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Journal articleStaniland NR, Dougherty MK, Masters A, et al., 2021,
The cushion region and dayside magnetodisc structure at Saturn
, Geophysical Research Letters, Vol: 48, Pages: 1-9, ISSN: 0094-8276A sustained quasi‐dipolar magnetic field between the current sheet outer edge and the magnetopause, known as a cushion region, has previously been observed at Jupiter, but not yet at Saturn. Using the complete Cassini magnetometer data, the first evidence of a cushion region forming at Saturn is shown. Only five examples of a sustained cushion are found, revealing this phenomenon to be rare. Four of the cushion regions are identified at dusk and one pre‐noon. It is suggested that greater heating of plasma post‐noon coupled with the expansion of the field through the afternoon sector makes the disc more unstable in this region. These results highlight a key difference between the Saturn and Jupiter systems.
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Journal articleStephenson P, Galand M, Feldman PD, et al., 2021,
Multi-instrument analysis of far-ultraviolet aurora in the southern hemisphere of Comet 67P/Churyumov-Gerasimenko
, Astronomy and Astrophysics: a European journal, Vol: 647, Pages: 1-19, ISSN: 0004-6361Aims. We aim to determine whether dissociative excitation of cometary neutrals by electron impact is the major source of far ultraviolet (FUV) emissions at comet 67P/Churyumov-Gerasimenko in the southern hemisphere at large heliocentric distances, bothduring quiet conditions and impacts of corotating interaction regions observed in the summer of 2016.Methods. We combined multiple datasets from the Rosetta mission through a multi-instrument analysis to complete the first forwardmodelling of FUV emissions in the southern hemisphere of comet 67P and compared modelled brightnesses to observations with theAlice FUV imaging spectrograph. We modelled the brightness of OI1356, OI1304, Lyman-β, CI1657, and CII1335 emissions, whichare associated with the dissociation products of the four major neutral species in the coma: CO2, H2O, CO, and O2. The suprathermalelectron population was probed by the Ion and Electron Sensor of the Rosetta Plasma Consortium (RPC/IES) and the neutral col umn density was constrained by several instruments: the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), theMicrowave Instrument for the Rosetta Orbiter (MIRO) and the Visual InfraRed Thermal Imaging Spectrometer (VIRTIS).Results. The modelled and observed brightnesses of the FUV emission lines agree closely when viewing nadir and dissociativeexcitation by electron impact is shown to be the dominant source of emissions away from perihelion. The CII1335 emissions areshown to be consistent with the volume mixing ratio of CO derived from ROSINA. When viewing the limb during the impactsof corotating interaction regions, the model reproduces brightnesses of OI1356 and CI1657 well, but resonance scattering in theextended coma may contribute significantly to the observed Lyman-β and OI1304 emissions. The correlation between variationsin the suprathermal electron flux and the observed FUV line brightnesses when viewing the comet’s limb suggests electrons areaccelerated on
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Journal articleGoodrich KA, Bonnell JW, Curry S, et al., 2021,
Evidence of Subproton-Scale Magnetic Holes in the Venusian Magnetosheath
, GEOPHYSICAL RESEARCH LETTERS, Vol: 48, ISSN: 0094-8276- Author Web Link
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- Citations: 19
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Journal articleSiddle AG, Mueller-Wodarg ICF, Bruinsma S, et al., 2021,
Density structures in the martian lower thermosphere as inferred by Trace Gas Orbiter accelerometer measurements
, ICARUS, Vol: 357, ISSN: 0019-1035- Author Web Link
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- Citations: 5
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Journal articleSchwartz SJ, Ergun RE, Harald K, et al., 2021,
Evaluating the de Hoffmann-Teller cross-shock potential at real collisionless shocks
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Journal articleNave G, Clear C, 2021,
Reference wavelengths of Si ii, C ii, Fe i, and Ni ii for quasar absorption spectroscopy
, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 502, Pages: 5679-5685, ISSN: 0035-8711 -
Conference paperVuorinen L, Vainio R, Hietala H, et al., 2021,
Jet-driven bow waves as electron accelerators in the magnetosheath: Monte Carlo simulations
<jats:p>&lt;p&gt;Magnetosheath jets are fast flows of plasma frequently observed downstream of the Earth's quasi-parallel shock. Previous observations have shown that these jets can exhibit supermagnetosonic speeds relative to the background flow and develop their own bow waves or shocks. Such jets have been observed to be able to accelerate ions and electrons. In our study, we model electron acceleration by jet-driven bow waves in the magnetosheath using test-particle Monte Carlo simulations that include magnetic mirroring and pitch-angle scattering of magnetic irregularities. We compare the simulation results to spacecraft observations of similar events to understand the acceleration mechanisms at play. Our preliminary results suggest that the energy increase of electrons can be explained by shock drift acceleration at the moving bow wave. Our simulations allow us to estimate the efficiency of acceleration as a function of different jet and magnetosheath parameters. The acceleration introduced by jet-driven bow waves amplifies shock acceleration downstream of the Earth&amp;#8217;s bow shock and may also be applicable to other shock environments.&lt;/p&gt;</jats:p>
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Journal articleTrotta D, Valentini F, Burgess D, et al., 2021,
Particle energisation and transport at collisionless shocks propagating through turbulent media.
<jats:p>&lt;p&gt;Shocks and turbulence are spectacular, ubiquitous phenomena and are crucial ingredients to understand the production and transport of energetic particles in several astrophysical systems. The interaction between an oblique, supercritical shock and fully developed plasma turbulence is here investigated by means of kinetic simulations, for different turbulence amplitudes. The role of pre-existing, upstream turbulence on plasma transport is addressed using a novel technique, relying on the coarse-graining of the Vlasov equation. We find that the upstream transport properties strongly depend on upstream turbulence strength, with patterns modulated by the presence of turbulent structures. These results are relevant for a variety of systems, ranging from the Earth's bow shock interacting with solar wind turbulence, to the largest scales of radio relics in galaxy clusters.&lt;/p&gt;</jats:p>
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Journal articleMansfield L, Nowack P, Voulgarakis A, 2021,
Predicting climate model response to changing emissions
<jats:p>&lt;p&gt;In order to make predictions on how the climate would respond to changes in global and regional emissions, we typically run simulations on Global Climate Models (GCMs) with perturbed emissions or concentration fields. These simulations are highly expensive and often require the availability of high-performance computers. Machine Learning (ML) can provide an alternative approach to estimating climate response to various emissions quickly and cheaply.&amp;#160;&lt;/p&gt;&lt;p&gt;We will present a Gaussian process emulator capable of predicting the global map of temperature response to different types of emissions (both greenhouse gases and aerosol pollutants), trained on a carefully designed set of simulations from a GCM. This particular work involves making short-term predictions on 5 year timescales but can be linked to an emulator from previous work that predicts on decadal timescales. We can also examine uncertainties associated with predictions to find out where where the method could benefit from increased training data. This is a particularly useful asset when constructing emulators for complex models, such as GCMs, where obtaining training runs is costly.&amp;#160;&lt;/p&gt;</jats:p>
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Journal articleWells C, Voulgarakis A, 2021,
The local and remote atmospheric impacts of Africa&#8217;s 21st century aerosol emission trajectory
<jats:p>&lt;p&gt;Aerosols are a major climate forcer, but their historical effect has the largest uncertainty of any forcing; their mechanisms and impacts are not well understood. Due to their short lifetime, aerosols have large impacts near their emission region, but they also have effects on the climate in remote locations. In recent years, studies have investigated the influences of regional aerosols on global and regional climate, and the mechanisms that lead to remote responses to their inhomogeneous forcing. Using the Shared Socioeconomic Pathway scenarios (SSPs), transient future experiments were performed in UKESM1, testing the effect of African emissions following the SSP3-RCP7.0 scenario as the rest of the world follows SSP1-RCP1.9, relative to a global SSP1-RCP1.9 control. SSP3 sees higher direct anthropogenic aerosol emissions, but lower biomass burning emissions, over Africa. Experiments were performed changing each of these sets of emissions, and both. A further set of experiments additionally accounted for changing future CO&lt;sub&gt;2&lt;/sub&gt; concentrations, to investigate the impact of CO&lt;sub&gt;2&lt;/sub&gt; on the responses to aerosol perturbations. Impacts on radiation fluxes, temperature, circulation and precipitation are investigated, both over the emission region (Africa), where microphysical effects dominate, and remotely, where dynamical influences become more relevant.&amp;#160;&lt;/p&gt;</jats:p>
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Journal articleMillington J, Perkins O, Kasoar M, et al., 2021,
Advancing representation of anthropogenic fire in dynamic global vegetation models
<jats:p>&lt;div&gt;&lt;p&gt;It is now commonly-understood that improved understanding of global fire regimes demands better representation of anthropogenic fire in dynamic global vegetation models (DGVMs). However, currently there is no clear agreement on how human activity should be incorporated into fire-enabled DGVMs and existing models exhibit large differences in the sensitivities of socio-economic variables. Furthermore, existing approaches are limited to empirical statistical relations between fire regime variables and globally available socio-economic indicators such as population density or GDP. Although there has been some limited representation in global models of the contrasting ways in which different classes of actors use or manage fires, we argue that fruitful progress in advancing representation of anthropogenic fire in DGVMs will come by building on agent-based modelling approaches. Here, we report on our progress developing a global agent-based representation of anthropogenic fire and its coupling with the JULES-INFERNO fire-enabled DGVM.&amp;#160;&amp;#160;&lt;/p&gt;&lt;/div&gt;&lt;div&gt;&lt;p&gt;Our modelling of anthropogenic fire adopts an approach that classifies &amp;#8216;agent functional types&amp;#8217; (AFTs) to represent human fire activity based on land use/cover and Stephen Pyne&amp;#8217;s fire development stages. For example, the &amp;#8216;swidden&amp;#8217; AFT represents shifting cultivation farmers managing cropland and secondary vegetation in a pre-industrial development setting. This approach is based on the assumption that anthropogenic fire use and management is primarily a function of land use but influenced by socio-economic context, leading different AFTs to produce qualitatively distinct fire regimes. The literature empirically supports this assumption, however data
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Journal articleKasoar M, Hamilton D, Dalmonech D, et al., 2021,
Improved estimates of future fire emissions under CMIP6 scenarios and implications for aerosol radiative forcing
<jats:p>&lt;p&gt;The CMIP6 Shared Socioeconomic Pathway (SSP) scenarios include projections of future changes in anthropogenic biomass-burning.&amp;#160; Globally, they assume a decrease in total fire emissions over the next century under all scenarios.&amp;#160; However, fire regimes and emissions are expected to additionally change with future climate, and the methodology used to project fire emissions in the SSP scenarios is opaque.&lt;/p&gt;&lt;p&gt;We aim to provide a more traceable estimate of future fire emissions under CMIP6 scenarios and evaluate the impacts for aerosol radiative forcing. &amp;#160;We utilise interactive wildfire emissions from four independent land-surface models (CLM5, JSBACH3.2, LPJ-GUESS, and ISBA-CTRIP) used within CMIP6 ESMs, and two different machine-learning methods (a random forest, and a generalised additive model) trained on historical data, to predict year 2100 biomass-burning aerosol emissions consistent with the CMIP6-modelled climate for three different scenarios: SSP126, SSP370, and SSP585.&amp;#160; This multi-method approach provides future fire emissions integrating information from observations, projections of climate, socioeconomic parameters and changes in vegetation distribution and fuel loads.&lt;/p&gt;&lt;p&gt;Our analysis shows a robust increase in fire emissions for large areas of the extra-tropics until the end of this century for all methods.&amp;#160; Although this pattern was present to an extent in the original SSP projections, both the interactive fire models and machine-learning methods predict substantially higher increases in extra-tropical emissions in 2100 than the corresponding SSP datasets.&amp;#160; Within the tropics the signal is mixed. Increases in emissions are largely driven by the temperature changes, while in some tropical areas reductions in fire emissions are
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Conference paperBaran J, Rothkaehl H, Andre N, et al., 2021,
The challenges of&#160; the Dust-Field-Plasma&#160; (DFP) instrument onboard ESA &#160;Comet Interceptor mission&#160;
<jats:p>&lt;p&gt;The&amp;#160;flyby of a dynamically new comet by ESA-F1 Comet Interceptor spacecraft offers unique multi-point&amp;#160;opportunities for studying the comet's dusty and ionised cometary &amp;#160;environment in ways that were not possible with previous missions, including Rosetta. As Comet Interceptor is an F-class mission, the payload is limited in terms of mass, power, and heritage. Most in situ science sensors therefore have been tightly integrated into a single Dust-Field-Plasma (DFP) instrument on the main spacecraft A and on the ESA sub-spacecraft B2, while there is&amp;#160;a Plasma Package suite on the&amp;#160;JAXA second sub-spacecraft B1. The advantage of tight integration is an important reduction of mass, power, and especially complexity, by keeping the electrical and data interfaces of the sensors internal to the DFP instrument.&lt;/p&gt;&lt;p&gt;The full diagnostics located on the board of the 3 spacecrafts will allow&amp;#160; to modeling the comet environment and described the complex physical processes around the comet and on their surface including also the&amp;#160; description of wave particle&amp;#160; interaction in dusty cometary plasma.&amp;#160;&lt;/p&gt;&lt;p&gt;The full set of DFP instrument&amp;#160;on &amp;#160;board the Comet Interceptor &amp;#160;spacecraft will allow&amp;#160;to model &amp;#160;the comet plasma&amp;#160;environment and&amp;#160;its interaction with the solar wind.&amp;#160;It will also allow to&amp;#160;describe&amp;#160;the complex physical processes taking place including wave particle&amp;#160;&amp;#160;interaction in dusty cometary plasma .&amp;#160;&lt;/p&gt;&lt;p&gt;On spacecraft A, DFP consists of a magne
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Conference paperStephenson P, Galand M, Deca J, et al., 2021,
Electron cooling at a weakly outgassing comet
<jats:p>&lt;p&gt;The Rosetta spacecraft arrived at comet 67P in August 2014 and then escorted it for 2 years along its orbit. Throughout this escort phase, two plasma instruments (Mutual Impedance Probe, MIP; and Langmuir Probe, LAP) measured a population of cold electrons (&lt; 1 eV) within the coma of 67P (Engelhardt et al., 2018; Wattieaux et al, 2020; Gilet et al., 2020). These cold electrons are understood to be formed by cooling warm electrons through collisions with the neutral gas. The warm electrons are primarily newly-born and produced at roughly 10eV within the coma through ionisation. While it was no surprise that cold electrons would form near perihelion given the high density of the neutral coma, the persistence of the cold electrons up to a heliocentric distance of 3.8 au was highly unexpected. With the low outgassing rates observed at such large heliocentric distances (Q &lt; 10&lt;sup&gt;26&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;), there should not be enough neutral molecules to cool the warm electrons efficiently before they ballistically escape the coma.&lt;/p&gt;&lt;p&gt;We use a collisional test particle model to examine the formation of the cold electron population at a weakly outgassing comet. The electrons are subject to stochastic collisions with the neutral coma which can either scatter or cool the electrons. Multiple electron neutral collision processes are included such that the electrons can undergo elastic scattering as well as collisions inducing excitation and ionisation of the neutral species. The inputted electric and magnetic fields, which act on the test particles, are taken from a 3D fully-kinetic, collisionless Particle-in-Cell (PiC) model of the solar wind and cometary ionosphere (Deca et al., 2017; 2019), with the same neutral coma as used in our model. We use a pure water coma with spherical sym
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Journal articleShebanits O, Hadid L, Cao H, et al., 2021,
The conductive dusty ionosphere of Saturn
<jats:p>&lt;p&gt;Cassini&amp;#8217;s Grand Finale orbits brought us historical first in-situ measurements of Saturn&amp;#8217;s ionosphere, showing that it contains dusty plasma in the equatorial region. We present the Pedersen and Hall conductivities of the top ionosphere (10:50 &amp;#8211; 12:17 Saturn Local Time, 10N &amp;#8211; 20S planetocentric latitude), derived from particle and magnetometer data. We constrain the Pedersen conductivities to be at least 10&lt;sup&gt;-5&lt;/sup&gt; &amp;#8211; 10&lt;sup&gt;-4&lt;/sup&gt; S/m at ionospheric peak, a factor 10-100 higher than estimated previously by remote measurements, while the Hall conductivities are very close to 0 or in fact negative. We show that this is an effect of dusty plasma. Another effect is that ionospheric dynamo region thickness is increased to 300-800 km. Furthermore, our results suggest a temporal variation (decrease) of the plasma densities, mean ion masses and consequently the conductivities over the period of one month.&lt;/p&gt;</jats:p>
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Conference paperThomas C, Voulgarakis A, Lim G, et al., 2021,
An unsupervised learning approach to identifying blocking events: the case of European summer
<jats:p>&lt;p&gt;Atmospheric blocking events are mid-latitude weather patterns, which obstruct the usual path of the polar jet stream. Several blocking indices (BIs) have been developed to study blocking patterns and their associated trends, but these show significant seasonal and regional differences. Despite being central features of mid-latitude synoptic-scale weather, there is no well-defined historical dataset of blocking events. Here, we introduce a new blocking index using self-organizing maps (SOMs), an unsupervised machine learning approach, and compare its detection skill to some of the most widely applied BIs. To enable this intercomparison, we first create a new ground truth time series classification of European blocking based on expert judgement. We then demonstrate that our method (SOM-BI) has several key advantages over previous BIs because it exploits all the spatial information provided in the input data and avoids the need for arbitrary thresholds. Using ERA5 reanalysis data (1979-2019), we find that the SOM-BI identifies blocking events with a higher precision and recall than other BIs. We present a case study of the 2003 European heat wave and highlight that well-defined groups of SOM nodes can be an effective tool to reliably and accurately diagnose such weather events. This contrasts with the way SOMs are commonly used, where an individual SOM node can be wrongly assumed to represent a weather pattern. We also evaluate the SOM-BI performance on about 100 years of climate model data from a preindustrial simulation with the new UK Earth System Model (UK-ESM1). For the model data, all blocking detection methods have lower skill than for the ERA5 reanalysis, but SOM-BI performs significantly better than the conventional indices. This shows that our method can be effectively applied to climate models to develop our understanding of how climate change will affect regional blocking characteristics. Overall, our results demonstra
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Journal articleKieokaew R, Lavraud B, Ruffolo D, et al., 2021,
Solar Orbiter observations of magnetic Kelvin-Helmholtz waves in the solar wind
<jats:p>&lt;p&gt;The Kelvin-Helmholtz instability (KHI) is a nonlinear shear-driven instability that develops at the interfaces between shear flows in plasmas. KHI is ubiquitous in plasmas and has been observed in situ at planetary interfaces and at the boundaries of coronal mass ejections in remote-sensing observations. KHI is also expected to develop at flow shear interfaces in the solar wind, but while it was hypothesized to play an important role in the mixing of plasmas and exciting solar wind fluctuations, its direct observation in the solar wind was still lacking. We report first in-situ observations of ongoing KHI in the solar wind using Solar Orbiter during its cruise phase. The KHI is found in a shear layer in the slow solar wind near the Heliospheric Current Sheet. We find that the observed conditions satisfy the KHI onset criterion from linear theory and the steepening of the shear boundary layer is consistent with the development of KH vortices. We further investigate the solar wind source of this event to understand the conditions that support KH growth. In addition, we set up a local MHD simulation using the empirical values to reproduce the observed KHI.&amp;#160;This observed KHI in the solar wind provides robust evidence&amp;#160;that&amp;#160;shear instability develops in the solar wind, with obvious implications in the driving of solar wind fluctuations and turbulence. The reasons for the lack of previous such measurements are also discussed.&lt;/p&gt;</jats:p>
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Journal articleStawarz J, Matteini L, Parashar T, et al., 2021,
Comparative Analysis of the Various Generalized Ohm's Law Terms in Magnetosheath Turbulence as Observed by Magnetospheric Multiscale
<jats:p>&lt;p&gt;&lt;span&gt;Electric fields (&lt;strong&gt;E&lt;/strong&gt;) play a fundamental role in facilitating the exchange of energy between the electromagnetic fields and the changed particles within a plasma. &lt;/span&gt;Decomposing &lt;strong&gt;E&lt;/strong&gt; into the contributions from the different terms in generalized Ohm's law, therefore, provides key insight into both the nonlinear and dissipative dynamics across the full range of scales within a plasma. Using the unique, high&amp;#8208;resolution, multi&amp;#8208;spacecraft measurements of three intervals in Earth's magnetosheath from the Magnetospheric Multiscale mission, the influence of the magnetohydrodynamic, Hall, electron pressure, and electron inertia terms from Ohm's law, as well as the impact of a finite electron mass, on the turbulent electric field&lt;strong&gt; &lt;/strong&gt;spectrum are examined observationally for the first time. The magnetohydrodynamic, Hall, and electron pressure terms are the dominant contributions to &lt;strong&gt;E&lt;/strong&gt; over the accessible length scales, which extend to scales smaller than the electron gyroradius at the greatest extent, with the Hall and electron pressure terms dominating at sub&amp;#8208;ion scales. The strength of the non&amp;#8208;ideal electron pressure contribution is stronger than expected from linear kinetic Alfv&amp;#233;n waves and a partial anti&amp;#8208;alignment with the Hall electric field is present, linked to the relative importance of electron diamagnetic currents within the turbulence. The relative contributions of linear and nonlinear electric fields scale with the turbulent fluctuation amplitude, with nonlinear contributions playing the dominant role in shaping &lt;strong&am
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Journal articleKilpua E, Good S, Dresing N, et al., 2021,
The sheath region of April 2020 magnetic cloud and the associated energetic ions&#160;
<jats:p>&lt;p&gt;Acceleration of energetic particles is a fundamental and ubiquitous mechanism in space and astrophysical plasmas. One of the open questions is the role of the sheath region behind the shock in the acceleration process. We analyze observations by Solar Orbiter, BepiColombo and the L1 spacecraft to explore the structure of a coronal mass ejection (CME)-driven sheath and its relation to enhancements of energetic ions that occurred on April 19-20, 2020. Our detailed analysis of the magnetic field, plasma and particle observations show that the enhancements were related to the Heliospheric Current Sheet crossings related to the reconnecting current sheets in the vicinity of the shock and a mini flux rope that was compressed at the leading edge of the CME ejecta. This study highlights the importance of smaller-scale sheath structures for the energization process. These structures likely formed already closer to the Sun and were swept and compressed from the upstream wind past the shock into the sheath. The upcoming observations by the recent missions (Solar Orbiter, Parker Solar Probe and BepiColombo) provide an excellent opportunity to explore further their role. &amp;#160;&lt;/p&gt;</jats:p>
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Journal articlePomoell J, Kilpua E, Price D, et al., 2021,
Modeling the magnetic structure of CMEs in the inner heliosphere based on data-driven time-dependent simulations of active region evolution
<jats:p>&lt;p&gt;Characterizing the detailed structure of the magnetic field in the active corona is of crucial importance for determining the chain of events from the formation to the destabilisation and subsequent eruption and propagation of coronal structures in the heliosphere. A comprehensive methodology to address these dynamic processes is needed in order to advance our capabilities to predict the properties of coronal mass ejections (CMEs) in interplanetary space and thereby for increasing the accuracy of space weather predictions. A promising toolset to provide the key missing information on the magnetic structure of CMEs are time-dependent data-driven simulations of active region magnetic fields. This methodology permits self-consistent modeling of the evolution of the coronal magnetic field from the emergence of flux to the birth of the eruption and beyond.&amp;#160;&lt;/p&gt;&lt;p&gt;In this presentation, we discuss our modeling efforts in which time-dependent data-driven coronal modeling together with heliospheric physics-based modeling are employed to study and characterize CMEs, in particular their magnetic structure, at various stages in their evolution from the Sun to Earth.&amp;#160;&lt;/p&gt;</jats:p>
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Journal articleDaei F, Pomoell J, Kilpua E, et al., 2021,
Modeling the formation and eruption of coronal structures by linking data-driven magnetofrictional and MHD simulations
<jats:p>&lt;p&gt;The time-dependent magnetofrictional model (TMFM) is a prevalent approach that has proven to be a very useful tool in the study of the formation of unstable structures in the solar corona. In particular, it is capable of incorporating observational data as initial and boundary conditions and requires shorter computational time compared to MHD simulations. To leverage the efficiency of data-driven TMFM and also to simulate eruptive events in the MHD framework, one can apply TMFM up to a certain time before the expected eruption(s) and then go on with simulation in the full or ideal MHD regime in order to more accurately capture the eruption process. However, due to the different evolution processes in these two models, using TMFM snapshots in an MHD simulation is non-trivial with several issues that need to be addressed, both physically and numerically.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;In this study, we showcase our progress in using magnetofrictional model results as input to dynamical MHD simulations. In particular, we discuss the incompatibility of the TMFM output to serve as the initial condition in MHD, and show our methods of mitigating this.&lt;/p&gt;&lt;p&gt;As our benchmark test-case, we study the evolution of NOAA active region 12673, which was previously studied using data-driven TMFM by Price et al. (2019).&lt;/p&gt;</jats:p>
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Journal articleWoolley T, Matteini L, Horbury TS, et al., 2021,
Characterisation and comparison of slow coronal hole wind intervals at 0.13au
<jats:p>&lt;p&gt;The slow solar wind is thought to consist of a component originating close to the Heliospheric Current Sheet (HCS) in the streamer belt and a component from over-expanded coronal hole boundaries. In order to understand the roles of these contributions with different origin, it is important to separate and characterise them. By exploiting the fact that Parker Solar Probe&amp;#8217;s fourth and fifth orbits were the same and the solar conditions were similar, we identify intervals of slow polar coronal hole wind sampled at approximately the same heliocentric distance and latitude. Here, solar wind properties are compared, highlighting typical conditions of the slow coronal hole wind closer to the Sun than ever before. We explore different properties of the plasma, including composition, spectra and microphysics, and discuss possible origins for the features that are observed.&lt;/p&gt;</jats:p>
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Journal articleGood S, Kilpua E, Ala-Lahti M, et al., 2021,
Cross helicity of magnetic clouds observed by Parker Solar Probe
<jats:p>&lt;p&gt;Magnetic clouds are large-scale transient structures in the solar wind with low plasma &lt;em&gt;&amp;#946;&lt;/em&gt;, low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. We analyse the normalised cross helicity, &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt;, and residual energy, &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;r&lt;/sub&gt;, in magnetic clouds observed by Parker Solar Probe (PSP). In the November 2018 cloud observed at 0.25 au, a low value of &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; was present in the cloud core, indicating that wave power parallel and anti-parallel to the mean field was approximately balanced, while the cloud&amp;#8217;s outer layers displayed larger amplitude Alfv&amp;#233;nic fluctuations with high &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; values and &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;r&lt;/sub&gt; ~ 0. These properties are compared and contrasted to those found in clouds observed by PSP at larger heliocentric distances. We suggest that low &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; is likely a common feature of magnetic clouds given their typically closed field structure, in contrast to the generally higher &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; found on the open field lines of the solar wind.&lt;/p&
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Journal articleMasters A, Dunn W, Stallard T, et al., 2021,
Low-altitude magnetic reconnection events as possible drivers of Jupiter&#8217;s polar auroras
<jats:p>&lt;p&gt;Charged particles impacting Jupiter&amp;#8217;s atmosphere represent a major energy input, generating the most powerful auroral emissions in the Solar System. Most auroral features have now been explained as the result of impacting particles accelerated by quasi-static electric fields and/or wave-particle interactions in the surrounding space environment. However, the reason for Jupiter&amp;#8217;s bright and dynamic polar regions remains a long-standing mystery. Recent spacecraft observations above these regions of &amp;#8220;swirl&amp;#8221; auroras have shown that high-energy electrons are regularly beamed away from the planet, which is inconsistent with traditional auroral drivers. The unknown downward-electron-acceleration mechanism operating close to Jupiter represents a gap in our fundamental understanding of planetary auroras. Here we propose a possible explanation for both the swirl auroras and the upward electron beams. We show that the perturbations of Jupiter&amp;#8217;s strong magnetic field above the swirl regions that are driven by dynamics of the distant space environment can cause magnetic reconnection events at altitudes as low as ~0.2 Jupiter radii, rapidly releasing energy and potentially producing both the required downward and observed upward beams of electrons. Such an auroral driver has never before been postulated, resembling physics at work in the solar corona.&lt;/p&gt;</jats:p>
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Journal articleAsvestari E, Pomoell J, Kilpua E, et al., 2021,
Constraining the CME parameters of the spheromak flux rope implemented in EUHFORIA
<jats:p>&lt;p&gt;Coronal mass ejections (CMEs) are primary drivers of space weather phenomena. Modelling the evolution of the internal magnetic field configuration of CMEs as they propagate through the interplanetary space is an essential part of space weather forecasting. EUHFORIA (EUropean Heliospheric FORecasting Information Asset) is a data-driven, physics-based model, able to trace the evolution of CMEs and CME-driven shocks through realistic background solar wind conditions. It employs a spheromak-type magnetic flux rope that is initially force-free, providing it with the advantage of modelling CME as magnetised structures. For this work we assessed the spheromak CME model employed in EUHFORIA with a test CME case study. The selected CME eruption occurred on the 6th of January 2013 and was encountered by two spacecraft, Venus Express and STEREO--A, which were radially aligned at the time of the CME passage. Our focus was to constrain the input parameters, with particular interest in: (1) translating the angular widths of the graduated cylindrical shell (GCS) fitting to the spheromak radius, and (2) matching the observed magnetic field topology at the source region. We ran EUHFORIA with three different spheromak radii. The model predicts arrival times from half to a full day ahead of the one observed &lt;em&gt;in situ&lt;/em&gt;. We conclude that the choice of spheromak radius affected the modelled magnetic field profiles, their amplitude, arrival times, and sheath region length.&lt;/p&gt;</jats:p>
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Journal articleChen C, Chandran B, Woodham L, et al., 2021,
The Near-Sun Streamer Belt Solar Wind: Turbulence and Solar Wind Acceleration
<jats:p>&lt;p&gt;The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances down to 27.9 Rs, allowing solar wind turbulence and acceleration mechanisms to be studied in situ closer to the Sun than previously possible. The turbulence properties were found to be significantly different in the inbound and outbound portions of PSP's fourth solar encounter, likely due to the proximity to the heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the streamer belt wind, the turbulence was found to have lower amplitudes, higher magnetic compressibility, a steeper magnetic field spectrum (with spectral index close to -5/3 rather than -3/2), a lower Alfvenicity, and a &quot;1/f&quot; break at much lower frequencies. These are also features of slow wind at 1 au, suggesting the near-Sun streamer belt wind to be the prototypical slow solar wind. The transition in properties occurs at a predicted angular distance of ~4 degrees from the HCS, suggesting ~8 degrees as the full-width of the streamer belt wind at these distances. While the majority of the Alfvenic turbulence energy fluxes measured by PSP are consistent with those required for reflection-driven turbulence models of solar wind acceleration, the fluxes in the streamer belt are significantly lower than the model predictions, suggesting that additional mechanisms are necessary to explain the acceleration of the streamer belt solar wind.&lt;/p&gt;</jats:p>
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Journal articleVoigt A, Albern N, Ceppi P, et al., 2021,
Clouds, radiation, and atmospheric circulation in the present-day climate and under climate change
, Wiley Interdisciplinary Reviews: WIREs Climate Change, Vol: 12, Pages: 1-22, ISSN: 1757-7780By interacting with radiation, clouds modulate the flow of energy through the Earth system, the circulation of the atmosphere, and regional climate. We review the impact of cloud‐radiation interactions for the atmospheric circulation in the present‐day climate, its internal variability and its response to climate change. After summarizing cloud‐controlling factors and cloud‐radiative effects, we clarify the scope and limits of the Clouds On‐Off Klimate Model Intercomparison Experiment (COOKIE) and cloud‐locking modeling methods. COOKIE showed that the presence of cloud‐radiative effects shapes the circulation in the present‐day climate in many important ways, including the width of the tropical rain belts and the position of the extratropical storm tracks. Cloud locking, in contrast, identified how clouds affect internal variability and the circulation response to global warming. This includes strong, but model‐dependent, shortwave and longwave cloud impacts on the El‐Nino Southern Oscillation, and the finding that most of the poleward circulation expansion in response to global warming can be attributed to radiative changes in clouds. We highlight the circulation impact of shortwave changes from low‐level clouds and longwave changes from rising high‐level clouds, and the contribution of these cloud changes to model differences in the circulation response to global warming. The review in particular draws attention to the role of cloud‐radiative heating within the atmosphere. We close by raising some open questions which, among others, concern the need for studying the cloud impact on regional scales and opportunities created by the next generation of global storm‐resolving models.
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Journal articleKlein KG, Verniero JL, Alterman B, et al., 2021,
Inferred Linear Stability of Parker Solar Probe Observations Using One- and Two-component Proton Distributions
, ASTROPHYSICAL JOURNAL, Vol: 909, ISSN: 0004-637X- Author Web Link
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- Citations: 19
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Journal articleWang L, Zong Q, Shi Q, et al., 2021,
Solar Energetic Electrons Entering the Earth's Cusp/Lobe
, ASTROPHYSICAL JOURNAL, Vol: 910, ISSN: 0004-637X -
Journal articleHe J, Cui B, Yang L, et al., 2021,
The Encounter of the Parker Solar Probe and a Comet-like Object Near the Sun: Model Predictions and Measurements
, ASTROPHYSICAL JOURNAL, Vol: 910, ISSN: 0004-637X- Author Web Link
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- Citations: 2
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