1. |
- Aad, G, et al.
(author)
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Searches for scalar leptoquarks in pp collisions at [Formula: see text] = 8 TeV with the ATLAS detector.
- 2016
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
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Journal article (peer-reviewed)abstract
- Searches for pair-produced scalar leptoquarks are performed using 20 fb[Formula: see text] of proton-proton collision data provided by the LHC and recorded by the ATLAS detector at [Formula: see text] TeV. Events with two electrons (muons) and two or more jets in the final state are used to search for first (second)-generation leptoquarks. The results from two previously published ATLAS analyses are interpreted in terms of third-generation leptoquarks decaying to [Formula: see text] and [Formula: see text] final states. No statistically significant excess above the Standard Model expectation is observed in any channel and scalar leptoquarks are excluded at 95 % CL with masses up to [Formula: see text] 1050 GeV for first-generation leptoquarks, [Formula: see text] 1000 GeV for second-generation leptoquarks, [Formula: see text] 625 GeV for third-generation leptoquarks in the [Formula: see text] channel, and 200 [Formula: see text] 640 GeV in the [Formula: see text] channel.
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2. |
- Aad, G, et al.
(author)
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Measurements of fiducial cross-sections for [Formula: see text] production with one or two additional b-jets in pp collisions at [Formula: see text]=8 TeV using the ATLAS detector.
- 2016
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76
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Journal article (peer-reviewed)abstract
- Fiducial cross-sections for [Formula: see text] production with one or two additional b-jets are reported, using an integrated luminosity of 20.3 fb[Formula: see text] of proton-proton collisions at a centre-of-mass energy of 8 TeV at the Large Hadron Collider, collected with the ATLAS detector. The cross-section times branching ratio for [Formula: see text] events with at least one additional b-jet is measured to be 950 [Formula: see text] 70 (stat.) [Formula: see text] (syst.) fb in the lepton-plus-jets channel and 50 [Formula: see text] 10 (stat.) [Formula: see text] (syst.) fb in the [Formula: see text] channel. The cross-section times branching ratio for events with at least two additional b-jets is measured to be 19.3 [Formula: see text] 3.5 (stat.) [Formula: see text] 5.7 (syst.) fb in the dilepton channel ([Formula: see text], [Formula: see text], and ee) using a method based on tight selection criteria, and 13.5 [Formula: see text] 3.3 (stat.) [Formula: see text] 3.6 (syst.) fb using a looser selection that allows the background normalisation to be extracted from data. The latter method also measures a value of 1.30 [Formula: see text] 0.33 (stat.) [Formula: see text] 0.28 (syst.)% for the ratio of [Formula: see text] production with two additional b-jets to [Formula: see text] production with any two additional jets. All measurements are in good agreement with recent theory predictions.
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3. |
- Aad, G., et al.
(author)
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- 2015
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In: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; :12
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Journal article (peer-reviewed)
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4. |
- Aad, G., et al.
(author)
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- 2016
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In: Physical Review D. Particles and fields. - : American Physical Society. - 0556-2821 .- 1089-4918. ; 93:1
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Journal article (peer-reviewed)
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7. |
- Aad, G., et al.
(author)
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- 2016
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In: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; :1
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Journal article (peer-reviewed)
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8. |
- Aad, G., et al.
(author)
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- 2015
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In: Physical Review D. Particles and fields. - : American Physical Society. - 0556-2821 .- 1089-4918. ; 92:9
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Journal article (peer-reviewed)
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9. |
- Aad, G., et al.
(author)
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- 2015
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In: Physical Review D. Particles and fields. - : American Physics Society. - 0556-2821 .- 1089-4918. ; 92:11
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Journal article (peer-reviewed)
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11. |
- Aad, G., et al.
(author)
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- 2015
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In: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; :11
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Journal article (peer-reviewed)
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16. |
- Nannya, Y, et al.
(author)
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Postazacitidine clone size predicts long-term outcome of patients with myelodysplastic syndromes and related myeloid neoplasms
- 2023
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In: Blood advances. - : American Society of Hematology. - 2473-9537 .- 2473-9529. ; 7:14, s. 3624-3636
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Journal article (peer-reviewed)abstract
- Azacitidine is a mainstay of therapy for MDS-related diseases. The purpose of our study is to elucidate the effect of gene mutations on hematological response and overall survival (OS), particularly focusing on their post-treatment clone size. We enrolled a total of 449 patients with MDS or related myeloid neoplasms. They were analyzed for gene mutations in pre- (n=449) and post- (n=289) treatment bone marrow samples using targeted-capture sequencing to assess the impact of gene mutations and their post-treatment clone size on treatment outcomes. In Cox proportional hazard modeling, multi-hit TP53 mutation (HR, 2.03; 95% CI, 1.42-2.91; P<.001), EZH2 mutation (HR, 1.71; 95% CI, 1.14-2.54; P=.009), and DDX41 mutations (HR, 0.33; 95% CI, 0.17-0.62; P<.001), together with age, high-risk karyotypes, low platelet, and high blast counts, independently predicted OS. Post-treatment clone size accounting for all drivers significantly correlated with International Working Group (IWG)-response (P<.001, trend test), except for that of DDX41-mutated clones, which did not predict IWG-response. Combined, IWG-response and post-treatment clone size further improved the prediction of the original model and even that of a recently proposed molecular prediction model, IPSS-M (c-index, 0.653 vs 0.688; P<.001, likelihood ratio test). In conclusion, evaluation of post-treatment clone size, together with pre-treatment mutational profile as well as IWG-response have a role in better prognostication of azacitidine-treated myelodysplasia patients.
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23. |
- Badman, S. V., et al.
(author)
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Rotational modulation and local time dependence of Saturn's infrared H-3(+) auroral intensity
- 2012
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In: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 117
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Journal article (peer-reviewed)abstract
- Planetary auroral emissions reveal the configuration of magnetospheric field-aligned current systems. In this study, Cassini Visual and Infrared Mapping Spectrometer (VIMS) observations of Saturn's pre-equinox infrared H-3(+) aurorae were analysed to show (a) rotational modulation of the auroral intensity in both hemispheres and (b) a significant local time dependence of the emitted intensity. The emission intensity is modulated by the 'planetary period' rotation of auroral current systems in each hemisphere. The northern auroral intensity also displays a lesser anti-phase dependence on the southern rotating current system, indicating that part of the southern current system closes in the northern hemisphere. The southern hemisphere aurorae were most intense in the post-dawn sector, in agreement with some past measurements of auroral field-aligned currents, UV aurora and SKR emitted power. A corresponding investigation of the northern hemisphere auroral intensity reveals a broader dawn-noon enhancement, possibly due to the interaction of the southern rotating current system with that of the north. The auroral intensity was reduced around dusk and post-midnight in both hemispheres. These observations can be explained by the interaction of a rotating field-aligned current system in each hemisphere with one fixed in local time, which is related to the solar wind interaction with magnetospheric field lines.
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30. |
- Miyoshi, Y., et al.
(author)
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The energization and radiation in geospace (ERG) project
- 2012
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In: Dynamics of The Earth's Radiation Belts and Inner Magnetosphere. - : American Geophysical Union (AGU). - 9780875904894 ; , s. 103-116
-
Conference paper (peer-reviewed)abstract
- The Energization and Radiation in Geospace (ERG) project for solar cycle 24 will explore how relativistic electrons in the radiation belts are generated during space storms. This geospace exploration project consists of three research teams: the ERG satellite observation team, the ground-based network observation team, and the integrated data analysis/simulation team. Satellite observation will provide in situ measurements of features such as the plasma distribution function, electric and magnetic fields, and plasma waves, whereas remote sensing by ground-based observations using, for example, HF radars, magnetometers, optical instruments, and radio wave receivers will provide the global state of the geospace. Various kinds of data will be integrated and compared with numerical simulations for quantitative understanding. Such a synergetic approach is essential for comprehensive understanding of relativistic electron generation/loss processes through crossenergy and cross-regional coupling in which different plasma populations and regions are dynamically coupled with each other. In addition, the ERG satellite will utilize a new and innovative measurement technique for wave-particle interactions that can directly measure the energy exchange process between particles and plasma waves. In this paper, we briefly review some of the profound problems regarding relativistic electron accelerations and losses that will be solved by the ERG project, and we provide an overview of the project.
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31. |
- Oimatsu, S., et al.
(author)
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Drift-Bounce Resonance Between Pc5 Pulsations and Ions at Multiple Energies in the Nightside Magnetosphere : Arase and MMS Observations
- 2018
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:15, s. 7277-7286
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Journal article (peer-reviewed)abstract
- A Pc5 wave is observed by the Exploration of energization and Radiation in Geospace Arase satellite in the inner magnetosphere (L similar to 5.4-6.1) near postmidnight (L-magnetic local time similar to 1.8-2.5 hr) during the storm recovery phase on 27 March 2017. Its azimuthal wave number (m-number) is estimated using two independent methods with satellites and ground observations to be -8 to -15. The direct measurement of the m-number enables us to calculate the resonance energy. The flux oscillations of H+ and O+ ions at >= 56.3 keV are caused by drift resonance and those of O+ ions at <= 18.6 keV by bounce resonance. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. The enhancement of the O+/H+ flux ratio at <= 18.6 keV indicates selective acceleration of O+ ions through bounce resonance. Plain Language Summary Geomagnetic pulsations are magnetic fluctuations excited by solar wind or plasma instabilities in the magnetosphere. Pc5 waves are continuous geomagnetic pulsations with a period of 150-600 s. A Pc5 wave was observed in the inner magnetosphere during a magnetic storm on 27 March 2017. It propagated westward with a wave number of 8 to 15 and resonated with charged particles, resulting in oscillations of the H+ and O+ ion fluxes at >= 56.3 keV and the O+ ion fluxes at <= 18.6 keV. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. At the same time, the O+/H+ flux ratio at <= 18.6 keV enhanced corresponding to the O+ ion flux oscillations, which indicates selective acceleration of O+ ions through resonances.
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32. |
- Sekiguchi, M, et al.
(author)
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Integrated multiomics analysis of hepatoblastoma unravels its heterogeneity and provides novel druggable targets
- 2020
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In: NPJ precision oncology. - : Springer Science and Business Media LLC. - 2397-768X. ; 4:1, s. 20-
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Journal article (peer-reviewed)abstract
- Although hepatoblastoma is the most common pediatric liver cancer, its genetic heterogeneity and therapeutic targets are not well elucidated. Therefore, we conducted a multiomics analysis, including mutatome, DNA methylome, and transcriptome analyses, of 59 hepatoblastoma samples. Based on DNA methylation patterns, hepatoblastoma was classified into three clusters exhibiting remarkable correlation with clinical, histological, and genetic features. Cluster F was largely composed of cases with fetal histology and good outcomes, whereas clusters E1 and E2 corresponded primarily to embryonal/combined histology and poor outcomes. E1 and E2, albeit distinguishable by different patient age distributions, were genetically characterized by hypermethylation of the HNF4A/CEBPA-binding regions, fetal liver-like expression patterns, upregulation of the cell cycle pathway, and overexpression of NQO1 and ODC1. Inhibition of NQO1 and ODC1 in hepatoblastoma cells induced chemosensitization and growth suppression, respectively. Our results provide a comprehensive description of the molecular basis of hepatoblastoma and rational therapeutic strategies for high-risk cases.
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34. |
- Goetz, C., et al.
(author)
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Cometary plasma science : Open science questions for future space missions
- 2021
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In: Experimental astronomy. - : Springer Nature. - 0922-6435 .- 1572-9508.
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Journal article (peer-reviewed)abstract
- Comets hold the key to the understanding of our Solar System, its formation and its evolution, and to the fundamental plasma processes at work both in it and beyond it. A comet nucleus emits gas as it is heated by the sunlight. The gas forms the coma, where it is ionised, becomes a plasma, and eventually interacts with the solar wind. Besides these neutral and ionised gases, the coma also contains dust grains, released from the comet nucleus. As a cometary atmosphere develops when the comet travels through the Solar System, large-scale structures, such as the plasma boundaries, develop and disappear, while at planets such large-scale structures are only accessible in their fully grown, quasi-steady state. In situ measurements at comets enable us to learn both how such large-scale structures are formed or reformed and how small-scale processes in the plasma affect the formation and properties of these large scale structures. Furthermore, a comet goes through a wide range of parameter regimes during its life cycle, where either collisional processes, involving neutrals and charged particles, or collisionless processes are at play, and might even compete in complicated transitional regimes. Thus a comet presents a unique opportunity to study this parameter space, from an asteroid-like to a Mars- and Venus-like interaction. The Rosetta mission and previous fast flybys of comets have together made many new discoveries, but the most important breakthroughs in the understanding of cometary plasmas are yet to come. The Comet Interceptor mission will provide a sample of multi-point measurements at a comet, setting the stage for a multi-spacecraft mission to accompany a comet on its journey through the Solar System. This White Paper, submitted in response to the European Space Agency’s Voyage 2050 call, reviews the present-day knowledge of cometary plasmas, discusses the many questions that remain unanswered, and outlines a multi-spacecraft European Space Agency mission to accompany a comet that will answer these questions by combining both multi-spacecraft observations and a rendezvous mission, and at the same time advance our understanding of fundamental plasma physics and its role in planetary systems.
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35. |
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36. |
- Kamio, S., et al.
(author)
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First experiments on plasma production using field-aligned ICRF fast wave antennas in the large helical device
- 2021
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In: Nuclear Fusion. - : Institute of Physics (IOP). - 0029-5515 .- 1741-4326. ; 61:11
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Journal article (peer-reviewed)abstract
- The results of the first experimental series to produce a plasma using the ion cyclotron range of frequency (ICRF) in the large helical device (LHD) within the minority scenario developed at Uragan-2M (U-2M) are presented. The motivation of this study is to provide plasma creation in conditions when an electron cyclotron resonance heating start-up is not possible, and in this way widen the operational frame of helical machines. The major constraint of the experiments is the low RF power to reduce the possibility of arcing. No dangerous voltage increase at the radio-frequency (RF) system elements and no arcing has been detected. As a result, a low plasma density is obtained and the antenna-plasma coupling is not optimal. However, such plasmas are sufficient to be used as targets for further neutral beam injection (NBI) heating. This will open possibilities to explore new regimes of operation at LHD and Wendelstein 7-X (W7-X) stellarator. The successful RF plasma production in LHD in this experimental series stimulates the planning of further studies of ICRF plasma production aimed at increasing plasma density and temperature within the ICRF minority scenario as well as investigating the plasma prolongation by NBI heating.
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37. |
- Bergman, Sofia, et al.
(author)
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Spacecraft potential effects on low-energy ion measurements to be made by probe B1 of Comet Interceptor
- 2024
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In: RAS Techniques and Instruments. - : Oxford University Press (OUP). - 2752-8200. ; 3:1, s. 333-346
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Journal article (peer-reviewed)abstract
- Spacecraft charging causes notorious issues for low-energy plasma measurements. The charged particles are accelerated towards or repelled from the spacecraft surface, affecting both their energy and travel direction. The latter results in a distortion of the effective field of view (FOV) of the instrument making the measurements. The Comet Interceptor mission, planned to be launched in 2029, will make a flyby of a long-period or interstellar comet that ideally is dynamically new. The mission comprises one main spacecraft A, developed by the European Space Agency (ESA), and two sub-probes B1 and B2, developed by the Japan Aerospace Exploration Agency and ESA, respectively. The low-energy plasma measurements made by Comet Interceptor will likely be affected by the spacecraft potential in the case of low relative flyby velocities. On probe B1, the Cometary Ion Mass Spectrometer (CIMS) of the Plasma Suite is an ion mass spectrometer, capable of measuring ions with energies down to 10 eV/q. In this work, we use the Spacecraft Plasma Interaction Software to study the influence of the spacecraft potential on the low-energy ion measurements to be made by CIMS in the inner cometary magnetosphere. The results show that the effective FOV of CIMS is distorted at low energies when the flyby velocity is low. The distortion level is highly geometry dependent, and the largest distortions are caused by the magnetometer boom. Furthermore, the results show that cold ions with bulk velocities in the range 1-10 km s-1, flowing both radially away from and inward towards the nucleus, are detectable by the instrument considering the nominal observation geometry.
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38. |
- De Keyser, J., et al.
(author)
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In situ plasma and neutral gas observation time windows during a comet flyby : Application to the Comet Interceptor mission
- 2024
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In: Planetary and Space Science. - : Elsevier. - 0032-0633 .- 1873-5088. ; 244
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Journal article (peer-reviewed)abstract
- A 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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39. |
- Holland, Linda Z, et al.
(author)
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The amphioxus genome illuminates vertebrate origins and cephalochordate biology
- 2008
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In: Genome Research. - : Cold Spring Harbor Laboratory. - 1088-9051 .- 1549-5469. ; 18:7, s. 1100-1111
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Journal article (peer-reviewed)abstract
- Cephalochordates, urochordates, and vertebrates evolved from a common ancestor over 520 million years ago. To improve our understanding of chordate evolution and the origin of vertebrates, we intensively searched for particular genes, gene families, and conserved noncoding elements in the sequenced genome of the cephalochordate Branchiostoma floridae, commonly called amphioxus or lancelets. Special attention was given to homeobox genes, opsin genes, genes involved in neural crest development, nuclear receptor genes, genes encoding components of the endocrine and immune systems, and conserved cis-regulatory enhancers. The amphioxus genome contains a basic set of chordate genes involved in development and cell signaling, including a fifteenth Hox gene. This set includes many genes that were co-opted in vertebrates for new roles in neural crest development and adaptive immunity. However, where amphioxus has a single gene, vertebrates often have two, three, or four paralogs derived from two whole-genome duplication events. In addition, several transcriptional enhancers are conserved between amphioxus and vertebrates--a very wide phylogenetic distance. In contrast, urochordate genomes have lost many genes, including a diversity of homeobox families and genes involved in steroid hormone function. The amphioxus genome also exhibits derived features, including duplications of opsins and genes proposed to function in innate immunity and endocrine systems. Our results indicate that the amphioxus genome is elemental to an understanding of the biology and evolution of nonchordate deuterostomes, invertebrate chordates, and vertebrates.
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40. |
- Jones, Geraint H., et al.
(author)
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The Comet Interceptor Mission
- 2024
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In: Space Science Reviews. - : Springer Nature. - 0038-6308 .- 1572-9672. ; 220:1
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Journal article (peer-reviewed)abstract
- Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum Δ V capability of 600 ms − 1 . Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.
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41. |
- Kasaba, Y., et al.
(author)
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The Plasma Wave Investigation (PWI) onboard the BepiColombo/MMO : First measurement of electric fields, electromagnetic waves, and radio waves around Mercury
- 2010
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 58:1-2, s. 238-278
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Journal article (peer-reviewed)abstract
- The BepiColombo Mercury Magnetospheric Orbiter (MMO) spacecraft includes the plasma and radio wave observation system called Plasma Wave Investigation (PWI). Since the receivers for electric field, plasma waves, and radio waves are not installed in any of the preceding spacecraft to Mercury, the PWI will provide the first opportunity for conducting in-situ and remote-sensing observations of electric fields, plasma waves, and radio waves in the Hermean magnetosphere and exosphere. These observations are valuable in studying structure, dynamics, and energy exchange processes in the unique magnetosphere of Mercury. They are characterized by the key words of the non-MHD environment and the peculiar interaction between the relatively large planet without ionosphere and the solar wind with high dynamic pressure. The PWI consists of three sets of receivers (EWO, SORBET, and AM(2)P), connected to two sets of electric field sensors (MEFISTO and WPT) and two kinds of magnetic field sensors (LF-SC and DB-SC). The PWI will observe both waveforms and frequency spectra in the frequency range from DC to 10 MHz for the electric field and from 0.3 Hz to 640kHz for the magnetic field. From 2008, we will start the development of the engineering model, which is conceptually consistent with the flight model design. The present paper discusses the significance and objectives of plasma/radio wave observations in the Hermean magnetosphere, and describes the PWI sensors, receivers and their performance as well as the onboard data processing.
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42. |
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43. |
- Matsumoto, H., et al.
(author)
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Plasma/radio wave observations at mercury by the bepicolombo mmo spacecraft
- 2006
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In: Advances in Geosciences. - : World Scientific Publishing Co.. - 9789812707192 - 9789812569837 ; , s. 83-84
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Book chapter (peer-reviewed)abstract
- The BepiColombo Mercury Magnetospheric Orbiter (MMO) spacecraft comprises the plasma and radio wave observation system called PlasmaWave Investigation (PWI). The PWI is designed and developed in collaboration between Japanese and European scientists. Since plasma/radio wave receivers were not installed in the former spacecraft, Mariner 10, which observed the planet Mercury, the PWI onboard the MMO spacecraft will provide the first plasma/radio wave data from Mercury orbit. It will give important information for studies of energy exchange processes in the unique magnetosphere of Mercury characterized by the interaction between the relatively large planet without ionosphere and the solar wind with high dynamic pressure. The PWI consists of three sets of receivers (EWO, SORBET, and AM2P), connected to two sets of electric field sensors (MEFISTO and WPT) and two kinds of magnetic field sensors (LF-SC and DB-SC). The PWI will observe both waveforms and frequency spectra in the frequency range from DC to 10MHz for the electric field.
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44. |
- Oyama, S., et al.
(author)
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An Ephemeral Red Arc Appeared at 68 degrees MLat at a Pseudo Breakup During Geomagnetically Quiet Conditions
- 2020
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In: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:10
-
Journal article (peer-reviewed)abstract
- Various subauroral optical features have been studied by analyzing data collected during periods of geomagnetic disturbances. Most events have been typically found at geomagnetic latitudes of 45-60 degrees. In this study, however, we present a red arc event found at geomagnetic 68 degrees north (L approximate to 7.1) in the Scandinavian sector during a period of geomagnetically quiet conditions within a short intermission between two high-speed solar wind events. The red arc appeared to coincide with a pseudo breakup at geomagnetic 71-72 degrees N and a rapid equatorward expansion of the polar cap. However, the red arc disappeared in approximately 7 min. Simultaneous measurements with the Swarm A/C satellites indicated the appearance of the red arc at the ionospheric trough minimum and a conspicuous enhancement of the electron temperature, suggesting the generation of the arc by heat flux. Since there are meaningful differences in the red arc features from already-known subauroral optical features such as the stable auroral red (SAR) arc, we considered that the red arc is a new phenomenon. We suggest that the ephemeral red arc may represent the moment of SAR arc birth associated with substorm particle injection, which is generally masked by bright dynamic aurorae.
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45. |
- Retino, A., et al.
(author)
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Cluster observations of energetic electrons and electromagnetic fields within a reconnecting thin current sheet in the Earth's magnetotail
- 2008
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:A12
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Journal article (peer-reviewed)abstract
- We study the acceleration of energetic electrons during magnetotail reconnection by using Cluster simultaneous measurements of three-dimensional electron distribution functions, electric and magnetic fields, and waves in a thin current sheet. We present observations of two consecutive current sheet crossings where the flux of electrons 35 127 keV peaks within an interval of tailward flows. The first crossing shows the signatures of a tailward moving flux rope. The observed magnetic field and density indicate that the flux rope was very dynamic, and a comparison with numerical simulation suggests a crossing right after coalescence of smaller flux ropes. The second crossing occurs within the ion diffusion region. The flux of electrons is largest within the flux rope where they are mainly directed perpendicular to the magnetic field. At the magnetic separatrices, the fluxes are smaller, but the energy spectra are harder and electrons are mainly field aligned. Reconnection electric fields E-Y similar to 7 mV/m are observed within the diffusion region, whereas in the flux rope, EY are much smaller. Waves around lower hybrid frequency do not show a clear correlation with energetic electrons. We interpret the field-aligned electrons at the separatrices as directly accelerated by the reconnection electric field in the diffusion region, whereas we interpret the perpendicular electrons as trapped within the flux rope and accelerated by a combination of betatron acceleration with nonadiabatic pitch-angle scattering. Our observations indicate that thin current sheets during dynamic reconnection are important for in situ production of energetic electrons and that simultaneous measurements of electrons and electromagnetic fields within thin sheets are crucial to understand the acceleration mechanisms.
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