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  • Journal article
    Kilpua EKJ, Good SW, Palmerio E, Asvestari E, Lumme E, Ala-Lahti M, Kalliokoski MMH, Morosan DE, Pomoell J, Price DJ, Magdalenic J, Poedts S, Futaana Yet al., 2019,

    Multipoint Observations of the June 2012 Interacting Interplanetary Flux Ropes

    , FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, Vol: 6, ISSN: 2296-987X
  • Journal article
    Sillmann J, Stjern CW, Myhre G, Samset BH, Hodnebrog O, Andrews T, Boucher O, Faluvegi G, Forster P, Kasoar MR, Kharin VV, Kirkevag A, Lamarque J-F, Olivie DJL, Richardson TB, Shindell D, Takemura T, Voulgarakis A, Zwiers FWet al., 2019,

    Extreme wet and dry conditions affected differently by greenhouse gases and aerosols

    , npj Climate and Atmospheric Science, Vol: 2, Pages: 1-7, ISSN: 2397-3722

    Global warming due to greenhouse gases and atmospheric aerosols alter precipitation rates, but the influence on extreme precipitation by aerosols relative to greenhouse gases is still not well known. Here we use the simulations from the Precipitation Driver and Response Model Intercomparison Project that enable us to compare changes in mean and extreme precipitation due to greenhouse gases with those due to black carbon and sulfate aerosols, using indicators for dry extremes as well as for moderate and very extreme precipitation. Generally, we find that the more extreme a precipitation event is, the more pronounced is its response relative to global mean surface temperature change, both for aerosol and greenhouse gas changes. Black carbon (BC) stands out with distinct behavior and large differences between individual models. Dry days become more frequent with BC-induced warming compared to greenhouse gases, but so does the intensity and frequency of extreme precipitation. An increase in sulfate aerosols cools the surface and thereby the atmosphere, and thus induces a reduction in precipitation with a stronger effect on extreme than on mean precipitation. A better understanding and representation of these processes in models will provide knowledge for developing strategies for both climate change and air pollution mitigation.
  • Journal article
    Stjern CW, Lund MT, Samset BH, Myhre G, Forster PM, Andrews T, Boucher O, Faluvegi G, Flaeschner D, Iversen T, Kasoar M, Kharin V, Kirkevag A, Lamarque J-F, Olivie D, Richardson T, Sand M, Shawki D, Shindell D, Smith CJ, Takemura T, Voulgarakis Aet al., 2019,

    Arctic amplification response to individual climate drivers

    , Journal of Geophysical Research: Atmospheres, Vol: 124, Pages: 6698-6717, ISSN: 2169-897X

    The Arctic is experiencing rapid climate change in response to changes in greenhouse gases, aerosols, and other climate drivers. Emission changes in general, as well as geographical shifts in emissions and transport pathways of short‐lived climate forcers, make it necessary to understand the influence of each climate driver on the Arctic. In the Precipitation Driver Response Model Intercomparison Project, 10 global climate models perturbed five different climate drivers separately (CO2, CH4, the solar constant, black carbon, and SO4). We show that the annual mean Arctic amplification (defined as the ratio between Arctic and the global mean temperature change) at the surface is similar between climate drivers, ranging from 1.9 (± an intermodel standard deviation of 0.4) for the solar to 2.3 (±0.6) for the SO4 perturbations, with minimum amplification in the summer for all drivers. The vertical and seasonal temperature response patterns indicate that the Arctic is warmed through similar mechanisms for all climate drivers except black carbon. For all drivers, the precipitation change per degree global temperature change is positive in the Arctic, with a seasonality following that of the Arctic amplification. We find indications that SO4 perturbations produce a slightly stronger precipitation response than the other drivers, particularly compared to CO2.
  • Journal article
    Sulaiman AH, Farrell WM, Ye S-Y, Kurth WS, Gurnett DA, Hospodarsky GB, Menietti JD, Pisa D, Hunt GJ, Agiwal O, Dougherty MKet al., 2019,

    A Persistent, Large-Scale, and Ordered Electrodynamic Connection Between Saturn and Its Main Rings

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 7166-7172, ISSN: 0094-8276
  • Journal article
    Pitna A, Safrankova J, Nemecek Z, Franci L, Pi G, Camps VMet al., 2019,

    Characteristics of Solar Wind Fluctuations at and below Ion Scales

    , ASTROPHYSICAL JOURNAL, Vol: 879, ISSN: 0004-637X
  • Journal article
    AkhavanTafti M, Slavin JA, Eastwood JP, Cassak PA, Gershman DJet al., 2019,

    MMS multi‐point analysis of FTE evolution: physical characteristics and dynamics

    , Journal of Geophysical Research: Space Physics, Vol: 124, Pages: 5376-5395, ISSN: 2169-9380

    Previous studies have indicated that flux transfer events (FTEs) grow as they convect away from the reconnection site along the magnetopause. This increase in FTE diameter may occur via adiabatic expansion in response to decreasing external pressure away from the subsolar region or due to a continuous supply of magnetic flux and plasma to the FTEs' outer layers by magnetic reconnection. Here we investigate an ensemble of 55 FTEs at the subsolar magnetopause using Magnetospheric Multiscale (MMS) multi‐point measurements. The FTEs are initially modeled as quasi‐force‐free flux ropes in order to infer their geometry and the spacecraft trajectory relative to their central axis. The MMS observations reveal a radially‐inward net force at the outer layers of FTEs which can accelerate plasmas and fields toward the FTE's core region. Inside the FTEs, near the central axis, plasma density is found to decrease as the axial net force increases. It is interpreted that the axial net force accelerates plasmas along the axis in the region of compressing field lines. Statistical analysis of the MMS observations of the 55 FTEs indicates that plasma pressure, Pth, decreases with increasing FTE diameter, λ, as Pth,obsv ∝ λ−0.24. Assuming that all 55 FTEs started out with similar diameters, this rate of plasma pressure decrease with increasing FTE diameter is at least an order of magnitude slower than the theoretical rate for adiabatic expansion (i.e., Pth,adiab. ∝ λ−3.3), suggesting the presence of efficient plasma heating mechanisms, such as magnetic reconnection, to facilitate FTE growth.
  • Journal article
    Palmroth M, Praks J, Vainio R, Janhunen P, Kilpua EKJ, Afanasiev A, Ala-Lahti M, Alho A, Asikainen T, Asvestari E, Battarbee M, Binios A, Bosser A, Brito T, Dubart M, Envall J, Ganse U, Ganushkina NY, George H, Gieseler J, Good S, Grandin M, Haslam S, Hedman H-P, Hietala H, Jovanovic N, Kakakhel S, Kalliokoski M, Kettunen VV, Koskela T, Lumme E, Meskanen M, Morosan D, Mughal MR, Niemela P, Nyman S, Oleynik P, Osmane A, Palmerio E, Peltonen J, Pfau-Kempf Y, Plosila J, Polkko J, Poluianov S, Pomoell J, Price D, Punkkinen A, Punkkinen R, Riwanto B, Salomaa L, Slavinskis A, Santti T, Tammi J, Tenhunen H, Toivanen P, Tuominen J, Turc L, Valtonen E, Virtanen P, Westerlund Tet al., 2019,

    FORESAIL-1 CubeSat Mission to Measure Radiation Belt Losses and Demonstrate Deorbiting

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 5783-5799
  • Journal article
    Lavergne A, Graven H, De Kauwe MG, Keenan FT, Medlyn BE, Prentice Iet al., 2019,

    Observed and modelled historical trends in the water use efficiency of plants and ecosystems

    , Global Change Biology, Vol: 25, Pages: 2242-2257, ISSN: 1354-1013

    Plant water‐use efficiency (WUE, the carbon gained through photosynthesis per unit of water lost through transpiration) is a tracer of the plant physiological controls on the exchange of water and carbon dioxide between terrestrial ecosystems and the atmosphere. At the leaf level, rising CO2 concentrations tend to increase carbon uptake (in the absence of other limitations) and to reduce stomatal conductance, both effects leading to an increase in leaf WUE. At the ecosystem level, indirect effects (e.g. increased leaf area index, soil water savings) may amplify or dampen the direct effect of CO2. Thus, the extent to which changes in leaf WUE translate to changes at the ecosystem scale remains unclear. The differences in the magnitude of increase in leaf versus ecosystem WUE as reported by several studies are much larger than would be expected with current understanding of tree physiology and scaling, indicating unresolved issues. Moreover, current vegetation models produce inconsistent and often unrealistic magnitudes and patterns of variability in leaf and ecosystem WUE, calling for a better assessment of the underlying approaches. Here, we review the causes of variations in observed and modelled historical trends in WUE over the continuum of scales from leaf to ecosystem, including methodological issues, with the aim of elucidating the reasons for discrepancies observed within and across spatial scales. We emphasize that even though physiological responses to changing environmental drivers should be interpreted differently depending on the observational scale, there are large uncertainties in each data set which are often underestimated. Assumptions made by the vegetation models about the main processes influencing WUE strongly impact the modelled historical trends. We provide recommendations for improving long‐term observation‐based estimates of WUE that will better inform the representation of WUE in vegetation models.
  • Journal article
    Hall RJ, Wei H-L, Hanna E, 2019,

    Complex systems modelling for statistical forecasting of winter North Atlantic atmospheric variability: A new approach to North Atlantic seasonal forecasting

    , QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Vol: 145, Pages: 2568-2585, ISSN: 0035-9009
  • Journal article
    Wilson LB, Chen L-J, Wang S, Schwartz SJ, Turner DL, Stevens ML, Kasper JC, Osmane A, Caprioli D, Bale SD, Pulupa MP, Salem CS, Goodrich KAet al., 2019,

    Electron Energy Partition across Interplanetary Shocks. I. Methodology and Data Product

    , ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 243, ISSN: 0067-0049
  • Journal article
    Good SW, Kilpua EKJ, LaMoury AT, Forsyth RJ, Eastwood JP, Möstl Cet al., 2019,

    Self‐similarity of ICME flux ropes: Observations by radially aligned spacecraft in the inner Heliosphere

    , Journal of Geophysical Research: Space Physics, Vol: 124, Pages: 4960-4982, ISSN: 2169-9380

    Interplanetary coronal mass ejections (ICMEs) are a significant feature of the heliospheric environment and the primary cause of adverse space weather at the Earth. ICME propagation and the evolution of ICME magnetic field structure during propagation are still not fully understood. We analyze the magnetic field structures of 18 ICME magnetic flux ropes observed by radially aligned spacecraft in the inner heliosphere. Similarity in the underlying flux rope structures is determined through the application of a simple technique that maps the magnetic field profile from one spacecraft to the other. In many cases, the flux ropes show very strong underlying similarities at the different spacecraft. The mapping technique reveals similarities that are not readily apparent in the unmapped data and is a useful tool when determining whether magnetic field time series observed at different spacecraft are associated with the same ICME. Lundquist fitting has been applied to the flux ropes, and the rope orientations have been determined; macroscale differences in the profiles at the aligned spacecraft may be ascribed to differences in flux rope orientation. Assuming that the same region of the ICME was observed by the aligned spacecraft in each case, the fitting indicates some weak tendency for the rope axes to reduce in inclination relative to the solar equatorial plane and to align with the solar east‐west direction with heliocentric distance.Plain Language SummaryCoronal mass ejections (CMEs) are large eruptions of magnetic field and plasma from the Sun. When they arrive at the Earth, these eruptions can cause significant damage to ground and orbital infrastructure; forecasting this “space weather” impact of CMEs at the Earth remains a difficult task. The impact of individual CMEs is largely dependent on their magnetic field configurations, and an important aspect of space weather forecasting is understanding how CME field configuration changes with distance from t
  • Journal article
    Kronberg EA, Grigorenko EE, Malykhin A, Kozak L, Petrenko B, Vogt M, Roussos E, Kollmann P, Jackman C, Kasahara S, Malova KV, Tao C, Radioti A, Masters Aet al., 2019,

    Acceleration of ions in Jovian plasmoids: does turbulence play a role?

    , Journal of Geophysical Research: Space Physics, Vol: 124, Pages: 5056-5069, ISSN: 2169-9380

    The dissipation processes which transform electromagnetic energy into kinetic particle energy in space plasmas are still not fully understood. Of particular interest is the distribution of the dissipated energy among different species of charged particles. The Jovian magnetosphere is a unique laboratory to study this question because outflowing ions from the moon Io create a high diversity in ion species. In this work, we use multispecies ion observations and magnetic field measurements by the Galileo spacecraft. We limit our study to observations of plasmoids in the Jovian magnetotail, because there is strong ion acceleration in these structures. Our model predicts that electromagnetic turbulence in plasmoids plays an essential role in the acceleration of oxygen, sulfur, and hydrogen ions. The observations show a decrease of the oxygen and sulfur energy spectral index γ at ∼30 to ∼400 keV/nuc with the wave power indicating an energy transfer from electromagnetic waves to particles, in agreement with the model. The wave power threshold for effective acceleration is of the order of 10 nT2Hz−1, as in terrestrial plasmoids. However, this is not observed for hydrogen ions, implying that processes other than wave‐particle interaction are more important for the acceleration of these ions or that the time and energy resolution of the observations is too coarse. The results are expected to be confirmed by improved plasma measurements by the Juno spacecraft.
  • Journal article
    Shi J, Zhang Z, Torkar K, Cheng Z, Escoubet P, Farzakeley A, Dunlop M, Carr Cet al., 2019,

    South‐North Hemispheric Asymmetry of the FAE Distribution Around the Cusp Region: Cluster Observation

    , Journal of Geophysical Research: Space Physics, Vol: 124, Pages: 5342-5352, ISSN: 2169-9380

    Cluster data from late July to early October were used to study the distribution of field‐aligned electron (FAE) events around the two cusps. An FAE event was defined as electron parallel flux >3 × 108 (cm2 s)−1. The total number of FAE events around the two cusps was basically identical, but downward FAE events prevailed in the south and upward FAE events in the north. In the southern cusp, the peak of the FAE events distribution versus altitude was about 1.3 RE higher and the peak of the FAE events distribution versus invariant latitude (ILAT) was about 4° ILAT lower. Only the downward FAEs around the southern cusp had a second ILAT peak, which was located about 11° higher than the main peak. The normalized number of FAEs showed nearly the same features as the unnormalized number of the FAEs events. These results indicated a north‐south asymmetry of the FAE distribution around the two cusps. Some causes for the asymmetry are discussed, the main ones being the asymmetry of the magnetospheric configuration resulting from geomagnetic dipolar tilt and solar wind flows, the interplanetary magnetic field asymmetry related to the magnetosphere, and the difference of ionospheric conductivity in the two hemispheres. Various solar wind‐magnetosphere interaction processes, such as quasi‐viscous interaction and reconnection, are responsible for the asymmetry, too. The second distribution peak (at higher ILAT) of the downward FAE events around the southern cusp corresponded to high solar wind speed and may be associated with the northward interplanetary magnetic field Bz field‐aligned current at low altitude. This requires further studies, however.
  • Journal article
    Verdini A, Grappin R, Alexandrova O, Franci L, Landi S, Matteini L, Papini Eet al., 2019,

    Three-dimensional local anisotropy of velocity fluctuations in the solar wind

    , MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 486, Pages: 3006-3018, ISSN: 0035-8711
  • Journal article
    Ceppi P, Shepherd TG, 2019,

    The role of the stratospheric polar vortex for the austral jet response to greenhouse gas forcing

    , Geophysical Research Letters, Vol: 46, Pages: 6972-6979, ISSN: 0094-8276

    Future shifts of the austral midlatitude jet are subject to large uncertainties in climate model projections. Here we show that, in addition to other previously identified sources of intermodel uncertainty, changes in the timing of the stratospheric polar vortex breakdown modulate the austral jet response to greenhouse gas forcing during summertime (December–February). The relationship is such that a larger delay in vortex breakdown favors a more poleward jet shift, with an estimated 0.7–0.8° increase in jet shift per 10-day delay in vortex breakdown. The causality of the link between the timing of the vortex breakdown and the tropospheric jet response is demonstrated through climate modeling experiments with imposed changes in the seasonality of the stratospheric polar vortex. The vortex response is estimated to account for about 30% of the intermodel variance in the shift of the summertime austral jet and about 45% of the mean jet shift.
  • Journal article
    Cravens TE, Moore L, Waite JH, Perryman R, Perry M, Wahlund J-E, Persoon A, Kurth WSet al., 2019,

    The Ion Composition of Saturn's Equatorial Ionosphere as Observed by Cassini

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 6315-6321, ISSN: 0094-8276
  • Journal article
    Bellisario C, Brindley HE, Tett SFB, Rizzi R, Di Natale G, Palchetti L, Bianchini Get al., 2019,

    Can downwelling far-infrared radiances over Antarctica be estimated from mid-infrared information?

    , Atmospheric Chemistry and Physics, Vol: 19, Pages: 7927-7937, ISSN: 1680-7316

    Far-infrared (FIR: 100cm−1<wavenumber, ν<667 cm−1) radiation emitted by the Earth and its atmosphere plays a key role in the Earth's energy budget. However, because of a lack of spectrally resolved measurements, radiation schemes in climate models suffer from a lack of constraint across this spectral range. Exploiting a method developed to estimate upwelling far-infrared radiation from mid-infrared (MIR: 667cm−1<ν<1400 cm−1) observations, we explore the possibility of inferring zenith FIR downwelling radiances in zenith-looking observation geometry, focusing on clear-sky conditions in Antarctica. The methodology selects a MIR predictor wavenumber for each FIR wavenumber based on the maximum correlation seen between the different spectral ranges. Observations from the REFIR-PAD instrument (Radiation Explorer in the Far Infrared – Prototype for Application and Development) and high-resolution radiance simulations generated from co-located radio soundings are used to develop and assess the method. We highlight the impact of noise on the correlation between MIR and FIR radiances by comparing the observational and theoretical cases. Using the observed values in isolation, between 150 and 360 cm−1, differences between the “true” and “extended” radiances are less than 5 %. However, in spectral bands of low signal, between 360 and 667 cm−1, the impact of instrument noise is strong and increases the differences seen. When the extension of the observed spectra is performed using regression coefficients based on noise-free radiative transfer simulations the results show strong biases, exceeding 100 % where the signal is low. These biases are reduced to just a few percent if the noise in the observations is accounted for in the simulation procedure. Our results imply that while it is feasible to use this type of approach to extend mid-infrared spectral m
  • Journal article
    Mallet A, Klein KG, Chandran BDG, Groselj D, Hoppock IW, Bowen TA, Salem CS, Bale SDet al., 2019,

    Interplay between intermittency and dissipation in collisionless plasma turbulence

    , JOURNAL OF PLASMA PHYSICS, Vol: 85, ISSN: 0022-3778
  • Journal article
    Palmerio E, Scolini C, Barnes D, Magdalenic J, West MJ, Zhukov AN, Rodriguez L, Mierla M, Good SW, Morosan DE, Kilpua EKJ, Pomoell J, Poedts Set al., 2019,

    Multipoint Study of Successive Coronal Mass Ejections Driving Moderate Disturbances at 1 au

    , ASTROPHYSICAL JOURNAL, Vol: 878, ISSN: 0004-637X
  • Journal article
    Tong Y, Vasko IY, Artemyev A, Bale SD, Mozer FSet al., 2019,

    Statistical Study of Whistler Waves in the Solar Wind at 1 au

    , ASTROPHYSICAL JOURNAL, Vol: 878, ISSN: 0004-637X
  • Journal article
    Stawarz J, Eastwood JP, Phan TD, Gingell IL, Shay MA, Burch JL, Ergun RE, Giles BL, Gershman DJ, Le Contel O, Lindqvist P-A, Russell CT, Strangeway RJ, Torbert RB, Argall MR, Fischer D, Magnes W, Franci Let al., 2019,

    Properties of the turbulence associated with electron-only magnetic reconnection in Earth's magnetosheath

    , Letters of the Astrophysical Journal, Vol: 877, ISSN: 2041-8205

    Turbulent plasmas generate intense current structures, which have long been suggested as magnetic reconnection sites. Recent Magnetospheric Multiscale observations in Earth's magnetosheath revealed a novel form of reconnection where the dynamics only couple to electrons, without ion involvement. It was suggested that such dynamics were driven by magnetosheath turbulence. In this study, the fluctuations are examined to determine the properties of the turbulence and if a signature of reconnection is present in the turbulence statistics. The study reveals statistical properties consistent with plasma turbulence with a correlation length of ~10 ion inertial lengths. When reconnection is more prevalent, a steepening of the magnetic spectrum occurs at the length scale of the reconnecting current sheets. The statistics of intense currents suggest the prevalence of electron-scale current sheets favorable for electron reconnection. The results support the hypothesis that electron reconnection is driven by turbulence and highlight diagnostics that may provide insight into reconnection in other turbulent plasmas.
  • Journal article
    Cohen IJ, Schwartz SJ, Goodrich KA, Ahmadi N, Ergun RE, Fuselier SA, Desai M, Christian ER, McComas DJ, Zank GP, Shuster JR, Vines SK, Mauk BH, Decker RB, Anderson BJ, Westlake JH, Le Contel O, Breuillard H, Giles BL, Torbert RB, Burch JLet al., 2019,

    High-Resolution Measurements of the Cross-Shock potential, Ion Reflection, and Electron Heating at an Interplanetary Shock by MMS

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 3961-3978, ISSN: 2169-9380
  • Journal article
    Liu F, Fiencke C, Guo J, Lyu T, Dong R, Pfeiffer E-Met al., 2019,

    Optimisation of bioscrubber systems to simultaneously remove methane and purify wastewater from intensive pig farms

    , Environmental Science and Pollution Research, Vol: 26, Pages: 15847-15856, ISSN: 0944-1344
  • Journal article
    wang S, Toumi R, 2019,

    Impact of dry midlevel air on the tropical cyclone outer circulation

    , Journal of the Atmospheric Sciences, Vol: 76, Pages: 1809-1826, ISSN: 0022-4928

    The impact of dry midlevel air on the outer circulation of tropical cyclones is investigated in idealized simulations with and without a moist envelope protecting the inner core. It is found that a dry midlevel layer away from the cyclone center can broaden the outer primary circulation and thus the overall destructive potential at both developing and mature stages. The midlevel outer drying enhances the horizontal gradient of latent heating in the rainbands and drives the expansion of the outer circulation. The moist convection at large radii is suppressed rapidly after the midlevel air is dried in the outer rainbands. An enhanced horizontal gradient of latent heating initiates a radial-vertical overturning circulation anomaly in the rainbands. This anomalous overturning circulation accelerates the radial inflow of the main secondary circulation, increases the angular momentum import, and thus increases the cyclone size. The dry air, mixed into the boundary layer from the midtroposphere, is “recharged” by high enthalpy fluxes due to the increased thermodynamical disequilibrium above the sea surface. This “recharge” process protects the eyewall convection from the environmental dry air ventilation. The proposed mechanism may explain the continuous expansion in the tropical cyclone outer circulation after maturity as found in observations.
  • Journal article
    Lasslop G, Coppola A, Voulgarakis A, Yue C, Veraverbeke Set al., 2019,

    Influence of Fire on the Carbon Cycle and Climate

    , CURRENT CLIMATE CHANGE REPORTS, Vol: 5, Pages: 112-123, ISSN: 2198-6061
  • Journal article
    Matteini L, Stansby D, Horbury TS, Chen CHKet al., 2019,

    The rotation angle distribution underlying magnetic field fluctuations in the 1/f range of solar wind turbulent spectra

    , Il Nuovo Cimento C – Colloquia and Communications in Physics, Vol: 42, ISSN: 2037-4909

    We discuss properties of large amplitude magnetic field fluctuationsduring fast Alfv ́eenic solar wind streams, focussing on the statistics of the rotationangle between consecutive magnetic field vector measurements for different scalesin the plasma. Since in the fast solar wind fluctuations preserve the modulus ofthe magnetic field to a good approximation, the tip of the magnetic field vector isobserved to move on a sphere of approximately constant radius|B|.Wethencom-pare statistics of solar wind measurements with that of a simple model of a randomwalk bounded on a spherical surface. The analogy consists in the fact that in bothsystems the geometrical constraint imposes a limiting amplitude at large separa-tions and thus introduces a break scale in the power spectrum of the fluctuations,leading to a shallower slope for scales where the fluctuations amplitude becomesscale-independent. However, while in the case of the random walk the saturationof the fluctuations occurs when the pattern becomes uniform on the sphere (flatdistribution of the cosine of the rotation angle), transitioning then to a white noiseregime, in the solar wind magnetic field fluctuations saturate in amplitude maintain-ing a preferential direction. We suggest that this behaviour is due to the presence ofthe background interplanetary magnetic field, which keeps some long-range memoryin the system also when the fluctuations becomes independent of the scale. Thislong-range correlation is a necessary ingredient in order to produce the 1/fspectrumobserved at large scales in the solar wind.
  • Journal article
    Johnston C, Cargill P, antolin P, hood A, de moortel I, Bradshaw Set al., 2019,

    The effects of numerical resolution, heating timescales and background heating on thermal non-equilibrium in coronal loops

    , Astronomy and Astrophysics, Vol: 625, ISSN: 0004-6361

    Thermal non-equilibrium (TNE) is believed to be a potentially important process in understanding some properties ofthe magnetically closed solar corona. Through one-dimensional hydrodynamic models, this paper addresses the importanceof the numerical spatial resolution, footpoint heating timescales and background heating on TNE. Inadequatetransition region (TR) resolution can lead to significant discrepancies in TNE cycle behaviour, with TNE being suppressedin under-resolved loops. A convergence on the periodicity and plasma properties associated with TNE requiredspatial resolutions of less than 2 km for a loop of length 180 Mm. These numerical problems can be resolved using anapproximate method that models the TR as a discontinuity using a jump condition, as proposed by Johnston et al.(2017a,b). The resolution requirements (and so computational cost) are greatly reduced while retaining good agreementwith fully resolved results. Using this approximate method we (i) identify different regimes for the response of coronalloops to time-dependent footpoint heating including one where TNE does not arise and (ii) demonstrate that TNE in aloop with footpoint heating is suppressed unless the background heating is sufficiently small. The implications for thegenerality of TNE are discussed.
  • Journal article
    Cobb A, Czaja A, 2019,

    Mesoscale Signature of the North Atlantic Oscillation and Its Interaction With the Ocean

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 5575-5581, ISSN: 0094-8276
  • Journal article
    Inai Y, Fujita R, Machida T, Matsueda H, Sawa Y, Tsuboi K, Katsumata K, Morimoto S, Aoki S, Nakazawa Tet al., 2019,

    Seasonal characteristics of trace gas transport into the extratropical upper troposphere and lower stratosphere

    , ATMOSPHERIC CHEMISTRY AND PHYSICS, Vol: 19, Pages: 7073-7103, ISSN: 1680-7316
  • Journal article
    Banks JR, Huenerbein A, Heinold B, Brindley HE, Deneke H, Schepanski Ket al., 2019,

    The sensitivity of the colour of dust in MSG-SEVIRI Desert Dust infrared composite imagery to surface and atmospheric conditions

    , Atmospheric Chemistry and Physics, Vol: 19, Pages: 6893-6911, ISSN: 1680-7316

    Infrared “Desert Dust” composite imagery taken by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI), onboard the Meteosat Second Generation (MSG) series of satellites above the equatorial East Atlantic, has been widely used for more than a decade to identify and track the presence of dust storms from and over the Sahara Desert, the Middle East, and southern Africa. Dust is characterised by distinctive pink colours in the Desert Dust false-colour imagery; however, the precise colour is influenced by numerous environmental properties, such as the surface thermal emissivity and skin temperature, the atmospheric water vapour content, the quantity and height of dust in the atmosphere, and the infrared optical properties of the dust itself. For this paper, simulations of SEVIRI infrared measurements and imagery have been performed using a modelling system, which combines dust concentrations simulated by the aerosol transport model COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model) with radiative transfer simulations from the RTTOV (Radiative Transfer for TOVS) model. Investigating the sensitivity of the synthetic infrared imagery to the environmental properties over a 6-month summertime period from 2011 to 2013, it is confirmed that water vapour is a major control on the apparent colour of dust, obscuring its presence when the moisture content is high. Of the three SEVIRI channels used in the imagery (8.7, 10.8, and 12.0 µm), the channel at 10.8 µm has the highest atmospheric transmittance and is therefore the most sensitive to the surface skin temperature. A direct consequence of this sensitivity is that the background desert surface exhibits a strong diurnal cycle in colour, with light blue colours possible during the day and purple hues prevalent at night. In dusty scenes, the clearest pink colours arise from high-altitude dust in dry atmospheres. Elevated dust

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