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Journal articleVasko IY, Kuzichev I, Artemyev A, et al., 2020, , PHYSICS OF PLASMAS, Vol: 27, ISSN: 1070-664X
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- Citations: 25
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Journal articleSimon Wedlund C, Behar E, Nilsson H, et al., 2020, , Astronomy and Astrophysics: a European journal, Vol: 640, Pages: C3-C3, ISSN: 0004-6361
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Journal articleErgun RE, Ahmadi N, Kromyda L, et al., 2020, , ASTROPHYSICAL JOURNAL, Vol: 898, ISSN: 0004-637X
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- Citations: 53
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Journal articleBowen TA, Bale SD, Bonnell JW, et al., 2020, , ASTROPHYSICAL JOURNAL, Vol: 899, ISSN: 0004-637X
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- Citations: 35
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Journal articleWilder FD, Schwartz SJ, Ergun RE, et al., 2020, , GEOPHYSICAL RESEARCH LETTERS, Vol: 47, ISSN: 0094-8276
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- Citations: 5
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Journal articleFujita R, Morimoto S, Maksyutov S, et al., 2020, , JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 125, ISSN: 2169-897X
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- Citations: 32
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Journal articleGibbins G, Haigh JD, 2020,
Entropy production rates of the climate
, Journal of the Atmospheric Sciences, ISSN: 0022-4928There is ongoing interest in the global entropy production rate as a climate diagnostic and predictor, but progress has been limited by ambiguities in its definition; different conceptual boundaries of the climate system give rise to different internal production rates. Three viable options are described, estimated and investigated here, two of which -- the material and the total radiative (here `planetary') entropy production rates -- are well-established and a third which has only recently been considered but appears very promising. This new option is labelled the `transfer' entropy production rate and includes all irreversible processes that transfer heat within the climate, radiative and material, but not those involved in the exchange of radiation with space. Estimates in three model climates put the material rate in the range 27-48 mW/m^2K, the transfer rate 67-76mW/m^2K, and the planetary rate 1279-1312 mW/m^2K. The climate-relevance of each rate is probed by calculating their responses to climate changes in a simple radiative-convective model. An increased greenhouse effect causes a significant increase in the material and transfer entropy production rates but has no direct impact on the planetary rate. When the same surface temperature increase is forced by changing the albedo instead, the material and transfer entropy production rates increase less dramatically and the planetary rate also registers an increase. This is pertinent to solar radiation management as it demonstrates the difficulty of reversing greenhouse gas-mediated climate changes by albedo alterations. It is argued that the transfer perspective has particular significance in the climate system and warrants increased prominence.
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Journal articleAkhavanTafti M, Palmroth M, Slavin JA, et al., 2020, , Journal of Geophysical 91桃色: Space Physics, Vol: 125, Pages: 1-22, ISSN: 2169-9380
The Vlasiator hybrid鈥怴lasov code was developed to investigate global magnetospheric dynamics at ion鈥恔inetic scales. Here, we focus on the role of magnetic reconnection in the formation and evolution of the magnetic islands at the low鈥恖atitude magnetopause, under southward interplanetary magnetic field (IMF) conditions. The simulation results indicate that: 1) the magnetic reconnection ion kinetics, including the Earthward鈥恜ointing Larmor electric field on the magnetospheric鈥恠ide of an X鈥恜oint and anisotropic ion distributions, are well鈥恈aptured by Vlasiator, thus enabling the study of reconnection鈥恉riven magnetic island evolution processes, 2) magnetic islands evolve due to continuous reconnection at adjacent X鈥恜oints, ‘coalescence’ which refers to the merging of neighboring islands to create a larger island, ‘erosion’ during which an island loses magnetic flux due to reconnection, and ‘division’ which involves the splitting of an island into smaller islands, and 3) continuous reconnection at adjacent X鈥恜oints is the dominant source of magnetic flux and plasma to the outer layers of magnetic islands resulting in cross鈥恠ectional growth rates up to +0.3 RE2/min. The simulation results are compared to the Magnetospheric Multiscale (MMS) measurements of a chain of ion鈥恠cale flux transfer events (FTEs) sandwiched between two dominant X鈥恖ines. The MMS measurements similarly reveal: 1) anisotropic ion populations, and 2) normalized reconnection rate ~0.18, in agreement with theory and the Vlasiator predictions. Based on the simulation results and the MMS measurements, it is estimated that the observed ion鈥恠cale FTEs may grow Earth鈥恠ized within ~10 minutes, which is comparable to the average transport time for FTEs formed in the subsolar region to the high鈥恖atitude magnetopause. Future simulations shall revisit reconnection鈥恉riven island evolution processes with improved spatial resolutions.
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Journal articleEggington JWB, Eastwood JP, Mejnertsen L, et al., 2020, , Journal of Geophysical 91桃色: Space Physics, Vol: 125, Pages: 1-17, ISSN: 2169-9380
The Earth’s dipole tilt angle changes both diurnally and seasonally and introduces numerous variabilities in the coupled magnetosphere鈥恑onosphere system. By altering the location and intensity of magnetic reconnection, the dipole tilt influences convection on a global scale. However, due to the nonlinear nature of the system, various other effects like dipole rotation, varying IMF orientation and non鈥恥niform ionospheric conductance can smear tilt effects arising purely from changes in coupling with the solar wind. To elucidate the underlying tilt angle鈥恉ependence, we perform MHD simulations of the steady鈥恠tate magnetosphere鈥恑onosphere system under purely southward IMF conditions for tilt angles from 0°鈥90°. We identify the location of the magnetic separator in each case, and find that an increasing tilt angle shifts the 3鈥怐 X鈥恖ine southward on the magnetopause due to changes in magnetic shear angle. The separator is highly unsteady above 50° tilt angle, characteristic of regular FTE generation on the magnetopause. The reconnection rate drops as the tilt angle becomes large, but remains continuous across the dayside such that the magnetosphere is open even for 90°. These trends map down to the ionosphere, with the polar cap contracting as the tilt angle increases, and region鈥怚 field鈥恆ligned current (FAC) migrating to higher latitudes with changing morphology. The tilt introduces a north鈥恠outh asymmetry in magnetospheric convection, thus driving more FAC in the northern (sunward鈥恌acing) hemisphere for large tilt angles than in the south independent of conductance. These results highlight the strong sensitivity to onset time in the potential impact of a severe space weather event.
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Journal articleHantson S, Kelley DI, Arneth A, et al., 2020, , Geoscientific Model Development, Vol: 13, Pages: 3299-3318, ISSN: 1991-959X
Global fire-vegetation models are widely used to assess impacts of environmental change on fire regimes and the carbon cycle and to infer relationships between climate, land use and fire. However, differences in model structure and parameterizations, in both the vegetation and fire components of these models, could influence overall model performance, and to date there has been limited evaluation of how well different models represent various aspects of fire regimes. The Fire Model Intercomparison Project (FireMIP) is coordinating the evaluation of state-of-the-art global fire models, in order to improve projections of fire characteristics and fire impacts on ecosystems and human societies in the context of global environmental change. Here we perform a systematic evaluation of historical simulations made by nine FireMIP models to quantify their ability to reproduce a range of fire and vegetation benchmarks. The FireMIP models simulate a wide range in global annual total burnt area (39–536 Mha) and global annual fire carbon emission (0.91–4.75 Pg C yr−1) for modern conditions (2002–2012), but most of the range in burnt area is within observational uncertainty (345–468 Mha). Benchmarking scores indicate that seven out of nine FireMIP models are able to represent the spatial pattern in burnt area. The models also reproduce the seasonality in burnt area reasonably well but struggle to simulate fire season length and are largely unable to represent interannual variations in burnt area. However, models that represent cropland fires see improved simulation of fire seasonality in the Northern Hemisphere. The three FireMIP models which explicitly simulate individual fires are able to reproduce the spatial pattern in number of fires, but fire sizes are too small in key regions, and this results in an underestimation of burnt area. The correct representation of spatial and seasonal patterns in vegetation appears
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Journal articleTang T, Shindell D, Zhang Y, et al., 2020, , Atmospheric Chemistry and Physics, Vol: 20, Pages: 8251-8266, ISSN: 1680-7316
Shortwave cloud radiative effects (SWCREs), defined as the difference of the shortwave radiative flux between all-sky and clear-sky conditions at the surface, have been reported to play an important role in influencing the Earth's energy budget and temperature extremes. In this study, we employed a set of global climate models to examine the SWCRE responses to CO2, black carbon (BC) aerosols, and sulfate aerosols in boreal summer over the Northern Hemisphere. We found that CO2 causes positive SWCRE changes over most of the NH, and BC causes similar positive responses over North America, Europe, and eastern China but negative SWCRE over India and tropical Africa. When normalized by effective radiative forcing, the SWCRE from BC is roughly 3–5 times larger than that from CO2. SWCRE change is mainly due to cloud cover changes resulting from changes in relative humidity (RH) and, to a lesser extent, changes in cloud liquid water, circulation, dynamics, and stability. The SWCRE response to sulfate aerosols, however, is negligible compared to that for CO2 and BC because part of the radiation scattered by clouds under all-sky conditions will also be scattered by aerosols under clear-sky conditions. Using a multilinear regression model, it is found that mean daily maximum temperature (Tmax) increases by 0.15 and 0.13 K per watt per square meter (W m−2) increase in local SWCRE under the CO2 and BC experiment, respectively. When domain-averaged, the contribution of SWCRE change to summer mean Tmax changes was 10 %–30 % under CO2 forcing and 30 %–50 % under BC forcing, varying by region, which can have important implications for extreme climatic events and socioeconomic activities.
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Journal articleSaunois M, Stavert AR, Poulter B, et al., 2020, , Earth System Science Data, Vol: 12, Pages: 1561-1623, ISSN: 1866-3508
Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations).For the 2008–2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH4 yr−1 (range 550–594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH4 yr−1 or ∼ 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336–376 Tg CH4 yr−1 or
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Journal articleMilillo, Fujimoto, Murakami, et al., 2020, , Space Science Reviews, Vol: 216, Pages: 1-78, ISSN: 0038-6308
The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury’s environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors.
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Journal articleStawarz JE, Matteini L, Parashar TN, et al., 2020,
<jats:p>Decomposing the electric field (E) into the contributions fromgeneralized Ohm’s law provides key insight into both nonlinear anddissipative dynamics across the full range of scales within a plasma.Using high-resolution, multi-spacecraft measurements of three intervalsin Earth’s magnetosheath from the Magnetospheric Multiscale mission, theinfluence of the magnetohydrodynamic, Hall, electron pressure, andelectron inertia terms from Ohm’s law, as well as the impact of a finiteelectron mass, on the turbulent spectrum are examined observationallyfor the first time. The magnetohydrodynamic, Hall, and electron pressureterms are the dominant contributions to over the accessible lengthscales, which extend to scales smaller than the electron inertial lengthat the greatest extent, with the Hall and electron pressure termsdominating at sub-ion scales. The strength of the non-ideal electronpressure contribution is stronger than expected from linear kineticAlfvén waves and a partial anti-alignment with the Hall electric fieldis present, linked to the relative importance of electron diamagneticcurrents in the turbulence. The relative contribution of linear andnonlinear electric fields scale with the turbulent fluctuationamplitude, with nonlinear contributions playing the dominant role inshaping for the intervals examined in this study. Overall, the sum ofthe Ohm’s law terms and measured agree to within ~20%across the observable scales. These results both confirm generalexpectations about the behavior of in turbulent plasmas and highlightfeatures that should be explored further theoretically.</jats:p>
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Journal articleBowen TA, Mallet A, Bale SD, et al., 2020, , PHYSICAL REVIEW LETTERS, Vol: 125, ISSN: 0031-9007
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- Citations: 46
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Journal articleMartin CJ, Ray LC, Constable DA, et al., 2020, , Journal of Geophysical 91桃色: Space Physics, Vol: 125, ISSN: 2169-9380
Ionospheric outflow is the flow of plasma initiated by a loss of equilibrium along a magnetic field line which induces an ambipolar electric field due to the separation of electrons and ions in a gravitational field and other mass dependant sources. We have developed an ionospheric outflow model using the transport equations to determine the number of particles that flow into the outer magnetosphere of Jupiter. The model ranges from 1400 km in altitude above the 1 bar level to 2.5 RJ along the magnetic field line and considers H+ and H3+ as the main ion constituents. Previously, only pressure gradients and gravitational forces were considered in modelling polar wind. However, at Jupiter we need to evaluate the affect of field鈥恆ligned currents present in the auroral regions due to the breakdown of corotation in the magnetosphere, along with the centrifugal force exerted on the particles due to the fast planetary rotation rate. The total number flux from both hemispheres is found to be 1.3鈥1.8 x 1028 s鈥1 comparable in total number flux to the Io plasma source. The mass flux is lower due to the difference in ion species. This influx of protons from the ionosphere into the inner and middle magnetosphere needs to be included in future assessments of global flux tube dynamics and composition of the magnetosphere system.
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Journal articleCao H, Dougherty MK, Hunt GJ, et al., 2020, , ICARUS, Vol: 344, ISSN: 0019-1035
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- Citations: 41
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Journal articleDiaz-Aguado MF, Bonnell JW, Bale SD, et al., 2020, , JOURNAL OF SPACECRAFT AND ROCKETS, Vol: 57, Pages: 793-808, ISSN: 0022-4650
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- Citations: 1
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Journal articleHuang SY, Zhang J, Sahraoui F, et al., 2020, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 897, ISSN: 2041-8205
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- Citations: 40
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Journal articleStarkey M, Fuselier SA, Desai MI, et al., 2020, , ASTROPHYSICAL JOURNAL, Vol: 897, ISSN: 0004-637X
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- Citations: 2
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Journal articleOliveros JCM, Diaz Castillo SM, Krupar V, et al., 2020, , ASTROPHYSICAL JOURNAL, Vol: 897, ISSN: 0004-637X
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- Citations: 1
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Journal articleMagurno D, Cossich W, Maestri T, et al., 2020, , Remote Sensing, Vol: 12, Pages: 1-19, ISSN: 2072-4292
Airborne interferometric data, obtained from the Cirrus Coupled Cloud-Radiation Experiment (CIRCCREX) and from the PiknMix-F field campaign, are used to test the ability of a machine learning cloud identification and classification algorithm (CIC). Data comprise a set of spectral radiances measured by the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) and the Airborne 91桃色 Interferometer Evaluation System (ARIES). Co-located measurements of the two sensors allow observations of the upwelling radiance for clear and cloudy conditions across the far- and mid-infrared part of the spectrum. Theoretical sensitivity studies show that the performance of the CIC algorithm improves with cloud altitude. These tests also suggest that, for conditions encompassing those sampled by the flight campaigns, the additional information contained within the far-infrared improves the algorithm’s performance compared to using mid-infrared data only. When the CIC is applied to the airborne radiance measurements, the classification performance of the algorithm is very high. However, in this case, the limited temporal and spatial variability in the measured spectra results in a less obvious advantage being apparent when using both mid- and far-infrared radiances compared to using mid-infrared information only. These results suggest that the CIC algorithm will be a useful addition to existing cloud classification tools but that further analyses of nadir radiance observations spanning the infrared and sampling a wider range of atmospheric and cloud conditions are required to fully probe its capabilities. This will be realised with the launch of the Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission, ESA’s 9th Earth Explorer.
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Journal articleKollmann, Cohen, Allen, et al., 2020, , Space Science Reviews, Vol: 216, ISSN: 0038-6308
Uranus and Neptune are the least-explored planets in our Solar System. This paper summarizesmysteries about these incredibly intriguing planets and their environments spurred by our limitedobservations from Voyager 2 and Earth-based systems. Several of these observations are eitherinconsistent with our current understanding built from exploring other planetary systems, orindicate such unique characteristics of these Ice Giants that they leave us with more questions thananswers. This paper specifically focuses on the value of all aspects of magnetosphericmeasurements, from the radiation belt structure to plasma dynamics to coupling to the solar wind,through a future mission to either of these planets. Such measurements have large interdisciplinaryvalue, as demonstrated by the large number of mysteries discussed in this paper that cover othernon-magnetospheric disciplines, including planetary interiors, atmospheres, rings, and moons.
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Journal articleArcher MO, 2020, , Geoscience Communication, Vol: 3, Pages: 147-166, ISSN: 2569-7110
The ultra-low frequency analogues of sound waves in Earth'smagnetosphere play a crucial role in space weather; however, the publicis largely unaware of this risk to our everyday lives and technology.As a way of potentially reaching new audiences, SSFX (Space Sound Effects) made 8 yearsof satellite wave recordings audible to the human ear with the aimof using it to create art. Partnering with film industry professionals,the standard processes of international film festivals were adoptedby the project in order to challenge independent filmmakers to incorporatethese sounds into short films in creative ways. Seven films coveringa wide array of topics and genres (despite coming from the same sounds)were selected for screening at a special film festival out of 22 submissions.The works have subsequently been shown at numerous established filmfestivals and screenings internationally. These events have attracteddiverse non-science audiences resulting in several unanticipated impacts on them, thereby demonstrating how working with the art world canopen up dialogues with both artists and audiences who would not ordinarily engage with science.
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Journal articleWang S, Rashid T, Thorp H, et al., 2020, , Geophysical 91桃色 Letters, Vol: 47, Pages: 28 Jul 2020-28 Jul 2020, ISSN: 0094-8276
In this study a comprehensive picture of the changing intensity life cycle of major (Category 3 and higher) tropical cyclones (TCs) is presented. Over the past decades, the lifetime maximum intensity has increased, but there has also been a significant decrease in duration of time spent at intensities greater than Category 1. These compensating effects have maintained a stable global mean鈥恆ccumulated cyclone energy of individual major TCs. The global mean duration of major TCs has shortened by about 1 day from 1982 to 2018. There has been both faster intensification (Categories 1 to 3) and weakening (Categories 3 to 1) by about 40%. The probabilities of rapid intensification and rapid weakening have both risen in the period 2000–2018 compared to 1982–1999. A statistically significant anticorrelation is found between the lifetime maximum intensity and the following duration of the final weakening. This suggests an element of self鈥恟egulation of TC life cycles.
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Journal articleMadanian H, Schwartz SJ, Halekas JS, et al., 2020, , GEOPHYSICAL RESEARCH LETTERS, Vol: 47, ISSN: 0094-8276
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- Citations: 6
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Journal articleVasko IY, Wang R, Mozer FS, et al., 2020, , FRONTIERS IN PHYSICS, Vol: 8, ISSN: 2296-424X
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- Citations: 36
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Journal articleBandyopadhyay R, Sorriso-Valvo L, Chasapis A, et al., 2020, , Physical Review Letters, Vol: 124, Pages: 225101 鈥 1-225101 鈥 7, ISSN: 0031-9007
We present estimates of the turbulent energy-cascade rate derived from a Hall-magnetohydrodynamic (MHD) third-order law. We compute the contribution from the Hall term and the MHD term to the energy flux. Magnetospheric Multiscale (MMS) data accumulated in the magnetosheath and the solar wind are compared with previously established simulation results. Consistent with the simulations, we find that at large (MHD) scales, the MMS observations exhibit a clear inertial range dominated by the MHD flux. In the subion range, the cascade continues at a diminished level via the Hall term, and the change becomes more pronounced as the plasma beta increases. Additionally, the MHD contribution to interscale energy transfer remains important at smaller scales than previously thought. Possible reasons are offered for this unanticipated result.
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Journal articleYang L, Wang L, Zhao L, et al., 2020, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 896, ISSN: 2041-8205
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- Citations: 4
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Journal articleCarnielli G, Galand M, Leblanc F, et al., 2020, , Icarus, Vol: 343, Pages: 1-11, ISSN: 0019-1035
Ganymede's neutral and plasma environments are poorly constrained by observations. Carnielli et al. (2019) developed the first 3D ionospheric model aimed at understanding the dynamics of the present ion species and at quantifying the presence of each component in the moon's magnetosphere. The model outputs were compared with Galileo measurements of the ion energy flux, ion bulk velocity and electron number density made during the G2 flyby. A good agreement was found in terms of ion energy distribution and bulk velocity, but not in terms of electron number density. In this work, we present some improvements to our model Carnielli et al. (2019) and quantitatively address the possible sources of the discrepancy found in the electron number density between the Galileo observations and our ionospheric model. We have improved the ion model by developing a collision scheme to simulate the charge-exchange interaction between the exosphere and the ionosphere. We have simulated the energetic component of the O$_2$ population, which is missing in the exospheric model of Leblanc et al. (2017) and added it to the original distribution, hence improving its description at high altitudes. These improvements are found to be insufficient to explain the discrepancy in the electron number density. We provide arguments that the input O$_2$ exosphere is underestimated and that the plasma production acts asymmetrically between the Jovian and anti-Jovian hemispheres. In particular, we estimate that the O$_2$ column density should be greater than $10^{15}$~cm$^{-2}$, i.e., higher than previously derived upper limits (and a factor 10 higher than the values from Leblanc et al. (2017)), and that the ionization frequency from electron impact must be higher in the anti-Jovian hemisphere for the G2 flyby conditions.
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