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Journal articleFuselier SA, Petrinec SM, Reiff PH, et al., 2024,
Global-scale processes and effects of magnetic reconnection on the geospace environment
, Space Science Reviews, Vol: 220, ISSN: 0038-6308Recent multi-point measurements, in particular from the Magnetospheric Multiscale (MMS)spacecraft, have advanced the understanding of micro-scale aspects of magnetic reconnection. In addition, the MMS mission, as part of the Heliospheric System Observatory, combined with recent advances in global magnetospheric modeling, have furthered the understanding of meso- and global-scale structure and consequences of reconnection. Magneticreconnection at the dayside magnetopause and in the magnetotail are the drivers of the globalDungey cycle, a classical picture of global magnetospheric circulation. Some recent advances in the global structure and consequences of reconnection that are addressed hereinclude a detailed understanding of the location and steadiness of reconnection at the dayside magnetopause, the importance of multiple plasma sources in the global circulation, andreconnection consequences in the magnetotail. These advances notwithstanding, there areimportant questions about global reconnection that remain. These questions focus on howmultiple reconnection and reconnection variability fit into and complicate the Dungey Cyclepicture of global magnetospheric circulation.
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Journal articleHietala H, Trotta D, Fedeli A, et al., 2024,
Candidates for downstream jets at interplanetary shocks
, Monthly Notices of the Royal Astronomical Society, ISSN: 0035-8711<jats:title>Abstract</jats:title> <jats:p>Localised dynamic pressure enhancements arising from kinetic processes are frequently observed downstream of the Earth’s bow shock. These structures, called jets, modify their plasma surroundings and participate in particle energisation. Here, we report the first observations of jet-like structures at a non-planetary shock environment: downstream of interplanetary shocks. We introduce an analysis approach suitable for such conditions and apply it to Wind spacecraft data. We present one event with a Mach number similar to the Earth’s bow shock as a benchmark, as well as two low Mach number, low beta shocks: a parameter range that is difficult to access at planets. The jet-like structures we find are tens of ion inertial lengths in size, and some are observed further away from the shock than in a limited magnetosheath. We find that their properties are similar to those of magnetosheath jets: in the frame of the shock these structures are fast, cold, and most have no strong magnetic field variations. All three interplanetary shocks feature foreshock activity, but no strongly compressive waves. We discuss the implications these findings have for the proposed jet formation mechanisms.</jats:p>
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Journal articlePerkins O, Kasoar M, Voulgarakis A, et al., 2024,
A global behavioural model of human fire use and management: WHAM! v1.0
, Geoscientific Model Development, Vol: 17, Pages: 3993-4016<jats:p>Abstract. Fire is an integral ecosystem process and a major natural source of vegetation disturbance globally. Yet at the same time, humans use and manage fire in diverse ways and for a huge range of purposes. Therefore, it is perhaps unsurprising that a central finding of the first Fire Model Intercomparison Project was simplistic representation of humans is a substantial shortcoming in the fire modules of dynamic global vegetation models (DGVMs). In response to this challenge, we present a novel, global geospatial model that seeks to capture the diversity of human–fire interactions. Empirically grounded with a global database of anthropogenic fire impacts, WHAM! (the Wildfire Human Agency Model) represents the underlying behavioural and land system drivers of human approaches to fire management and their impact on fire regimes. WHAM! is designed to be coupled with DGVMs (JULES-INFERNO in the current instance), such that human and biophysical drivers of fire on Earth, and their interactions, can be captured in process-based models for the first time. Initial outputs from WHAM! presented here are in line with previous evidence suggesting managed anthropogenic fire use is decreasing globally and point to land use intensification as the underlying reason for this phenomenon. </jats:p>
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Journal articleOpgenoorth HJ, Robinson R, Ngwira CM, et al., 2024,
Earth’s geomagnetic environment—progress and gaps in understanding, prediction, and impacts
, Advances in Space Research, ISSN: 0273-1177Understanding of Earth’s geomagnetic environment is critical to mitigating the space weather impacts caused by disruptive geoelectric fields in power lines and other conductors on Earth’s surface. These impacts are the result of a chain of processes driven by the solar wind and linking Earth’s magnetosphere, ionosphere, thermosphere and Earth’s surface. Tremendous progress has been made over the last two decades in understanding the solar wind driving mechanisms, the coupling mechanisms connecting the magnetically controlled regions of near-Earth space, and the impacts of these collective processes on human technologies on Earth’s surface. Studies of solar wind drivers have been focused on understanding the responses of the geomagnetic environment to spatial and temporal variations in the solar wind associated with Coronal Mass Ejections, Corotating Interaction Regions, Interplanetary Shocks, High-Speed Streams, and other interplanetary magnetic field structures. Increasingly sophisticated numerical models are able to simulate the magnetospheric response to the solar wind forcing associated with these structures. Magnetosphere-ionosphere-thermosphere coupling remains a great challenge, although new observations and sophisticated models that can assimilate disparate data sets have improved the ability to specify the electrodynamic properties of the high latitude ionosphere. The temporal and spatial resolution needed to predict the electric fields, conductivities, and currents in the ionosphere is driving the need for further advances. These parameters are intricately tied to auroral phenomena—energy deposition due to Joule heating and precipitating particles, motions of the auroral boundary, and ion outflow. A new view of these auroral processes is emerging that focuses on small-scale structures in the magnetosphere and their ionospheric effects, which may include the rapid variations in current associated with geomagnetically indu
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Conference paperRothkaehl H, Andre N, Auster U, et al., 2024,
Dust, Field and Plasma instrument onboard ESA&#8217;s Comet Interceptor &#160;mission
<jats:p>The main goal of ESA&#8217;s F-1 class Comet Interceptor mission is to characterise, for the first time, a long period comet; preferably a dynamically-new or an interstellar object. The main spacecraft, will have its trajectory outside of the inner coma, whereas two sub-spacecrafts will be targeted inside the inner coma, closer to the nucleus. The flyby of such a comet &#160;will offer unique multipoint measurement opportunity to study the comet's dusty and ionised environment in ways exceeding that of the previous cometary missions, including Rosetta.&#160;The Dust Field and Plasma (DFP) instruments located on both the main spacecraft A and on the sub-spacecraft B2, is a combined experiment dedicated to the in situ, multi-point study of the multi-phased ionized and dusty environment in the coma of the target and &#160;its interaction with the surrounding space environment and the Sun.&#160;The DFP instruments will be present in different configurations on the Comet Interceptor spacecraft A and B2. To enable the measurements on spacecraft A, the DFP is composed of 5 sensors; Fluxgate magnetometer DFP-FGM-A, Plasma instrument with nanodust and E-field measurements capabilities DFP-COMPLIMENT, Electron spectrometer DFP-LEES, Ion and energetic neutrals spectrometer DFP-SCIENA &#160;and Dust detector DFP-DISC. On board of spacecraft B2 the DFP is composed of 2 sensors: Fluxgate magnetometer DFP-FGM-B2 and Cometary dust detector DFP-DISC.&#160;The DFP instrument will measure magnetic field, the electric field, plasma parameters (density, temperature, speed), the distribution functions of electrons, ions and energetic neutrals, spacecraft potential, mass, number and spatial density of cometary dust particles and the dust impacts. &#160;&#160;The full set of DFP sensors will allow to model the comet plasma environment and its interaction with the solar wind. It will also allow to describe
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Conference paperStephenson P, Galand M, Deca J, et al., 2024,
Forming a cold electron population at a weakly outgassing comet
<jats:p>The Rosetta Mission rendezvoused with comet 67P/Churyumov-Gerasimenko in August 2014 and escorted it for two years along its orbit. The Rosetta Plasma Consortium (RPC) was a suite of instruments, which observed the plasma environment at the spacecraft throughout the escort phase. The Mutual Impedance Probe (RPC/MIP; Wattieaux et al, 2020; Gilet et al., 2020) and Langmuir Probe (RPC/LAP; Engelhardt et al., 2018), both part of RPC, measured the presence of a cold electron population within the coma.Newly born electrons, generated by ionisation of the neutral gas, form a warm population within the coma at ~10eV. Ionisation is either through absorption of extreme ultraviolet photons or through collisions of energetic electrons with the neutral molecules. The cold electron population is formed by cooling the newly born, warm electrons via electron-neutral collisions. Assuming the radial outflow of electrons, the cold population was only expected at comet 67P close to perihelion, where outgassing rate from the nucleus was at its highest (Q > 1028 s-1). However, cold electrons were observed until the end of the Rosetta mission at 3.8au when the outgassing was weak (Q</jats:p>
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Conference paperStephenson P, Galand M, Deca J, et al., 2024,
Cooling of Electrons in a Weakly Outgassing Comet
<jats:p>The plasma instruments, Mutual Impedance Probe (MIP) and Langmuir Probe (LAP), part of the Rosetta Plasma Consortium (RPC), onboard the Rosetta mission to comet 67P revealed a population of cold electrons (</jats:p>
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Journal articleProvan G, Bradley T, Bunce E, et al., 2024,
Saturn&#8217;s nightside ring current during Cassini&#8217;s Grand Finale
<jats:p>During Cassini&#8217;s Grand Finale proximal orbits, the spacecraft traversed the nightside magnetotail to ~21 Saturn radii. &#160;Clear signatures of Saturn&#8217;s equatorial current sheet are observed in the magnetic field data. &#160;An axisymmetric model of the ring current is fitted to these data, amended to taken into account the tilt of the current layer by solar wind forcing, its teardrop-shaped nature and the magnetotail and magnetopause fringing fields. &#160;Variations in ring current parameters are examined in relation to external driving of the magnetosphere by the solar wind, and internal driving by the two planetary period oscillations (PPOs) and compared with dawn and dayside regimes. &#160;The relative phasing of the PPOs determines the ring current&#8217;s response to solar wind conditions. During solar wind compressions when the PPOS are in antiphase, magnetospheric storms are triggered and a thick partial ring current is formed on the nightside, dominated by hot plasma injected by tail reconnection.&#160; However, during solar wind compressions when the PPOs are in phase, the magnetosphere shows only a &#8216;minor&#8217; response and a partial ring current is not observed. During solar wind rarefactions an equatorial &#8216;magnetodisc&#8217; configuration is observed in the dayside/dawn/nightside regions, with similar total currents flowing at these local times. &#160;This partial ring current should close partly via magnetopause currents and possibly via field-aligned currents into the ionosphere. &#160;During very quiet intervals of prolonged solar wind rarefaction, a thin current sheet with an enhanced current density is formed, indicative of a ring current dominated by cool, dense, Enceladus water group ions.</jats:p>
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Journal articleCohen CMS, Leske RA, Christian ER, et al., 2024,
Observations of the 2022 September 5 Solar Energetic Particle Event at 15 Solar Radii
, Astrophysical Journal, Vol: 966, ISSN: 0004-637XOn 2022 September 5, Parker Solar Probe (Parker) observed a large solar energetic particle (SEP) event at the unprecedented distance of only 15 R S from the Sun. The observations from the Integrated Science Investigation of the Sun (IS⊙IS) obtained over the course of this event are remarkably rich, and an overview is presented here. IS⊙IS is capable of measuring ions from 20 keV to over 100 MeV nuc−1 and electrons from 30 keV to 6 MeV; here, we primarily focus on the proton and helium measurements above 80 keV. Among the surprising results are evidence of inverse velocity dispersion at energies above 1 MeV during the onset of the event, a sharp decrease in the energetic particle intensities at all energies at the interplanetary shock crossing, and repeated short durations of highly anisotropic sunward flow. Many changes in the SEP intensities, anisotropy, and spectral steepness are coincident with solar wind structure boundaries identified using the Parker solar wind magnetic field and plasma data. However, there are significant changes that are not correlated with any clearly visible solar wind variation. The observations presented here serve as an introduction to a complex event with numerous opportunities for future, more in-depth studies.
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Journal articleDe Keyser J, Edberg NJT, Henri P, et al., 2024,
In situ plasma and neutral gas observation time windows during a comet flyby: Application to the Comet Interceptor mission
, Planetary and Space Science, Vol: 244, ISSN: 0032-0633A comet flyby, like the one planned for ESA's Comet Interceptor mission, places stringent requirements on spacecraft resources. To plan the time line of in situ plasma and neutral gas observations during the flyby, the size of the comet magnetosphere and neutral coma must be estimated well. For given solar irradiance and solar wind conditions, comet composition, and neutral gas expansion speed, the size of gas coma and magnetosphere during the flyby can be estimated from the gas production rate and the flyby geometry. Combined with flyby velocity, the time spent in these regions can be inferred and a data acquisition plan can be elaborated for each instrument, compatible with the limited data storage capacity. The sizes of magnetosphere and gas coma are found from a statistical analysis based on the probability distributions of gas production rate, flyby velocity, and solar wind conditions. The size of the magnetosphere as measured by bow shock standoff distance is 105–106 km near 1 au in the unlikely case of a Halley-type target comet, down to a nonexistent bow shock for targets with low activity. This translates into durations up to 103–104 seconds. These estimates can be narrowed down when a target is identified far from the Sun, and even more so as its activity can be predicted more reliably closer to the Sun. Plasma and neutral gas instruments on the Comet Interceptor main spacecraft can monitor the entire flyby by using an adaptive data acquisition strategy in the context of a record-and-playback scenario. For probes released from the main spacecraft, the inter-satellite communication link limits the data return. For a slow flyby of an active comet, the probes may not yet be released during the inbound bow shock crossing.
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Journal articleZank GP, Zhao LL, Adhikari L, et al., 2024,
Characterization of Turbulent Fluctuations in the Sub-Alfvénic Solar Wind
, Astrophysical Journal, Vol: 966, ISSN: 0004-637XParker Solar Probe (PSP) observed sub-Alfvénic solar wind intervals during encounters 8-14, and low-frequency magnetohydrodynamic (MHD) turbulence in these regions may differ from that in super-Alfvénic wind. We apply a new mode decomposition analysis to the sub-Alfvénic flow observed by PSP on 2021 April 28, identifying and characterizing entropy, magnetic islands, forward and backward Alfvén waves, including weakly/nonpropagating Alfvén vortices, forward and backward fast and slow magnetosonic (MS) modes. Density fluctuations are primarily and almost equally entropy- and backward-propagating slow MS modes. The mode decomposition provides phase information (frequency and wavenumber k) for each mode. Entropy density fluctuations have a wavenumber anisotropy of k ∥ ≫ k ⊥, whereas slow-mode density fluctuations have k ⊥ > k ∥. Magnetic field fluctuations are primarily magnetic island modes (δ B i ) with an O(1) smaller contribution from unidirectionally propagating Alfvén waves (δ B A+) giving a variance anisotropy of 〈 δ B i 2 〉 / 〈 δ B A 2 〉 = 4.1 . Incompressible magnetic fluctuations dominate compressible contributions from fast and slow MS modes. The magnetic island spectrum is Kolmogorov-like k ⊥ − 1.6 in perpendicular wavenumber, and the unidirectional Alfvén wave spectra are k ∥ − 1.6 and k ⊥ − 1.5 . Fast MS modes propagate at essentially the Alfvén speed with anticorrelated transverse velocity and magnetic field fluctuations and are almost exclusively magnetic due to β p ≪ 1. Transverse velocity fluctuations are the dominant velocity component in fast MS modes, and longitudinal fluctuations dominate in slow modes. Mode decomposition is an effective tool in identifying the basic building blocks of MHD turbulence and provides detailed phase information about each of the modes.
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Journal articleGuo X, Wang L, Li W, et al., 2024,
Evolution of Electron Acceleration by Corotating Interaction Region Shocks at 1 au
, Astrophysical Journal Letters, Vol: 966, ISSN: 2041-8205We present the first observations of in situ electron acceleration at corotating interaction region (CIR) shocks near 1 au, utilizing measurements from Wind and Magnetospheric Multiscale (MMS) mission in the interplanetary medium. As the forward (reverse) shock of the 2018 January CIR (the 2020 February CIR) moves from Wind at [206, 92, −7]R E ([257, 25, 3]R E ) to MMS1 at [24, 2, 7]R E ([25, 3, 0.5]R E ), the shock’s thickness becomes 8 (3) times thinner, but the convective electric field E drift gets weaker (stronger) along the shock; both the upstream and shocked suprathermal electrons exhibit a flatter flux energy spectrum, while the electron shock acceleration becomes less (more) significant. For the shocked suprathermal electrons with significant flux enhancement, the flux ratio across the shock appears to peak in the direction perpendicular to the magnetic field. Therefore, the CIR shock acceleration of solar wind suprathermal electrons at 1 au exhibits an efficiency increasing with the E drift strength. These results also suggest that such acceleration through the interplanetary medium can contribute to the formation of solar wind suprathermal electrons.
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Journal articleToledo-Redondo S, Lee JH, Vines SK, et al., 2024,
Statistical Observations of Proton-Band Electromagnetic Ion Cyclotron Waves in the Outer Magnetosphere: Full Wavevector Determination
, Journal of Geophysical Research: Space Physics, Vol: 129, ISSN: 2169-9380Electromagnetic Ion Cyclotron (EMIC) waves mediate energy transfer from the solar wind to the magnetosphere, relativistic electron precipitation, or thermalization of the ring current population, to name a few. How these processes take place depends on the wave properties, such as the wavevector and polarization. However, inferring the wavevector from in-situ measurements is problematic since one needs to disentangle spatial and time variations. Using 8 years of Magnetospheric Multiscale (MMS) mission observations in the dayside magnetosphere, we present an algorithm to detect proton-band EMIC waves in the Earth's dayside magnetosphere, and find that they are present roughly 15% of the time. Their normalized frequency presents a dawn-dusk asymmetry, with waves in the dawn flank magnetosphere having larger frequency than in the dusk, subsolar, and dawn near subsolar region. It is shown that the observations are unstable to the ion cyclotron instability. We obtain the wave polarization and wavevector by comparing Single Value Decomposition and Ampere methods. We observe that for most waves the perpendicular wavenumber (k⊥) is larger than the inverse of the proton gyroradius (ρi), that is, k⊥ρi > 1, while the parallel wavenumber is smaller than the inverse of the ion gyroradius, that is, k‖ρi < 1. Left-hand polarized waves are associated with small wave normal angles (θBk < 30°), while linearly polarized waves are associated with large wave normal angles (θBk > 30°). This work constitutes, to our knowledge, the first attempt to statistically infer the full wavevector of proton-band EMIC waves observed in the outer magnetosphere.
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Journal articleLewis ZM, Beth A, Galand M, et al., 2024,
Constraining ion transport in the diamagnetic cavity of comet 67P
, Monthly Notices of the Royal Astronomical Society, Vol: 530, Pages: 66-81, ISSN: 0035-8711The European Space Agency Rosetta mission escorted comet 67P for a 2-yr section of its six and a half-year orbit around the Sun. By perihelion in 2015 August, the neutral and plasma data obtained by the spacecraft instruments showed the comet had transitioned to a dynamic object with large-scale plasma structures and a rich ion environment. One such plasma structure is the diamagnetic cavity: a magnetic field-free region formed by interaction between the unmagnetized cometary plasma and the impinging solar wind. Within this re gion, une xpectedly high ion bulk velocities have been observed, thought to have been accelerated by an ambipolar electric field. We hav e dev eloped a 1D numerical model of the cometary ionosphere to constrain the impact of various electric field profiles on the ionospheric density profile and ion composition. In the model, we include three ion species: H 2 O + , H 3 O + , and NH + 4 . The latter, not previously considered in ionospheric models including acceleration, is produced through the protonation of NH 3 and only lost through ion-electron dissociative recombination, and thus particularly sensitive to the time-scale of plasma loss through transport. We also assess the importance of including momentum transfer when assessing ion composition and densities in the presence of an electric field. By comparing simulated electron densities to Rosetta Plasma Consortium data sets, we find that to recreate the plasma densities measured inside the diamagnetic cavity near perihelion, the model requires an electric field proportional to r -1 of around 0.5-2 mV m -1 surface strength, leading to bulk ion speeds at Rosetta of 1.2-3.0 km s -1 .
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Journal articleArcher M, Pilipenko V, Li B, et al.,
Magnetopause MHD Surface Wave Theory: Progress & Challenges
, Frontiers in Astronomy and Space Sciences, ISSN: 2296-987X -
Journal articleZhou Y, He F, Archer MO, et al., 2024,
Spatial evolution characteristics of plasmapause surface wave during a geomagnetic storm on 16 July 2017
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276Boundary dynamics are crucial for the transport of energy, mass, and momentum in geospace. The recently discovered plasmapause surface wave (PSW) plays a key role in the inner magnetosphere dynamics. However, a comprehensive investigation of spatial variations of the PSW remains absent. In this study, we elucidate the spatial characteristics of a PSW through observations from multiple spacecrafts in the magnetosphere. Following the initiation of the PSW, quasi-periodic injections of energetic ions, rather than electrons, are suggested to serve as energy source of the PSW. Based on the distinct wave and particle signatures, we categorize the PSW into four regions: seed region, growth region, stabilization region and decay region, spanning from nightside to afternoon plasmapause. These findings advance our understanding of universal boundary dynamics and contribute to a deeper comprehension of the pivotal roles of surface waves in the energy couplings within the magnetosphere-plasmasphere-ionosphere system.
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ReportZachariah M, Kimutai J, Barnes C, et al., 2024,
Heavy precipitation hitting vulnerable communities in the UAE and Oman becoming an increasing threat as the climate warms
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Journal articleSparks N, Toumi R, 2024,
The Imperial College Storm model (IRIS) dataset
, Scientific Data, Vol: 11, ISSN: 2052-4463Assessing tropical cyclone risk on a global scale given the infrequency of landfalling tropical cyclones (TC) and the short period of reliable observations remains a challenge. Synthetic tropical cyclone datasets can help overcome these problems. Here we present a new global dataset created by IRIS, the ImpeRIal college Storm model. IRIS is novel because, unlike other synthetic TC models, it only simulates the decay from the point of lifetime maximum intensity. This minimises the bias in the dataset. It takes input from 42 years of observed tropical cyclones and creates a 10,000 year synthetic dataset of wind speed which is then validated against the observations. IRIS captures important statistical characteristics of the observed data. The return periods of the landfall maximum wind speed are realistic globally.
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Journal articleBlackford K, Kasoar M, Burton C, et al., 2024,
INFERNO-peat v1.0.0: a representation of northern high latitude peat fires in the JULES-INFERNO global fire model
, Geoscientific Model Development, Vol: 17, Pages: 3063-3079, ISSN: 1991-959XPeat fires in the northern high latitudes have the potential to burn vast amounts of carbon-rich organic soil, releasing large quantities of long-term stored carbon to the atmosphere. Due to anthropogenic activities and climate change, peat fires are increasing in frequency and intensity across the high latitudes. However, at present they are not explicitly included in most fire models. Here we detail the development of INFERNO-peat, the first parameterization of peat fires in the JULES-INFERNO (Joint UK Land Environment Simulator INteractive Fire and Emission algoRithm for Natural envirOnments) fire model. INFERNO-peat utilizes knowledge from lab and field-based studies on peat fire ignition and spread to be able to model peat burnt area, burn depth, and carbon emissions, based on data of the moisture content, inorganic content, bulk density, soil temperature, and water table depth of peat. INFERNO-peat improves the representation of burnt area in the high latitudes, with peat fires simulating on average an additional 0.305×106 km2 of burn area each year, emitting 224.10 Tg of carbon. Compared to Global Fire Emissions Database version 5 (GFED5), INFERNO-peat captures ∼ 20 % more burnt area, whereas INFERNO underestimated burning by 50 %. Additionally, INFERNO-peat substantially improves the representation of interannual variability in burnt area and subsequent carbon emissions across the high latitudes. The coefficient of variation in carbon emissions is increased from 0.071 in INFERNO to 0.127 in INFERNO-peat, an almost 80 % increase. Therefore, explicitly modelling peat fires shows a substantial improvement in the fire modelling capabilities of JULES-INFERNO, highlighting the importance of representing peatland systems in fire models.
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Journal articleMitchell DG, Hill ME, McComas DJ, et al., 2024,
Likely Common Coronal Source of Solar Wind and <sup>3</sup>He-enriched Energetic Particles: Uncoupled Transport from the Low Corona to 0.2 au
, Astrophysical Journal, Vol: 965, ISSN: 0004-637XParker Solar Probe (PSP) observations of a small dispersive event on 2022 February 27 and 28 indicate scatter-free propagation as the dominant transport mechanism between the low corona and greater than 35 solar radii. The event occurred during unique orbital conditions that prevailed along specific flux tubes that PSP encountered repeatedly between 25 and 35 Rs during outbound orbit 11. This segment of the PSP orbit exhibits almost stationary angular motion relative to the rotating solar surface, such that in the rotating frame, PSP’s motion is essentially radial. The time dispersion often observed in impulsive solar energetic particle (SEP) events continues in this case down to velocities including the core solar-wind ion velocities. Especially at the onset of this event, the 3He content is much larger than the usual SEP abundances seen in the energy range from ∼100 keV to several MeV for helium. Later in the event, iron is enhanced. The compositional signatures suggest this to be an example of an acceleration mechanism for generating the seed energetic particles required by shock (or compression) acceleration models in SEP events to account for the enrichment of various species above solar abundances in such events. A preliminary search of similar orbital conditions over the PSP mission has not revealed additional such events, although favorable conditions (isolated impulsive acceleration and well-ordered magnetic field connection with minimal magnetic field fluctuation) that would be required are infrequently realized, given the small fraction of the PSP trajectory that meets these observation conditions.
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Journal articleStephenson P, Galand M, Deca J, et al., 2024,
Cold electrons at a weakly outgassing comet
, Monthly Notices of the Royal Astronomical Society, Vol: 529, Pages: 2854-2865, ISSN: 0035-8711Throughout the Rosetta mission, cold electrons (<1 eV) were measured in the coma of comet 67P/Churyumov–Gerasimenko. Cometary electrons are produced at ∼10 eV through photoionization or through electron-impact ionization collisions. The cold electron population is formed by cooling the warm population through inelastic electron–neutral collisions. Assuming radial electron outflow, electrons are collisional with the neutral gas coma below the electron exobase, which only formed above the comet surface in near-perihelion high-outgassing conditions (Q > 3 × 1027 s−1). However, the cold population was identified at low outgassing (Q < 1026 s−1), when the inner coma was not expected to be collisional. We examine cooling of electrons at a weakly outgassing comet, using a 3D collisional model of electrons at a comet. Electron paths are extended by trapping in an ambipolar electric field and by gyration around magnetic field lines. This increases the probability of electrons undergoing inelastic collisions with the coma and becoming cold. We demonstrate that a cold electron population can be formed and sustained, under weak outgassing conditions (Q = 1026 s−1), once 3D electron dynamics are accounted for. Cold electrons are produced in the inner coma through electron–neutral collisions and transported tailwards by an E × B drift We quantify the efficiency of trapping in driving electron cooling, with trajectories typically 100 times longer than expected from ballistic radial outflow. Based on collisional simulations, we define an estimate for a region where a cold electron population can form, bounded by an electron cooling exobase. This estimate agrees well with cold electron measurements from the Rosetta Plasma Consortium.
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Journal articleHellinger P, Verdini A, Montagud-Camps V, et al., 2024,
Anisotropy of plasma turbulence at ion scales: Hall and pressure-strain effects
, Astronomy and Astrophysics, Vol: 684, ISSN: 0004-6361Aims. We investigated the properties of plasma turbulence at ion scales in the solar wind context. We concentrated on the behaviour of the Hall physics and the pressure strain interaction and their anisotropy owing to the ambient magnetic field. Methods. We studied the results of a three-dimensional hybrid simulation of decaying plasma turbulence using the Kármán-Howarth-Monin (KHM) equation, which quantifies different turbulent processes. Results. The isotropised KHM analysis shows that kinetic plus magnetic (kinetic+magnetic) energy decays at large scales; this energy cascades from large to small scales via the magneto-hydrodynamic non-linearity that is partly continued via the Hall coupling around the ion scales. The cascading kinetic+magnetic energy is partly dissipated at small scales via resistive dissipation. This standard dissipation is complemented by the pressure-strain interaction, which plays the role of an effective dissipation mechanism and starts to act at relatively large scales. The pressure-strain interaction has two components, compressive and incompressive. Compressive interaction is connected with the velocity dilatation, which mostly reversibly exchanges kinetic+magnetic and internal energies. Incompressive interaction mostly irreversibly converts the kinetic+magnetic energy to internal energy. The compressive effects lead to important oscillations of the turbulence properties, but the compressibility is strongly reduced when averaged over a time period spanning a few periods of the oscillations. The ambient magnetic field induces a strong spectral anisotropy. The turbulent fluctuations exhibit larger scales along the magnetic field compared to the perpendicular directions. The KHM results show the corresponding anisotropy of turbulent processes: their characteristic scales shift to larger scales in the quasi-parallel direction with respect to the ambient magnetic field compared to the quasi-perpendicular direction. This anisotrop
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Journal articleDing M, Ryabtsev AN, Kononov EY, et al., 2024,
Spectrum and energy levels of the low-lying configurations of Nd III
, Astronomy and Astrophysics, Vol: 684, ISSN: 0004-6361Aims. Our goal is to accurately determine bound-to-bound transition wavelengths and energy levels of the low-lying open-shell configurations 4f4, 4f3 5d, 4f36s, and 4f3 6p of doubly ionised neodymium (Nd III) through high-resolution spectroscopy and semi-empirical calculations. Methods. The emission spectra of neodymium (Nd, Z = 60) were recorded using Penning and hollow cathode discharge lamps in the region 11 500-54000 cm-1 (8695-1852 A) by Fourier transform spectroscopy at resolving powers up to 106. Wavenumber measurements were accurate to a few 10-3 cm-1. Grating spectroscopy of Nd vacuum sliding sparks and stellar spectra were used to aid line and energy level identification. For the analysis, new Nd III atomic structure and transition probability calculations were carried out using the Cowan code parameterised by newly established levels. Results. The classification of 432 transitions of Nd III from the Penning lamp spectra resulted in the determination of 144 energy levels of the 4f4, 4f3 5d, 4f3 6s, and 4f3 6p configurations of Nd III, 105 of which were experimentally established for the first time. Of the 40 previously published Nd III levels, one was revised and 39 were confirmed. Conclusions. The results will not only benchmark and improve future semi-empirical atomic structure calculations of Nd III, but also enable more reliable astrophysical applications of Nd III, such as abundance analyses of kilonovae and chemically peculiar stars, and studies of pulsational wave propagation in these stars.
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Journal articleEriksson S, Swisdak M, Mallet A, et al., 2024,
Parker Solar Probe Observations of Magnetic Reconnection Exhausts in Quiescent Plasmas near the Sun
, Astrophysical Journal, Vol: 965, ISSN: 0004-637XParker Solar Probe observations are analyzed for the presence of reconnection exhausts across current sheets (CSs) within R < 0.26 au during encounters 4-11. Exhausts are observed with nearly equal probability at all radial distances with a preference for quiescent Tp < 0.80 MK plasmas typical of a slow-wind regime. High Tp > 0.80 MK plasmas of a fast wind characterized by significant transverse fluctuations rarely support exhausts irrespective of the CS width. Exhaust observations demonstrate the presence of local temperature gradients across several CSs with a higher-Tp plasma on locally closed fields and a lower-Tp plasma on locally open field lines for an interchange-type reconnection. A CS geometry analysis directly supports the property that X-lines bisect the magnetic field rotation θ-angle, whether the fields and plasmas are asymmetric or not, to maximize reconnection rates and available magnetic energy. The CS normal width d cs distributions suggest that a multiscale reconnection process through nested layers of bifurcated CSs may be responsible for observed power-law distributions beyond the median d cs ∼ 1000 km with an exponential d cs distribution present for ion kinetic dissipation scales below this median. Magnetic field shear θ-angles are essentially identical at R < 0.26 and 1 au with medians at θ ∼ 55° near the Sun and θ ∼ 65° at 1 au. In contrast, the tangential flow shear distributions are different near and far from the Sun. A bimodal flow shear angle distribution is present near the Sun with strong shear flow magnitudes. This distribution is modified with radial distance toward a relatively flat distribution of weaker flow shear magnitudes.
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Journal articleFiedler S, Naik V, O'Connor FM, et al., 2024,
Interactions between atmospheric composition and climate change - progress in understanding and future opportunities from AerChemMIP, PDRMIP, and RFMIP
, Geoscientific Model Development, Vol: 17, Pages: 2387-2417, ISSN: 1991-959XThe climate science community aims to improve our understanding of climate change due to anthropogenic influences on atmospheric composition and the Earth's surface. Yet not all climate interactions are fully understood, and uncertainty in climate model results persists, as assessed in the latest Intergovernmental Panel on Climate Change (IPCC) assessment report. We synthesize current challenges and emphasize opportunities for advancing our understanding of the interactions between atmospheric composition, air quality, and climate change, as well as for quantifying model diversity. Our perspective is based on expert views from three multi-model intercomparison projects (MIPs) - the Precipitation Driver Response MIP (PDRMIP), the Aerosol Chemistry MIP (AerChemMIP), and the Radiative Forcing MIP (RFMIP). While there are many shared interests and specializations across the MIPs, they have their own scientific foci and specific approaches. The partial overlap between the MIPs proved useful for advancing the understanding of the perturbation-response paradigm through multi-model ensembles of Earth system models of varying complexity. We discuss the challenges of gaining insights from Earth system models that face computational and process representation limits and provide guidance from our lessons learned. Promising i
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Journal articleFeingold G, Ghate VP, Russell LM, et al., 2024,
Physical science research needed to evaluate the viability and risks of marine cloud brightening.
, Sci Adv, Vol: 10Marine cloud brightening (MCB) is the deliberate injection of aerosol particles into shallow marine clouds to increase their reflection of solar radiation and reduce the amount of energy absorbed by the climate system. From the physical science perspective, the consensus of a broad international group of scientists is that the viability of MCB will ultimately depend on whether observations and models can robustly assess the scale-up of local-to-global brightening in today's climate and identify strategies that will ensure an equitable geographical distribution of the benefits and risks associated with projected regional changes in temperature and precipitation. To address the physical science knowledge gaps required to assess the societal implications of MCB, we propose a substantial and targeted program of research-field and laboratory experiments, monitoring, and numerical modeling across a range of scales.
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Journal articleKuhlbrodt T, Swaminathan R, Ceppi P, et al., 2024,
A Glimpse into the Future The 2023 Ocean Temperature and Sea Ice Extremes in the Context of Longer-Term Climate Change
, Bulletin of the American Meteorological Society, Vol: 105, Pages: E474-E485, ISSN: 0003-0007In the year 2023, we have seen extraordinary extrema in high sea surface temperature (SST) in the North Atlantic and in low sea ice extent in the Southern Ocean, outside the 4σ envelope of the 1982–2011 daily time series. Earth’s net global energy imbalance (12 months up to September 2023) amounts to +1.9 W m−2 as part of a remarkably large upward trend, ensuring further heating of the ocean. However, the regional radiation budget over the North Atlantic does not show signs of a suggested significant step increase from less negative aerosol forcing since 2020. While the temperature in the top 100 m of the global ocean has been rising in all basins since about 1980, specifically the Atlantic basin has continued to further heat up since 2016, potentially contributing to the extreme SST. Similarly, salinity in the top 100 m of the ocean has increased in recent years specifically in the Atlantic basin, and in addition in about 2015 a substantial negative trend for sea ice extent in the Southern Ocean began. Analyzing climate and Earth system model simulations of the future, we find that the extreme SST in the North Atlantic and the extreme in Southern Ocean sea ice extent in 2023 lie at the fringe of the expected mean climate change for a global surface-air temperature warming level (GWL) of 1.5°C, and closer to the average at a 3.0°C GWL. Understanding the regional and global drivers of these extremes is indispensable for assessing frequency and impacts of similar events in the coming years.
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Journal articleKellogg PJ, Mozer FS, Moncuquet M, et al., 2024,
Heating and Acceleration of the Solar Wind by Ion Acoustic Waves—Parker Solar Probe
, Astrophysical Journal, Vol: 964, ISSN: 0004-637XThe heating of the solar wind has been shown to be correlated with certain ion acoustic waves. Here calculations of the heating are made, using the methods used previously for STEREO observations, which show that the strong damping of ion acoustic waves rapidly delivers their energy to the plasma of the solar wind. It is shown that heating by the observed waves is not only sufficient to produce the observed heating but can also provide much or all of the outward acceleration of the solar wind.
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Journal articleJohnson M, Rivera YJ, Niembro T, et al., 2024,
Helium Abundance Periods Observed by the Solar Probe Cup on Parker Solar Probe: Encounters 1-14
, Astrophysical Journal, Vol: 964, ISSN: 0004-637XParker Solar Probe is a mission designed to explore the properties of the solar wind closer than ever before. Detailed particle observations from the Solar Probe Cup (SPC) have primarily focused on examining the proton population in the solar wind. However, several periods throughout the Parker mission have indicated that SPC has observed a pronounced and distinctive population of fully ionized helium, He2+. Minor ions are imprinted with properties of the solar wind’s source region, as well as mechanisms active during outflow, making them sensitive markers of its origin and formation at the Sun. Through a detailed analysis of the He2+ velocity distributions functions, this work examines periods where significant and persistent He2+ peaks are observed with SPC. We compute the helium abundance and examine the stream’s bulk speed, density, temperature, magnetic field topology, and electron strahl properties to identify distinctive solar-wind features that can provide insight to their solar source. We find that nearly all periods exhibit an elevated mean helium composition (8.34%) compared to typical solar wind and a majority (∼87%) of these periods are connected to coronal mass ejections (CMEs), with the highest abundance reaching 23.1%. The helium abundance and number of events increases as the solar cycle approaches maximum, with a weak dependence on speed. Additionally, the events not associated with a CME are clustered near the heliospheric current sheet, suggesting they are connected to streamer belt outflows. However, there are currently no theoretical explanations that fully describe the range of depleted and elevated helium abundances observed.
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Journal articleRojo M, Persson M, Sauvaud JA, et al., 2024,
Electron moments derived from the Mercury Electron Analyzer during the cruise phase of BepiColombo
, Astronomy and Astrophysics, Vol: 683, ISSN: 0004-6361Aims. We derive electron density and temperature from observations obtained by the Mercury Electron Analyzer on board Mio during the cruise phase of BepiColombo while the spacecraft is in a stacked configuration. Methods. In order to remove the secondary electron emission contribution, we first fit the core electron population of the solar wind with a Maxwellian distribution. We then subtract the resulting distribution from the complete electron spectrum, and suppress the residual count rates observed at low energies. Hence, our corrected count rates consist of the sum of the fitted Maxwellian core electron population with a contribution at higher energies. We finally estimate the electron density and temperature from the corrected count rates using a classical integration method. We illustrate the results of our derivation for two case studies, including the second Venus flyby of BepiColombo when the Solar Orbiter spacecraft was located nearby, and for a statistical study using observations obtained to date for distances to the Sun ranging from 0.3 to 0.9 AU. Results. When compared either to measurements of Solar Orbiter or to measurements obtained by HELIOS and Parker Solar Probe, our method leads to a good estimation of the electron density and temperature. Hence, despite the strong limitations arising from the stacked configuration of BepiColombo during its cruise phase, we illustrate how we can retrieve reasonable estimates for the electron density and temperature for timescales from days down to several seconds.
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