The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Tomas Karlsson - One of the best experts on this subject based on the ideXlab platform.
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quiet discrete Auroral Arcs acceleration mechanisms
Space Science Reviews, 2020Co-Authors: Robert L. Lysak, Tomas Karlsson, M Echim, O Marghitu, R Rankin, Yan Song, Takashi WatanabeAbstract:The theory of the acceleration of Auroral particles is reviewed, focusing on developments in the last 15 years. We discuss elementary plasma physics processes leading to acceleration of electrons to energies compatible with emission observed for quiet, discrete Auroral Arcs, defined as Arcs that have time scales of minutes or more and spatial scales ranging from less than 1 km to tens of kilometers. For context, earlier observations are first described briefly. The theoretical fundamentals of Auroral particle acceleration are based on the kinetic theory of plasmas, in particular the development of parallel electric fields. These parallel electric fields can either be distributed along the magnetic field lines, often associated with the mirror geometry of the geomagnetic field, or concentrated into narrow regions of charge separation known as double layers. Observations have indicated that the acceleration process depends on whether the field-aligned currents are directed away from the Earth, toward the Earth, or in mixed regions of currents often associated with the propagation of Alfven waves. Recent observations from the NASA Fast Auroral SnapshoT (FAST) satellite, the ESA satellite constellation Cluster, and the Japanese Reimei satellite have provided new insights into the Auroral acceleration process and have led to further refinements to the theory of Auroral particle acceleration.
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Quiet, Discrete Auroral Arcs—Observations
Space Science Reviews, 2020Co-Authors: Tomas Karlsson, L. Andersson, D. M. Gillies, Kristina A. Lynch, Octav Marghitu, Noora Partamies, Nithin SivadasAbstract:Quiet, discrete Auroral Arcs are an important and fundamental consequence of solar wind-magnetosphere interaction. We summarize the current standing of observations of such Auroral Arcs. We review the basic characteristics of the Arcs, including occurrence in time and space, lifetimes, width and length, as well as brightness, and the energy of the magnetospheric electrons responsible for the optical emission. We briefly discuss the connection between single and multiple discrete Arcs. The acceleration of the magnetospheric electrons by high-altitude electric potential structure is reviewed, together with our current knowledge of these structures. Observations relating to the potential drop, altitude distribution and lifetimes are reviewed, as well as direct evidence for the parallel electric fields of the acceleration structures. The current closure in the ionosphere of the currents carried by the Auroral electrons is discussed together with its impact on the ionosphere and thermosphere. The connection of Auroral Arcs to the magnetosphere and generator regions is briefly touched upon. Finally we discuss how to progress from the current observational status to further our understanding of Auroral Arcs.
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quiet discrete Auroral Arcs observations
Space Science Reviews, 2020Co-Authors: Tomas Karlsson, L. Andersson, D. M. Gillies, Kristina A. Lynch, Octav Marghitu, Noora Partamies, Nithin SivadasAbstract:Quiet, discrete Auroral Arcs are an important and fundamental consequence of solar wind-magnetosphere interaction. We summarize the current standing of observations of such Auroral Arcs. We review the basic characteristics of the Arcs, including occurrence in time and space, lifetimes, width and length, as well as brightness, and the energy of the magnetospheric electrons responsible for the optical emission. We briefly discuss the connection between single and multiple discrete Arcs. The acceleration of the magnetospheric electrons by high-altitude electric potential structure is reviewed, together with our current knowledge of these structures. Observations relating to the potential drop, altitude distribution and lifetimes are reviewed, as well as direct evidence for the parallel electric fields of the acceleration structures. The current closure in the ionosphere of the currents carried by the Auroral electrons is discussed together with its impact on the ionosphere and thermosphere. The connection of Auroral Arcs to the magnetosphere and generator regions is briefly touched upon. Finally we discuss how to progress from the current observational status to further our understanding of Auroral Arcs.
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the acceleration region of stable Auroral Arcs
Chapman Conference on the Relationship Between Auroral Phenomenology and Magnetospheric Processes FEB 27-MAR 04 2011 Fairbanks AK, 2013Co-Authors: Tomas KarlssonAbstract:The acceleration region above stable, discrete Auroral Arcs is reviewed. Substantial observational evidence shows that the acceleration of Auroral electrons associated with these Arcs is achieved by an electric potential structure above the aurora at altitudes of around 0.5-2 R-E. The morphology, internal structure, and lifetime of the predominantly U-shaped potential structure are discussed, based on observations by a number of spacecrafts. The parallel (to the geomagnetic field) electric field component of the potential structure, which accelerates the Auroral electrons, is discussed in terms of relatively recent direct observations. The most important theories for how the parallel electric field is sustained are also described. The altitude distribution predicted from the various theories is compared to observations, and briefly discussed, as well as their relation to each other.
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On electric field patterns associated with night-side discrete Auroral Arcs : A generalization of an Auroral arc classification scheme
2001Co-Authors: Tomas KarlssonAbstract:On electric field patterns associated with night-side discrete Auroral Arcs : A generalization of an Auroral arc classification scheme
Alexander Kozlovsky - One of the best experts on this subject based on the ideXlab platform.
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field aligned currents of postnoon Auroral Arcs
Journal of Geophysical Research, 2009Co-Authors: Alexander Kozlovsky, Tauno Turunen, S MassettiAbstract:[1] On 9 January 2008, postnoon (at about 15–16 magnetic local time [MLT]) poleward moving Auroral Arcs were observed over Svalbard during slightly negative interplanetary magnetic field (IMF) Bz and the IMF By gradually changing from near zero to about −3 nT. The Arcs appeared from the western (dayside) horizon and developed toward the east coming to the postnoon sector. The steerable 32-m antenna of the European Incoherent Scatter (EISCAT) radar was directed at an elevation angle of 45° to the north-west at about 45° to geomagnetic west, allowing for measurement of azimuthal (along east-west) plasma flow in a range of latitudes. On the basis of this radar configuration, a new method has been developed and applied for calculating the field-aligned currents (FACs) in the vicinity of the Arcs. The Arcs were located in the region of the postnoon convection reversal, and the background upward FAC had a density of about 1 μA/m2. The optical Arcs were of the order of 30–40 km wide and coincided with peaks of upward FAC. The return downward FAC and the southward electric field were observed poleward of the Arcs. Equatorward of the Arcs, secondary weaker Arcs were detected so that the postnoon Arcs appear to have a double structure. These features are surprisingly similar to the electric field and current patterns of morning Sun-aligned Arcs. We suggest that the double arc structure can be explained by the nonlinear ionospheric feedback that results in splitting of the elongated magnetospheric plasma structures associated with the Arcs.
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dynamics and electric currents of morningside sun aligned Auroral Arcs
Journal of Geophysical Research, 2007Co-Authors: Alexander Kozlovsky, Hans Nilsson, Anita Aikio, V. Safargaleev, T Turunen, T Sergienko, K KauristieAbstract:[1] On 13 December 2004, morningside Sun-aligned Auroral Arcs were observed at about 8 MLT over Svalbard (around 75 MLAT) during about 1.5 hours after the IMF Bz component had turned to strongly northward (+10 nT). The Arcs appeared periodically (6.7 min) and moved poleward at a velocity of about 700 m/s. The Arcs occurred during substorm recovery and appeared to develop from the area of enhanced luminosity seen in the western (nightside) horizon toward east. The electric fields and currents associated with the Arcs have been calculated from the EISCAT Svalbard radar observations. The Arcs were associated with periodic spatial structures of 270 km in latitudinal width. Each of the 270-km wide structure consists of four specific FAC regions: the upward FAC region 75-km wide containing the optical arc, the return downward FAC region 100-km wide poleward of the arc; and a secondary weaker arc equatorward of the main arc with a pair of FACs similar to the main arc, but narrower in width. The interchange instability with the ionospheric feedback is suggested as a suitable generation mechanism for such kind Arcs.
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on the field aligned currents in the vicinity of prenoon Auroral Arcs
Geophysical Research Letters, 2005Co-Authors: Alexander Kozlovsky, Hans Nilsson, Tima Sergienko, Anita Aikio, V. Safargaleev, Tauno Turunen, Kirsti KauristieAbstract:[1] The EISCAT Svalbard radar (at 75° MLAT) was used to investigate the ionospheric plasma flows along Auroral Arcs in the 7–11 MLT sector with the radar beam directed along the L-shell. In nine cases Auroral Arcs appeared in the immediate vicinity of the radar beam allowing for observations of plasma flow simultaneously at different distances across the arc. In eight cases the Arcs were associated with a plasma flow shear indicating sheets of upward field-aligned current (FAC) over the Arcs. However, in one case the data indicate a downward net current in the region of the arc, with a flow shear and, especially, a downward FAC sheet adjoining the arc on the equatorial side. We suggest that in the downward FAC sheet, the Kelvin-Helmholtz instability can generate a series of Auroral spots forming an arc, if the current sheet is co-located with a plasma boundary inside the magnetosphere.
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On the field‐aligned currents in the vicinity of prenoon Auroral Arcs
Geophysical Research Letters, 2005Co-Authors: Alexander Kozlovsky, Hans Nilsson, Tima Sergienko, Anita Aikio, V. Safargaleev, Tauno Turunen, Kirsti KauristieAbstract:[1] The EISCAT Svalbard radar (at 75° MLAT) was used to investigate the ionospheric plasma flows along Auroral Arcs in the 7–11 MLT sector with the radar beam directed along the L-shell. In nine cases Auroral Arcs appeared in the immediate vicinity of the radar beam allowing for observations of plasma flow simultaneously at different distances across the arc. In eight cases the Arcs were associated with a plasma flow shear indicating sheets of upward field-aligned current (FAC) over the Arcs. However, in one case the data indicate a downward net current in the region of the arc, with a flow shear and, especially, a downward FAC sheet adjoining the arc on the equatorial side. We suggest that in the downward FAC sheet, the Kelvin-Helmholtz instability can generate a series of Auroral spots forming an arc, if the current sheet is co-located with a plasma boundary inside the magnetosphere.
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Radar observations in the vicinity of pre-noon Auroral Arcs
Annales Geophysicae, 2005Co-Authors: Hans Nilsson, Alexander Kozlovsky, T Sergienko, A. KotikovAbstract:A combination of EISCAT incoherent scatter radar measurements, optical and magnetometer data is used to study the plasma in and around pre-noon structured precipitation and Auroral Arcs. Particular attention is paid to regions of comparatively low E-region density observed adjacent to Arcs or structured precipitation in the EISCAT Svalbard radar field-aligned measurements. Comparison between luminosity and incoherent scatter electron density measurements shows that the low-density regions occur primarily due to the absence of diffuse precipitation rather than to a cavity formation process. Two cases of Arcs and low density/luminosity regions are identified. The first is related to a strong Pc5 pulsation event, and the absence of diffuse precipitation is due to a large-scale modulation of the diffuse precipitation. In the second case the equatormost arc is on a shielding boundary and the low-density region coincides with a strong flow region just poleward of this arc. Regions of high electric field and low luminosity and conductance are observed prior to intensification of the structured precipitation in both cases. The ionospheric current is enhanced in the low conductance region, indicating that the strong electric fields do not result solely from ionospheric polarization electric fields, and thus are mainly driven by magnetospheric processes. The average energy of the precipitating electrons in the Arcs and structured precipitation is, according to EISCAT measurements, 500eV and the energy spectra are similar for the pulsation and shielding cases. The average energy is thus significantly less than in the diffuse precipitation region which shows central CPS-like energy spectra. We suggest that the low ionospheric conductance of 0.7S in the low density regions is favorable for the arc formation process. This is in quantitative agreement with recent simulations of the ionospheric feedback instability. Keywords. Magnetospheric physics (Auroral phenomena; Magnetosphere-ionosphere interactions) ? Ionosphere (Plasma convection)
Octav Marghitu - One of the best experts on this subject based on the ideXlab platform.
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Quiet, Discrete Auroral Arcs—Observations
Space Science Reviews, 2020Co-Authors: Tomas Karlsson, L. Andersson, D. M. Gillies, Kristina A. Lynch, Octav Marghitu, Noora Partamies, Nithin SivadasAbstract:Quiet, discrete Auroral Arcs are an important and fundamental consequence of solar wind-magnetosphere interaction. We summarize the current standing of observations of such Auroral Arcs. We review the basic characteristics of the Arcs, including occurrence in time and space, lifetimes, width and length, as well as brightness, and the energy of the magnetospheric electrons responsible for the optical emission. We briefly discuss the connection between single and multiple discrete Arcs. The acceleration of the magnetospheric electrons by high-altitude electric potential structure is reviewed, together with our current knowledge of these structures. Observations relating to the potential drop, altitude distribution and lifetimes are reviewed, as well as direct evidence for the parallel electric fields of the acceleration structures. The current closure in the ionosphere of the currents carried by the Auroral electrons is discussed together with its impact on the ionosphere and thermosphere. The connection of Auroral Arcs to the magnetosphere and generator regions is briefly touched upon. Finally we discuss how to progress from the current observational status to further our understanding of Auroral Arcs.
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quiet discrete Auroral Arcs observations
Space Science Reviews, 2020Co-Authors: Tomas Karlsson, L. Andersson, D. M. Gillies, Kristina A. Lynch, Octav Marghitu, Noora Partamies, Nithin SivadasAbstract:Quiet, discrete Auroral Arcs are an important and fundamental consequence of solar wind-magnetosphere interaction. We summarize the current standing of observations of such Auroral Arcs. We review the basic characteristics of the Arcs, including occurrence in time and space, lifetimes, width and length, as well as brightness, and the energy of the magnetospheric electrons responsible for the optical emission. We briefly discuss the connection between single and multiple discrete Arcs. The acceleration of the magnetospheric electrons by high-altitude electric potential structure is reviewed, together with our current knowledge of these structures. Observations relating to the potential drop, altitude distribution and lifetimes are reviewed, as well as direct evidence for the parallel electric fields of the acceleration structures. The current closure in the ionosphere of the currents carried by the Auroral electrons is discussed together with its impact on the ionosphere and thermosphere. The connection of Auroral Arcs to the magnetosphere and generator regions is briefly touched upon. Finally we discuss how to progress from the current observational status to further our understanding of Auroral Arcs.
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Quiescent Discrete Auroral Arcs: A Review of Magnetospheric Generator Mechanisms
Space Science Reviews, 2019Co-Authors: Joseph E. Borovsky, Octav Marghitu, Joachim Birn, Marius M. Echim, Shigeru Fujita, Robert L. Lysak, David J. Knudsen, Antonius Otto, Tomo-hiko Watanabe, Takashi TanakaAbstract:One of the longstanding questions of space science is: How does the Earth’s magnetosphere generate Auroral Arcs? A related question is: What form of energy is extracted from the magnetosphere to drive Auroral Arcs? Not knowing the answers to these questions hinders our ability to determine the impact of Auroral Arcs on the magnetospheric system. Magnetospheric mechanisms for driving quiescent Auroral Arcs are reviewed. Two types of quiescent Arcs are (1) low-latitude non-Alfvénic (growth-phase) Arcs magnetically connecting to the electron plasma sheet and (2) high-latitude Arcs magnetically connecting near the plasma-sheet boundary layer. The reviews of the magnetospheric generator mechanisms are separated for the two types of quiescent Arcs. The driving of Auroral-arc currents in large-scale computer simulations is examined. Predicted observables in the magnetosphere and in the ionosphere are compiled for the various generator mechanisms.
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Quiescent Discrete Auroral Arcs: A Review of Magnetospheric Generator Mechanisms
Space Science Reviews, 2019Co-Authors: Joseph E. Borovsky, Octav Marghitu, Joachim Birn, Marius M. Echim, Shigeru Fujita, Robert L. Lysak, David J. Knudsen, Antonius Otto, Tomo-hiko Watanabe, Takashi TanakaAbstract:One of the longstanding questions of space science is: How does the Earth’s magnetosphere generate Auroral Arcs? A related question is: What form of energy is extracted from the magnetosphere to drive Auroral Arcs? Not knowing the answers to these questions hinders our ability to determine the impact of Auroral Arcs on the magnetospheric system. Magnetospheric mechanisms for driving quiescent Auroral Arcs are reviewed. Two types of quiescent Arcs are (1) low-latitude non-Alfvenic (growth-phase) Arcs magnetically connecting to the electron plasma sheet and (2) high-latitude Arcs magnetically connecting near the plasma-sheet boundary layer. The reviews of the magnetospheric generator mechanisms are separated for the two types of quiescent Arcs. The driving of Auroral-arc currents in large-scale computer simulations is examined. Predicted observables in the magnetosphere and in the ionosphere are compiled for the various generator mechanisms.
Nithin Sivadas - One of the best experts on this subject based on the ideXlab platform.
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Quiet, Discrete Auroral Arcs—Observations
Space Science Reviews, 2020Co-Authors: Tomas Karlsson, L. Andersson, D. M. Gillies, Kristina A. Lynch, Octav Marghitu, Noora Partamies, Nithin SivadasAbstract:Quiet, discrete Auroral Arcs are an important and fundamental consequence of solar wind-magnetosphere interaction. We summarize the current standing of observations of such Auroral Arcs. We review the basic characteristics of the Arcs, including occurrence in time and space, lifetimes, width and length, as well as brightness, and the energy of the magnetospheric electrons responsible for the optical emission. We briefly discuss the connection between single and multiple discrete Arcs. The acceleration of the magnetospheric electrons by high-altitude electric potential structure is reviewed, together with our current knowledge of these structures. Observations relating to the potential drop, altitude distribution and lifetimes are reviewed, as well as direct evidence for the parallel electric fields of the acceleration structures. The current closure in the ionosphere of the currents carried by the Auroral electrons is discussed together with its impact on the ionosphere and thermosphere. The connection of Auroral Arcs to the magnetosphere and generator regions is briefly touched upon. Finally we discuss how to progress from the current observational status to further our understanding of Auroral Arcs.
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quiet discrete Auroral Arcs observations
Space Science Reviews, 2020Co-Authors: Tomas Karlsson, L. Andersson, D. M. Gillies, Kristina A. Lynch, Octav Marghitu, Noora Partamies, Nithin SivadasAbstract:Quiet, discrete Auroral Arcs are an important and fundamental consequence of solar wind-magnetosphere interaction. We summarize the current standing of observations of such Auroral Arcs. We review the basic characteristics of the Arcs, including occurrence in time and space, lifetimes, width and length, as well as brightness, and the energy of the magnetospheric electrons responsible for the optical emission. We briefly discuss the connection between single and multiple discrete Arcs. The acceleration of the magnetospheric electrons by high-altitude electric potential structure is reviewed, together with our current knowledge of these structures. Observations relating to the potential drop, altitude distribution and lifetimes are reviewed, as well as direct evidence for the parallel electric fields of the acceleration structures. The current closure in the ionosphere of the currents carried by the Auroral electrons is discussed together with its impact on the ionosphere and thermosphere. The connection of Auroral Arcs to the magnetosphere and generator regions is briefly touched upon. Finally we discuss how to progress from the current observational status to further our understanding of Auroral Arcs.
Robert L. Lysak - One of the best experts on this subject based on the ideXlab platform.
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quiet discrete Auroral Arcs acceleration mechanisms
Space Science Reviews, 2020Co-Authors: Robert L. Lysak, Tomas Karlsson, M Echim, O Marghitu, R Rankin, Yan Song, Takashi WatanabeAbstract:The theory of the acceleration of Auroral particles is reviewed, focusing on developments in the last 15 years. We discuss elementary plasma physics processes leading to acceleration of electrons to energies compatible with emission observed for quiet, discrete Auroral Arcs, defined as Arcs that have time scales of minutes or more and spatial scales ranging from less than 1 km to tens of kilometers. For context, earlier observations are first described briefly. The theoretical fundamentals of Auroral particle acceleration are based on the kinetic theory of plasmas, in particular the development of parallel electric fields. These parallel electric fields can either be distributed along the magnetic field lines, often associated with the mirror geometry of the geomagnetic field, or concentrated into narrow regions of charge separation known as double layers. Observations have indicated that the acceleration process depends on whether the field-aligned currents are directed away from the Earth, toward the Earth, or in mixed regions of currents often associated with the propagation of Alfven waves. Recent observations from the NASA Fast Auroral SnapshoT (FAST) satellite, the ESA satellite constellation Cluster, and the Japanese Reimei satellite have provided new insights into the Auroral acceleration process and have led to further refinements to the theory of Auroral particle acceleration.
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Quiescent Discrete Auroral Arcs: A Review of Magnetospheric Generator Mechanisms
Space Science Reviews, 2019Co-Authors: Joseph E. Borovsky, Octav Marghitu, Joachim Birn, Marius M. Echim, Shigeru Fujita, Robert L. Lysak, David J. Knudsen, Antonius Otto, Tomo-hiko Watanabe, Takashi TanakaAbstract:One of the longstanding questions of space science is: How does the Earth’s magnetosphere generate Auroral Arcs? A related question is: What form of energy is extracted from the magnetosphere to drive Auroral Arcs? Not knowing the answers to these questions hinders our ability to determine the impact of Auroral Arcs on the magnetospheric system. Magnetospheric mechanisms for driving quiescent Auroral Arcs are reviewed. Two types of quiescent Arcs are (1) low-latitude non-Alfvénic (growth-phase) Arcs magnetically connecting to the electron plasma sheet and (2) high-latitude Arcs magnetically connecting near the plasma-sheet boundary layer. The reviews of the magnetospheric generator mechanisms are separated for the two types of quiescent Arcs. The driving of Auroral-arc currents in large-scale computer simulations is examined. Predicted observables in the magnetosphere and in the ionosphere are compiled for the various generator mechanisms.
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Quiescent Discrete Auroral Arcs: A Review of Magnetospheric Generator Mechanisms
Space Science Reviews, 2019Co-Authors: Joseph E. Borovsky, Octav Marghitu, Joachim Birn, Marius M. Echim, Shigeru Fujita, Robert L. Lysak, David J. Knudsen, Antonius Otto, Tomo-hiko Watanabe, Takashi TanakaAbstract:One of the longstanding questions of space science is: How does the Earth’s magnetosphere generate Auroral Arcs? A related question is: What form of energy is extracted from the magnetosphere to drive Auroral Arcs? Not knowing the answers to these questions hinders our ability to determine the impact of Auroral Arcs on the magnetospheric system. Magnetospheric mechanisms for driving quiescent Auroral Arcs are reviewed. Two types of quiescent Arcs are (1) low-latitude non-Alfvenic (growth-phase) Arcs magnetically connecting to the electron plasma sheet and (2) high-latitude Arcs magnetically connecting near the plasma-sheet boundary layer. The reviews of the magnetospheric generator mechanisms are separated for the two types of quiescent Arcs. The driving of Auroral-arc currents in large-scale computer simulations is examined. Predicted observables in the magnetosphere and in the ionosphere are compiled for the various generator mechanisms.
