A, Grodent D, Kurth WS, Melin H, Mitchell DG, Pryor WR, Stallard TSet al., 2014,

    Dynamic auroral storms on Saturn as observed by the Hubble Space Telescope

    , Geophysical Research Letters, Vol: 41, Pages: 3323-3330, ISSN: 1944-8007

    We present observations of significant dynamics within two UV auroral storms observedon Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroralemission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ∼330%rigid corotation from near ∼01 h LT toward ∼08 h LT. We suggest that these are indicative of ongoing, burstyreconnection of lobe flux in the magnetotail, providing strong evidence that Saturn’s auroral storms arecaused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that theemission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroralform with the upward field-aligned continuity currents flowing into the associated partial ring current.
  • Journal article
    Simon S, Saur J, van Treeck SC, Kriegel H, Dougherty MKet al., 2014,

    Discontinuities in the magnetic field near Enceladus

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 41, Pages: 3359-3366, ISSN: 0094-8276
  • Journal article
    Ceppi P, Zelinka MD, Hartmann DL, 2014,

    The response of the Southern Hemispheric eddy-driven jet to future changes in shortwave radiation in CMIP5

    , Geophysical Research Letters, Vol: 41, Pages: 3244-3250, ISSN: 0094-8276

    A strong relationship is found between changes in the meridional gradient of absorbed shortwave radiation (ASR) and Southern Hemispheric jet shifts in 21st century climate simulations of CMIP5 (Coupled Model Intercomparison Project phase 5) coupled models. The relationship is such that models with increases in the meridional ASR gradient around the southern midlatitudes, and therefore increases in midlatitude baroclinicity, tend to produce a larger poleward jet shift. The ASR changes are shown to be dominated by changes in cloud properties, with sea ice declines playing a secondary role. We demonstrate that the ASR changes are the cause, and not the result, of the intermodel differences in jet response by comparing coupled simulations with experiments in which sea surface temperature increases are prescribed. Our results highlight the importance of reducing the uncertainty in cloud feedbacks in order to constrain future circulation changes.
  • Book chapter
    Galand MIF, Coates A, Cravens T, Wahlund J-Eet al., 2014,

    Titan's Ionosphere

    , Titan: Interior, Surface, Atmosphere, and Space Environment, Editors: Mueller-Wodarg, Griffith, Lellouch, Cravens, Publisher: Cambridge University Press, Pages: 376-418, ISBN: 9780521199926
  • Journal article
    Vigren E, Galand M, Shebanits O, Wahlund J-E, Geppert WD, Lavvas P, Vuitton V, Yelle RVet al., 2014,

    INCREASING POSITIVE ION NUMBER DENSITIES BELOW THE PEAK OF ION-ELECTRON PAIR PRODUCTION IN TITAN'S IONOSPHERE

    , ASTROPHYSICAL JOURNAL, Vol: 786, ISSN: 0004-637X
    • Cite
    • Citations: 10
  • Journal article
    Southwood D, 2014,

    Crowded Orbits: Conflict and Cooperation in Space

    , NATURE, Vol: 509, Pages: 32-32, ISSN: 0028-0836
  • Journal article
    Bunce EJ, Grodent DC, Jinks SL, Andrews DJ, Badman SV, Coates AJ, Cowley SWH, Dougherty MK, Kurth WS, Mitchell DG, Provan Get al., 2014,

    Cassini nightside observations of the oscillatory motion of Saturn's northern auroral oval

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 3528-3543, ISSN: 2169-9380
  • Journal article
    Ansell C, Brindley HE, Pradhan Y, Saunders Ret al., 2014,

    Mineral dust aerosol net direct radiative effect during GERBILS field campaign period derived from SEVIRI and GERB

    , JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 119, Pages: 4070-4086, ISSN: 2169-897X
  • Journal article
    Goldman MV, Newman DL, Lapenta G, Andersson L, Gosling JT, Eriksson S, Markidis S, Eastwood JP, Ergun Ret al., 2014,

    Cerenkov Emission of Quasiparallel Whistlers by Fast Electron Phase-Space Holes during Magnetic Reconnection

    , PHYSICAL REVIEW LETTERS, Vol: 112, ISSN: 0031-9007
  • Journal article
    Badman SV, Branduardi-Raymont G, Galand M, Hess SLG, Krupp N, Lamy L, Melin H, Tao Cet al., 2014,

    Auroral Processes at the Giant Planets: Energy Deposition, Emission Mechanisms, Morphology and Spectra

    , Space Science Reviews, Vol: 187, Pages: 99-179, ISSN: 1572-9672

    The ionospheric response to auroral precipitation at the giant planets is reviewed,using models and observations. The emission processes for aurorae at radio, infrared, visible,ultraviolet, and X-ray wavelengths are described, and exemplified using ground- andspace-based observations. Comparisons between the emissions at different wavelengths are made, where possible, and interpreted in terms of precipitating particle characteristics oratmospheric conditions. Finally, the spatial distributions and dynamics of the various componentsof the aurorae (moon footprints, low-latitude, main oval, polar) are related to magnetosphericprocesses and boundaries, using theory, in situ, and remote observations, withthe aim of distinguishing between those related to internally-driven dynamics, and thoserelated to the solar wind interaction.
  • Journal article
    Messori G, Czaja A, 2014,

    Some considerations on the spectral features of meridional heat transport by transient eddies

    , QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Vol: 140, Pages: 1377-1386, ISSN: 0035-9009
  • Journal article
    Shen C, Yang YY, Rong ZJ, Li X, Dunlop M, Carr CM, Liu ZX, Baker DN, Chen ZQ, Ji Y, Zeng Get al., 2014,

    Direct calculation of the ring current distribution and magnetic structure seen by Cluster during geomagnetic storms

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 2458-2465, ISSN: 2169-9380
    • Cite
    • Citations: 36
  • Journal article
    Fuselier SA, Frahm R, Lewis WS, Masters A, Mukherjee J, Petrinec SM, Sillanpaa IJet al., 2014,

    The location of magnetic reconnection at Saturn's magnetopause: A comparison with Earth

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 2563-2578, ISSN: 2169-9380
  • Journal article
    Pilkington NM, Achilleos N, Arridge CS, Masters A, Sergis N, Coates AJ, Dougherty MKet al., 2014,

    Polar confinement of Saturn's magnetosphere revealed by in situ Cassini observations

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 2858-2875, ISSN: 2169-9380
  • Journal article
    Kriegel H, Simon S, Meier P, Motschmann U, Saur J, Wennmacher A, Strobel DF, Dougherty MKet al., 2014,

    Ion densities and magnetic signatures of dust pickup at Enceladus

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 2740-2774, ISSN: 2169-9380
  • Journal article
    Meredith CJ, Alexeev II, Badman SV, Belenkaya ES, Cowley SWH, Dougherty MK, Kalegaev VV, Lewis GR, Nichols JDet al., 2014,

    Saturn's dayside ultraviolet auroras: Evidence for morphological dependence on the direction of the upstream interplanetary magnetic field

    , Journal of Geophysical Research: Space Physics, Vol: 119, Pages: 1994-2008, ISSN: 2169-9402

    We examine a unique data set from seven Hubble Space Telescope (HST) “visits” that imagedSaturn’s northern dayside ultraviolet emissions exhibiting usual circumpolar “auroral oval” morphologies,during which Cassini measured the interplanetary magnetic field (IMF) upstream of Saturn’s bow shock overintervals of several hours. The auroras generally consist of a dawn arc extending toward noon centered near~15° colatitude, together with intermittent patchy forms at ~10° colatitude and poleward thereof, locatedbetween noon and dusk. The dawn arc is a persistent feature, but exhibits variations in position, width, andintensity, which have no clear relationship with the concurrent IMF. However, the patchy postnoon aurorasare found to relate to the (suitably lagged and averaged) IMF Bz, being present during all four visits withpositive Bz and absent during all three visits with negative Bz. The most continuous such forms occur in thecase of strongest positive Bz. These results suggest that the postnoon forms are associated with reconnectionand open flux production at Saturn’s magnetopause, related to the similarly interpreted bifurcated auroral arcstructures previously observed in this local time sector in Cassini Ultraviolet Imaging Spectrograph data,whose details remain unresolved in these HST images. One of the intervals with negative IMF Bz howeverexhibits a prenoon patch of very high latitude emission extending poleward of the dawn arc to the magnetic/spin pole, suggestive of the occurrence of lobe reconnection. Overall, these data provide evidence ofsignificant IMF dependence in the morphology of Saturn’s dayside auroras.
  • Journal article
    Masters A, Fujimoto M, Hasegawa H, Russell CT, Coates AJ, Dougherty MKet al., 2014,

    Can magnetopause reconnection drive Saturn's magnetosphere?

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 41, Pages: 1862-1868, ISSN: 0094-8276
    • Cite
    • Citations: 23
  • Journal article
    Cargill PJ, 2014,

    ACTIVE REGION EMISSION MEASURE DISTRIBUTIONS AND IMPLICATIONS FOR NANOFLARE HEATING

    , ASTROPHYSICAL JOURNAL, Vol: 784, ISSN: 0004-637X
  • Journal article
    Jasinski JM, Arridge CS, Lamy L, Leisner JS, Thomsen MF, Mitchell DG, Coates AJ, Radioti A, Jones GH, Roussos E, Krupp N, Grodent D, Dougherty MK, Waite JHet al., 2014,

    Cusp observation at Saturn's high-latitude magnetosphere by the Cassini spacecraft

    , Geophysical Research Letters, Vol: 41, Pages: 1382-1388, ISSN: 1944-8007

    We report on the first analysis of magnetospheric cusp observations at Saturn by multiple insitu instruments onboard the Cassini spacecraft. Using this we infer the process of reconnection wasoccurring at Saturn’s magnetopause. This agrees with remote observations that showed the associatedauroral signatures of reconnection. Cassini crossed the northern cusp around noon local time along apoleward trajectory. The spacecraft observed ion energy-latitude dispersions—a characteristic signature ofthe terrestrial cusp. This ion dispersion is “stepped,” which shows that the reconnection is pulsed. The ionenergy-pitch angle dispersions suggest that the field-aligned distance from the cusp to the reconnectionsite varies between ∼27 and 51 RS. An intensification of lower frequencies of the Saturn kilometricradiation emissions suggests the prior arrival of a solar wind shock front, compressing the magnetosphereand providing more favorable conditions for magnetopause reconnection.
  • Journal article
    Hartmann DL, Ceppi P, 2014,

    Trends in the CERES dataset, 2000-13: the effects of sea ice and jet shifts and comparison to climate models

    , Journal of Climate, Vol: 27, Pages: 2444-2456, ISSN: 0894-8755

    The Clouds and the Earth’s Radiant Energy System (CERES) observations of global top-of-atmosphere radiative energy fluxes for the period March 2000–February 2013 are examined for robust trends and variability. The trend in Arctic ice is clearly evident in the time series of reflected shortwave radiation, which closely follows the record of ice extent. The data indicate that, for every 106 km2 decrease in September sea ice extent, annual-mean absorbed solar radiation averaged over 75°–90°N increases by 2.5 W m−2, or about 6 W m−2 between 2000 and 2012. CMIP5 models generally show a much smaller change in sea ice extent over the 1970–2012 period, but the relationship of sea ice extent to reflected shortwave is in good agreement with recent observations. Another robust trend during this period is an increase in reflected shortwave radiation in the zonal belt from 45° to 65°S. This trend is mostly related to increases in sea ice concentrations in the Southern Ocean and less directly related to cloudiness trends associated with the annular variability of the Southern Hemisphere. Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) produce a scaling of cloud reflection to zonal wind increase that is similar to trend observations in regions separated from the direct effects of sea ice. Atmospheric Model Intercomparison Project (AMIP) model responses over the Southern Ocean are not consistent with each other or with the observed shortwave trends in regions removed from the direct effect of sea ice.
  • Journal article
    Southwood DJ, Cowley SWH, 2014,

    The origin of Saturn's magnetic periodicities: Northern and southern current systems

    , Journal of Geophysical Research: Space Physics, Vol: 119, Pages: 1563-1571, ISSN: 2169-9380

    The recent survey by Andrews et al. (2012) of the separate northern and southern ~10.7 h periodic magnetic signals in Saturn's magnetosphere limits very much their governing current systems. The existence of signals with pure or close to pure northern or southern periods in respective polar caps taken with the relatively narrow bandwidth of the signals indicates that the actual periodicities are imposed independently from northern and southern polar regions, i.e., the open field line regions. Field‐aligned currents must flow on the boundaries of these regions to exclude signals from the other hemisphere. Equatorward of the polar cap, on closed magnetic shells, there are distinct north and south “cam” source currents, the distinction being made clear by a difference in polarization. We outline the consequences for the governing current systems and the implications for sustaining the energy and power dissipation in the system.
  • Journal article
    Mistry R, Dougherty MK, Masters A, Sulaiman AH, Allen EJet al., 2014,

    Separating drivers of Saturnian magnetopause motion

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 1514-1522, ISSN: 2169-9380
  • Journal article
    Liu YD, Luhmann JG, Kajdic P, Kilpua EKJ, Lugaz N, Nitta NV, Moestl C, Lavraud B, Bale SD, Farrugia CJ, Galvin ABet al., 2014,

    Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections

    , NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723
    • Cite
    • Citations: 251
  • Journal article
    Schwartz SJ, 2014,

    Comment on "Electron demagnetization and heating in quasi-perpendicular shocks" by Mozer and Sundkvist

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 1507-1512, ISSN: 2169-9380
  • Journal article
    Schmidt GA, Kelley M, Nazarenko L, Ruedy R, Russell GL, Aleinov I, Bauer M, Bauer SE, Bhat MK, Bleck R, Canuto V, Chen Y-H, Cheng Y, Clune TL, Del Genio A, de Fainchtein R, Faluvegi G, Hansen JE, Healy RJ, Kiang NY, Koch D, Lacis AA, LeGrande AN, Lerner J, Lo KK, Matthews EE, Menon S, Miller RL, Oinas V, Oloso AO, Perlwitz JP, Puma MJ, Putman WM, Rind D, Romanou A, Sato M, Shindell DT, Sun S, Syed RA, Tausnev N, Tsigaridis K, Unger N, Voulgarakis A, Yao M-S, Zhang Jet al., 2014,

    Configuration and assessment of the GISS ModelE2 contributions to the CMIP5 archive

    , JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS, Vol: 6, Pages: 141-184

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