| 1. |
- Dimmock, Andrew P., et al.
(author)
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Direct evidence of nonstationary collisionless shocks in space plasmas
- 2019
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In: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 5:2
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Journal article (peer-reviewed)abstract
- Collisionless shocks are ubiquitous throughout the universe: around stars, supernova remnants, active galactic nuclei, binary systems, comets, and planets. Key information is carried by electromagnetic emissions from particles accelerated by high Mach number collisionless shocks. These shocks are intrinsically nonstationary, and the characteristic physical scales responsible for particle acceleration remain unknown. Quantifying these scales is crucial, as it affects the fundamental process of redistributing upstream plasma kinetic energy into other degrees of freedom-particularly electron thermalization. Direct in situ measurements of nonstationary shock dynamics have not been reported. Thus, the model that best describes this process has remained unknown. Here, we present direct evidence demonstrating that the transition to nonstationarity is associated with electron-scale field structures inside the shock ramp.
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| 2. |
- Krasnoselskikh, Vladimir, et al.
(author)
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ICARUS : in-situ studies of the solar corona beyond Parker Solar Probe and Solar Orbiter
- 2022
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In: Experimental astronomy. - : Springer Nature. - 0922-6435 .- 1572-9508. ; 54:2-3, s. 277-315
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Journal article (peer-reviewed)abstract
- The primary scientific goal of ICARUS (Investigation of Coronal AcceleRation and heating of solar wind Up to the Sun), a mother-daughter satellite mission, proposed in response to the ESA “Voyage 2050” Call, will be to determine how the magnetic field and plasma dynamics in the outer solar atmosphere give rise to the corona, the solar wind, and the entire heliosphere. Reaching this goal will be a Rosetta Stone step, with results that are broadly applicable within the fields of space plasma physics and astrophysics. Within ESA’s Cosmic Vision roadmap, these science goals address Theme 2: “How does the Solar System work?” by investigating basic processes occurring “From the Sun to the edge of the Solar System”. ICARUS will not only advance our understanding of the plasma environment around our Sun, but also of the numerous magnetically active stars with hot plasma coronae. ICARUS I will perform the first direct in situ measurements of electromagnetic fields, particle acceleration, wave activity, energy distribution, and flows directly in the regions in which the solar wind emerges from the coronal plasma. ICARUS I will have a perihelion altitude of 1 solar radius and will cross the region where the major energy deposition occurs. The polar orbit of ICARUS I will enable crossing the regions where both the fast and slow winds are generated. It will probe the local characteristics of the plasma and provide unique information about the physical processes involved in the creation of the solar wind. ICARUS II will observe this region using remote-sensing instruments, providing simultaneous, contextual information about regions crossed by ICARUS I and the solar atmosphere below as observed by solar telescopes. It will thus provide bridges for understanding the magnetic links between the heliosphere and the solar atmosphere. Such information is crucial to our understanding of the plasma physics and electrodynamics of the solar atmosphere. ICARUS II will also play a very important relay role, enabling the radio-link with ICARUS I. It will receive, collect, and store information transmitted from ICARUS I during its closest approach to the Sun. It will also perform preliminary data processing before transmitting it to Earth. Performing such unique in situ observations in the area where presumably hazardous solar energetic particles are energized, ICARUS will provide fundamental advances in our capabilities to monitor and forecast the space radiation environment. Therefore, the results from the ICARUS mission will be extremely crucial for future space explorations, especially for long-term crewed space missions.
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| 3. |
- Liemohn, Michael W., et al.
(author)
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Model Evaluation Guidelines for Geomagnetic Index Predictions
- 2018
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In: Space Weather. - 1542-7390. ; 16:12, s. 2079-2102
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Journal article (peer-reviewed)abstract
- Geomagnetic indices are convenient quantities that distill the complicated physics of some region or aspect of near‐Earth space into a single parameter. Most of the best‐known indices are calculated from ground‐based magnetometer data sets, such as Dst, SYM‐H, Kp, AE, AL, and PC. Many models have been created that predict the values of these indices, often using solar wind measurements upstream from Earth as the input variables to the calculation. This document reviews the current state of models that predict geomagnetic indices and the methods used to assess their ability to reproduce the target index time series. These existing methods are synthesized into a baseline collection of metrics for benchmarking a new or updated geomagnetic index prediction model. These methods fall into two categories: (1) fit performance metrics such as root‐mean‐square error and mean absolute error that are applied to a time series comparison of model output and observations and (2) event detection performance metrics such as Heidke Skill Score and probability of detection that are derived from a contingency table that compares model and observation values exceeding (or not) a threshold value. A few examples of codes being used with this set of metrics are presented, and other aspects of metrics assessment best practices, limitations, and uncertainties are discussed, including several caveats to consider when using geomagnetic indices.
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| 4. |
- Agapitov, Oleksiy, et al.
(author)
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Statistics of whistler mode waves in the outer radiation belt : Cluster STAFF-SA measurements
- 2013
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In: Journal of Geophysical Research-Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 118:6, s. 3407-3420
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Journal article (peer-reviewed)abstract
- ELF/VLF waves play a crucial role in the dynamics of the radiation belts and are partly responsible for the main losses and the acceleration of energetic electrons. Modeling wave-particle interactions requires detailed information of wave amplitudes and wave normal distribution over L-shells and over magnetic latitudes for different geomagnetic activity conditions. We performed a statistical study of ELF/VLF emissions using wave measurements in the whistler frequency range for 10years (2001-2010) aboard Cluster spacecraft. We utilized data from the STAFF-SA experiment, which spans the frequency range from 8Hz to 4kHz. We present distributions of wave magnetic and electric field amplitudes and wave normal directions as functions of magnetic latitude, magnetic local time, L-shell, and geomagnetic activity. We show that wave normals are directed approximately along the background magnetic field (with the mean value of the angle between the wave normal and the background magnetic field, about 10 degrees-15 degrees) in the vicinity of the geomagnetic equator. The distribution changes with magnetic latitude: Plasmaspheric hiss normal angles increase with latitude to quasi-perpendicular direction at approximate to 35 degrees-40 degrees where hiss can be reflected; lower band chorus are observed as two wave populations: One population of wave normals tends toward the resonance cone and at latitudes of around 35 degrees-45 degrees wave normals become nearly perpendicular to the magnetic field; the other part remains quasi-parallel at latitudes up to 30 degrees. The observed angular distribution is significantly different from Gaussian, and the width of the distribution increases with latitude. Due to the rapid increase of , the wave mode becomes quasi-electrostatic, and the corresponding electric field increases with latitude and has a maximum near 30 degrees. The magnetic field amplitude of the chorus in the day sector has a minimum at the magnetic equator but increases rapidly with latitude with a local maximum near 12 degrees-15 degrees. The wave magnetic field maximum is observed in the night sector at L>7 during low geomagnetic activity (at L approximate to 5 for K-p>3). Our results confirm the strong dependence of wave amplitude on geomagnetic activity found in earlier studies.
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