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Journal articleØieroset M, Phan TD, Drake JF, et al., 2019,
Reconnection with magnetic flux pileup at the interface of converging jets at the magnetopause
, Geophysical Research Letters, Vol: 46, Pages: 1937-1946, ISSN: 0094-8276We report Magnetospheric Multiscale observations of reconnection in a thin current sheet at the interface of interlinked flux tubes carried by converging reconnection jets at Earth's magnetopause. The ion skin depth‐scale width of the interface current sheet and the non‐frozen‐in ions indicate that Magnetospheric Multiscale crossed the reconnection layer near the X‐line, through the ion diffusion region. Significant pileup of the reconnecting component of the magnetic field in this and three other events on approach to the interface current sheet was accompanied by an increase in magnetic shear and decrease in Δβ, leading to conditions favorable for reconnection at the interface current sheet. The pileup also led to enhanced available magnetic energy per particle and strong electron heating. The observations shed light on the evolution and energy release in 3‐D systems with multiple reconnection sites.
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Journal articleDimmock AP, Russell CT, Sagdeev RZ, et al., 2019,
Direct evidence of nonstationary collisionless shocks in space plasmas
, Science Advances, Vol: 5, ISSN: 2375-2548Collisionless shocks are ubiquitous throughout the universe: around stars, supernova remnants, active galactic nuclei, binary systems, comets, and planets. Key information is carried by electromagnetic emissions from particles accelerated by high Mach number collisionless shocks. These shocks are intrinsically nonstationary, and the characteristic physical scales responsible for particle acceleration remain unknown. Quantifying these scales is crucial, as it affects the fundamental process of redistributing upstream plasma kinetic energy into other degrees of freedom-particularly electron thermalization. Direct in situ measurements of nonstationary shock dynamics have not been reported. Thus, the model that best describes this process has remained unknown. Here, we present direct evidence demonstrating that the transition to nonstationarity is associated with electron-scale field structures inside the shock ramp.
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Journal articleDubois D, Carrasco N, Bourgalais J, et al., 2019,
Nitrogen-containing Anions and Tholin Growth in Titan's Ionosphere: Implications for Cassini CAPS-ELS Observations
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 872, ISSN: 2041-8205 -
Journal articleProvan G, Cowley SWH, Bunce EJ, et al., 2019,
Variability of Intra-D Ring Azimuthal Magnetic Field Profiles Observed on Cassini's Proximal Periapsis Passes
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 379-404, ISSN: 2169-9380 -
Journal articleGingell I, Schwartz SJ, Eastwood JP, et al., 2019,
Observations of magnetic reconnection in the ransition region of quasi-parallel hocks
, Geophysical Research Letters, Vol: 46, Pages: 1177-1184, ISSN: 0094-8276Using observations of Earth's bow shock by the Magnetospheric Multiscale mission, we show for the first time that active magnetic reconnection is occurring at current sheets embedded within the quasi‐parallel shock's transition layer. We observe an electron jet and heating but no ion response, suggesting we have observed an electron‐only mode. The lack of ion response is consistent with simulations showing reconnection onset on sub‐ion time scales. We also discuss the impact of electron heating in shocks via reconnection.
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Journal articleBall WT, Rozanov EV, Alsing J, et al., 2019,
The upper stratospheric solar cycle ozone response
, Geophysical Research Letters, Vol: 46, Pages: 1831-1841, ISSN: 0094-8276The solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1–10 hPa) zonally averaged spatial responses; this and the recommended data set for comparison remains disputed. Recent data-merging advancements have led to more robust observational data. Using these data, we show that the observed SC signal exhibits an upper stratosphere U-shaped spatial structure with lobes emanating from the tropics (5–10 hPa) to high altitudes at midlatitudes (1–3 hPa). We confirm this using two independent chemistry climate models in specified dynamics mode and an idealized timeslice experiment. We recommend the BASIC v2 ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used.
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Journal articleArcher MO, Hietala H, Hartinger MD, et al., 2019,
Direct observations of a surface eigenmode of the dayside magnetopause
, Nature Communications, Vol: 10, ISSN: 2041-1723The abrupt boundary between a magnetosphere and the surrounding plasma, the magnetopause, has long been known to support surface waves. It was proposed that impulses acting on the boundary might lead to a trapping of these waves on the dayside by the ionosphere, resulting in a standing wave or eigenmode of the magnetopause surface. No direct observational evidence of this has been found to date and searches for indirect evidence have proved inconclusive, leading to speculation that this mechanism might not occur. By using fortuitous multipoint spacecraft observations during a rare isolated fast plasma jet impinging on the boundary, here we show that the resulting magnetopause motion and magnetospheric ultra-low frequency waves at well-defined frequencies are in agreement with and can only be explained by the magnetopause surface eigenmode. We therefore show through direct observations that this mechanism, which should impact upon the magnetospheric system globally, does in fact occur.
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Journal articleFerri F, Karatekin O, Lewis SR, et al., 2019,
ExoMars Atmospheric Mars Entry and Landing Investigations and Analysis (AMELIA)
, SPACE SCIENCE REVIEWS, Vol: 215, ISSN: 0038-6308 -
Journal articleVasko IY, Krasnoselskikh V, Tong Y, et al., 2019,
Whistler Fan Instability Driven by Strahl Electrons in the Solar Wind
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 871, ISSN: 2041-8205- Author Web Link
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- Citations: 57
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Journal articleNakamura R, Genestreti KJ, Nakamura T, et al., 2019,
Structure of the current sheet in the 11 July 2017 Electron Diffusion Region Event
, Journal of Geophysical Research: Space Physics, Vol: 124, Pages: 1173-1186, ISSN: 2169-9380The structure of the current sheet along the Magnetospheric Multiscale (MMS) orbit is examined during the 11 July 2017 Electron Diffusion Region (EDR) event. The location of MMS relative to the X‐line is deduced and used to obtain the spatial changes in the electron parameters. The electron velocity gradient values are used to estimate the reconnection electric field sustained by nongyrotropic pressure. It is shown that the observations are consistent with theoretical expectations for an inner EDR in 2‐D reconnection. That is, the magnetic field gradient scale, where the electric field due to electron nongyrotropic pressure dominates, is comparable to the gyroscale of the thermal electrons at the edge of the inner EDR. Our approximation of the MMS observations using a steady state, quasi‐2‐D, tailward retreating X‐line was valid only for about 1.4 s. This suggests that the inner EDR is localized; that is, electron outflow jet braking takes place within an ion inertia scale from the X‐line. The existence of multiple events or current sheet processes outside the EDR may play an important role in the geometry of reconnection in the near‐Earth magnetotail.
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Journal articleTurner DL, Kilpua EKJ, Hietala H, et al., 2019,
The Response of Earth's Electron Radiation Belts to Geomagnetic Storms: Statistics From the Van Allen Probes Era Including Effects From Different Storm Drivers
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 1013-1034, ISSN: 2169-9380 -
Journal articleAngelopoulos V, Cruce P, Drozdov A, et al., 2019,
The Space Physics Environment Data Analysis System (SPEDAS)
, SPACE SCIENCE REVIEWS, Vol: 215, ISSN: 0038-6308- Author Web Link
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- Citations: 290
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Journal articleJanvier M, Winslow RM, Good S, et al., 2019,
Generic Magnetic Field Intensity Profiles of Interplanetary Coronal Mass Ejections at Mercury, Venus, and Earth From Superposed Epoch Analyses
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 812-836, ISSN: 2169-9380- Author Web Link
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- Citations: 58
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Journal articleEastwood J, Hapgood MA, Biffis E, et al., 2019,
Quantifying the economic value of space weather forecasting for power grids: An exploratory study
, Space Weather, Vol: 16, Pages: 2052-2067, ISSN: 1539-4956An accurate understanding of space weather socioeconomic impact is fundamental to the development of appropriate operational services, forecasting capabilities, and mitigation strategies. One way to approach this problem is by developing physics‐based models and frameworks that can lead to a bottom‐up estimate of risk and likely impact. Here we describe the development of a new framework to assess the economic impact of space weather on power distribution networks and the supply of electricity. In particular, we focus on the phenomenon of the geomagnetic substorm, which is relatively localized in time and space, and occurs multiple times with varying severity during a geomagnetic storm. The framework uses the AE index to characterize substorm severity, and the impact of the substorm is modulated by the resilience of the power grid and the nature of available forecast. Possible scenarios for substorm sequences during a 1‐in‐10‐, a 1‐in‐30‐, and a 1‐in‐100‐year geomagnetic storm events are generated based on the 2003, 1989, and 1859 geomagnetic storms. Economic impact, including international spill over, can then be calculated using standard techniques, based on the duration and the geographical footprint of the power outage. Illustrative calculations are made for the European sector, for a variety of forecast and resilience scenarios. However, currently available data are highly regionally inhomogeneous, frustrating attempts to define an overall global economic impact at the present time.
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Journal articleStansby D, Horbury T, Matteini L, 2019,
Diagnosing solar wind origins using in situ measurements in the inner heliosphere
, Monthly Notices of the Royal Astronomical Society, Vol: 482, Pages: 1706-1714, ISSN: 0035-8711Robustly identifying the solar sources of individual packets of solar wind measured in interplanetary space remains an open problem. We set out to see if this problem is easier to tackle using solar wind measurements closer to the Sun than 1 au, where the mixing and dynamical interaction of different solar wind streams is reduced. Using measurements from the Helios mission, we examined how the proton core temperature anisotropy and cross-helicity varied with distance. At 0.3 au there are two clearly separated anisotropic and isotropic populations of solar wind that are not distinguishable at 1 au. The anisotropic population is always Alfvénic and spans a wide range of speeds. In contrast the isotropic population has slow speeds, and contains a mix of Alfvénic wind with constant mass fluxes and non-Alfvénic wind with large and highly varying mass fluxes. We split the in situ measurements into three categories according these observations, and suggest that these categories correspond to wind that originated in the core of coronal holes, in or near active regions or the edges of coronal holes, and as small transients form streamers or pseudo-streamers. Although our method by itself is simplistic, it provides a new tool that can be used in combination with other methods for identifying the sources of solar wind measured by Parker Solar Probe and Solar Orbiter.
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Conference paperNowack P, Ong QYE, Braesicke P, et al., 2019,
Machine learning parameterizations for ozone in climate sensitivity simulations
, Kurzfassungen der Meteorologentagung DACH -
Journal articleMalik A, Nowack PJ, Haigh JD, et al., 2019,
Tropical Pacific Climate Variability under Solar Geoengineering: Impacts on ENSO Extremes
<jats:p>Abstract. Many modelling studies suggest that the El Niño Southern Oscillation (ENSO), in interaction with the tropical Pacific background climate, will change under rising atmospheric greenhouse gas concentrations. Solar geoengineering (reducing the solar flux from outer space) has been proposed as a means to counteract anthropogenic greenhouse-induced changes in climate. Effectiveness of solar geoengineering is uncertain. Robust results are particularly difficult to obtain for ENSO because existing geoengineering simulations are too short (typically ~ 50 years) to detect statistically significant changes in the highly variable tropical Pacific background climate. We here present results from a 1000-year sunshade geoengineering simulation, G1, carried out with the coupled atmosphere-ocean general circulation model HadCM3L. In agreement with previous studies, reducing the shortwave solar flux more than compensates the warming in the tropical Pacific that develops in the 4×CO2 scenario: we observe an overcooling of 0.3 °C (5 %) and 0.23-mm day−1 (5 %) reduction in mean rainfall relative to preindustrial conditions in the G1 simulation. This is due to the different latitudinal distributions of the shortwave (solar) and longwave (CO2) forcings.The location of the Intertropical Convergence Zone (ITCZ) located north of equator in the tropical Pacific, which moved 7.5° southwards under 4×CO2, is also restored to its preindustrial location. However, other aspects of the tropical Pacific mean climate are not reset as effectively. Relative to preindustrial conditions, in G1 the zonal wind stress, zonal sea surface temperature (SST) gradient, and meridional SST gradient are reduced by 10 %, 11 %, and 9 %, respectively, and the Pacific Walker Circulation (PWC) is consistently weakened. The overall amplitude of ENSO strengthens by 5–8 %, but there is a 65 % reduct
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Journal articleMalik A, Nowack PJ, Haigh JD, et al., 2019,
Supplementary material to &quot;Tropical Pacific Climate Variability under Solar Geoengineering: Impacts on ENSO Extremes&quot;
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Journal articleDiaz-Aguado MF, Bonnell JW, Bale SD, et al., 2019,
Experimental Investigation of Total Photoemission Yield from New Satellite Surface Materials
, JOURNAL OF SPACECRAFT AND ROCKETS, Vol: 56, Pages: 248-258, ISSN: 0022-4650- Author Web Link
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- Citations: 7
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Journal articlePapini E, Franci L, Landi S, et al., 2019,
Can Hall Magnetohydrodynamics Explain Plasma Turbulence at Sub-ion Scales?
, ASTROPHYSICAL JOURNAL, Vol: 870, ISSN: 0004-637X -
Journal articlePapini E, Franci L, Landi S, et al., 2019,
Statistics of magnetic reconnection and turbulence in Hall-MHD and hybrid-PIC simulations
, NUOVO CIMENTO C-COLLOQUIA AND COMMUNICATIONS IN PHYSICS, Vol: 42, ISSN: 2037-4909 -
Journal articleLandi S, Franci L, Papini E, et al., 2019,
Spectral anisotropies in high resolution three-dimensional simulations
, NUOVO CIMENTO C-COLLOQUIA AND COMMUNICATIONS IN PHYSICS, Vol: 42, ISSN: 2037-4909 -
Journal articleVerdini A, Grappin R, Montagud-Camps V, et al., 2019,
Numerical simulations of high cross-helicity turbulence from 0.2 to 1 AU
, NUOVO CIMENTO C-COLLOQUIA AND COMMUNICATIONS IN PHYSICS, Vol: 42, ISSN: 2037-4909 -
Journal articleTong Y, Vasko IY, Pulupa M, et al., 2019,
Whistler Wave Generation by Halo Electrons in the Solar Wind
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 870, ISSN: 2041-8205- Author Web Link
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- Citations: 50
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Journal articleThompson DWJ, Ceppi P, Li Y, 2019,
A robust constraint on the temperature and height of the extratropical tropopause
, Journal of Climate, Vol: 32, Pages: 273-287, ISSN: 0894-8755In a recent study, the authors hypothesize that the Clausius–Clapeyron relation provides a strong constraint on the temperature of the extratropical tropopause and hence the depth of mixing by extratropical eddies. The hypothesis is a generalization of the fixed-anvil temperature hypothesis to the global atmospheric circulation. It posits that the depth of robust mixing by extratropical eddies is limited by radiative cooling by water vapor—and hence saturation vapor pressures—in areas of sinking motion. The hypothesis implies that 1) radiative cooling by water vapor constrains the vertical structure and amplitude of extratropical dynamics and 2) the extratropical tropopause should remain at roughly the same temperature and lift under global warming. Here the authors test the hypothesis in numerical simulations run on an aquaplanet general circulation model (GCM) and a coupled atmosphere–ocean GCM (AOGCM). The extratropical cloud-top height, wave driving, and lapse-rate tropopause all shift upward but remain at roughly the same temperature when the aquaplanet GCM is forced by uniform surface warming of +4 K and when the AOGCM is forced by RCP8.5 scenario emissions. “Locking” simulations run on the aquaplanet GCM further reveal that 1) holding the water vapor concentrations input into the radiation code fixed while increasing surface temperatures strongly constrains the rise in the extratropical tropopause, whereas 2) increasing the water vapor concentrations input into the radiation code while holding surface temperatures fixed leads to robust rises in the extratropical tropopause. Together, the results suggest that roughly invariant extratropical tropopause temperatures constitutes an additional “robust response” of the climate system to global warming.
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Journal articleTrotta D, Burgess D, 2019,
Electron acceleration at quasi-perpendicular shocks in sub- and supercritical regimes: 2D and 3D simulations
, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 482, Pages: 1154-1162, ISSN: 0035-8711- Author Web Link
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- Citations: 27
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Conference paperPudney M, King S, Horbury T, et al., 2019,
SOLAR ORBITER STRATEGIES FOR EMC CONTROL AND VERIFICATION
, ESA Workshop on Aerospace EMC (Aerospace EMC), Publisher: IEEE- Author Web Link
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- Citations: 7
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Book chapterDougherty M, Christensen U, Cao H, et al., 2019,
Saturn's Magnetic Field and Dynamo
, Saturn in the 21st Century, Editors: Baines, Flasar, Krupp, Stallard, Publisher: Cambridge University Press, Pages: 69-96, ISBN: 978-1-107-10677-2 -
Conference paperBrown P, Auster U, Bergman JES, et al., 2019,
MEETING THE MAGNETIC EMC CHALLENGES FOR THE IN-SITU FIELD MEASUREMENTS ON THE JUICE MISSION
, ESA Workshop on Aerospace EMC (Aerospace EMC), Publisher: IEEE- Author Web Link
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- Citations: 5
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Journal articleTorbert RB, Burch JL, Phan TD, et al., 2018,
Electron-scale dynamics of the diffusion region during symmetric magnetic reconnection in space.
, Science, Vol: 362, Pages: 1391-1395Magnetic reconnection is an energy conversion process that occurs in many astrophysical contexts including Earth's magnetosphere, where the process can be investigated in situ by spacecraft. On 11 July 2017, the four Magnetospheric Multiscale spacecraft encountered a reconnection site in Earth's magnetotail, where reconnection involves symmetric inflow conditions. The electron-scale plasma measurements revealed (i) super-Alfvénic electron jets reaching 15,000 kilometers per second; (ii) electron meandering motion and acceleration by the electric field, producing multiple crescent-shaped structures in the velocity distributions; and (iii) the spatial dimensions of the electron diffusion region with an aspect ratio of 0.1 to 0.2, consistent with fast reconnection. The well-structured multiple layers of electron populations indicate that the dominant electron dynamics are mostly laminar, despite the presence of turbulence near the reconnection site.
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