A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS)

Lee, S.; Shiokawa, K.; McFadden, J. P.; Nishimura, Y.

doi:10.1029/2011ja016954

Cited by 7 publications

(7 citation statements)

References 42 publications

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“… S. Lee et al [2011]showed that the average density of the ‘thermal’ FAC (i.e., FAC without field‐aligned acceleration) during a quiet time ( AE < 100 nT) is of the order of 0.1 μ A/m 2 at 9–12 R E (near‐Earth tail), where R E is the Earth's radius. It was also shown that the thermal FAC density decreases with tailward distance from the Earth [ S. Lee et al , 2011, p. 8]. As the dayside segment of our polar arc (Figure 4) is probably mapped to the LLBL, the expected thermal FAC density is ≤0.1 μ A/m 2 .…”

Section: Discussionmentioning

confidence: 99%

Dayside and nightside segments of a polar arc: The particle characteristics

et al. 2012

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[1] Using multiple satellites and a ground-based radar network, the physical characteristics of a polar arc and its evolution are investigated under quiet solar wind conditions. The average electron energy is higher at the near-midnight segment than at the sunward extension of the polar arc. Both polar arc segments are positioned primarily on closed magnetic field lines. The convection reversal boundary in the fitted convection pattern was located close to the transition region in the average electron energy seen by the satellites. The topside plasma density at an altitude of 680 km is clearly enhanced around the polar arc, although the enhancement boundary does not coincide precisely with that of the precipitation. The temporal sequence of auroral images suggests that the polar arcs emerged from a double oval structure. This suggestion is supported by the observed physical characteristics of the polar arc, which are quite similar to those of double oval structures that have been reported previously.

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Section: Discussionmentioning

confidence: 99%

Dayside and nightside segments of a polar arc: The particle characteristics

et al. 2012

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“…Longer duration, better instrumented, and/or multispacecraft LEO missions were characteristic of the post‐2000 time frame. Data from these missions provided the basis for more sophisticated models that link Earth's upper atmosphere to geospace: Astrid [ Marklund et al ., ]; Ørsted [ Stauning et al ., ; Christiansen et al ., ; Vennerstrøm et al ., ]; SAC‐C [ Staunin g, ]; FAST [ Strangeway et al ., ; Cattell et al ., ]; FAST and THEMIS [ Lee et al ., ]; CLUSTER [ Dunlop et al ., ]; CHAMP [ Watermann et al ., ; Wang et al ., ; Juusola et al ., ; He et al ., ]; ST‐5 [ Wang et al ., ; Gjerloev et al ., ]; and Block 5‐D3 DMSP spacecraft [ Huang and Burke , ; Ohtani et al ., ; Rich et al ., ; Nakano et al ., ; Wing et al ., , ]. This partial listing of FAC‐related articles clearly shows that in less than five decades, understanding of FACs evolved from statistics gleaned from individual satellite passes, and ensembles of these data, to time‐integrated global perspectives provided by satellite constellations.…”

Section: Background and Motivationmentioning

confidence: 98%

Comparison of magnetic perturbation data from LEO satellite constellations: Statistics of DMSP and AMPERE

et al. 2014

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During the past decade engineering-grade magnetic field measurements from the low Earth orbiting (LEO) Iridium constellation of communication satellites have been available to the geospace science community as a tool to map field-aligned currents. The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) applied to Iridium measurements markedly improved the temporal and spatial resolution of these data. We developed new methods to compare data from the latest improvement to AMPERE with those from a constellation of four LEO Defense Meteorological Satellite Program (DMSP) spacecraft that carry high-resolution magnetometers. To perform the comparisons, we transformed all data to a common coordinate frame and altitude (110 km) and developed a means of computing spacecraft magnetic conjunctions. These conjunctions yield discrepancies in the magnetic field perturbations measured at each proximate spacecraft. During the geomagnetic disturbance of 29-30 May 2010, the vector differences in the horizontal perturbations at closest approach (typically a few tens of kilometers) had mean, median, and standard deviation values of 132 nT, 112 nT, and 90 nT, respectively. The DMSP spacecraft tend to report larger perturbations in the northern polar cap and cusp regions, especially during active intervals. We attribute some of the differences to limitations of spacecraft-attitude knowledge that propagate into AMPERE data. Overall, for the magnetic storm, we provide clear evidence that AMPERE data can provide high-resolution auroral zone data in good agreement with DMSP data for use in data assimilation algorithms. Such dual-use commercial data can provide important global augmentation to the nation's space weather monitoring capabilities. Background and MotivationEarth's thermosphere, where most low Earth orbiting (LEO) satellites operate, is subject to a variety of space weather disturbances. As first discussed in Cummings and Dessler [1967], many of these disturbances are closely linked to variations in magnetic field-aligned currents (FAC), which are often referred to as Birkeland currents. Although hundreds of satellites have operated in LEO, until this millennium only about a dozen had been equipped with high-quality vector magnetometers needed for characterizing FAC behavior. From the 1970's to the turn of the century, direct knowledge of FAC structure and behavior was ascertained from individual or sequential passes of LEO (or LEO-approach) missions that included the following: Satellite 1963-38C [Zmuda et al

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“…Precipitating electrons carrying the upward FAC portion of this current system would explain the measured poleward propagation. The reason for being diffuse rather than discrete aurora is because the density at low L ‐shells is generally high enough to carry FACs without requiring parallel potential drop (Lee et al, ). It is also noted that these two diffuse aurora brightenings were both followed by dimmings compared to auroral intensity during the pre‐HSJ interval, which were consistent with decreases of the x component of the dynamic pressure after the HSJs.…”

Section: Case Studymentioning

confidence: 99%

Impacts of Magnetosheath High‐Speed Jets on the Magnetosphere and Ionosphere Measured by Optical Imaging and Satellite Observations

et al. 2018

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Magnetosheath high-speed jets (HSJs) are dayside upstream transient disturbances with enhanced flow velocity and dynamic pressure. They are associated with significant magnetopause perturbations, ultralow frequency waves in the dayside magnetosphere, and localized flow enhancements in the ionosphere. However, whether HSJs have corresponding dayside aurora signatures is still an open question. If auroral signatures are found, 2-D structure and evolution of HSJ effects on the magnetosphere can be imaged in a much higher precision than possible by other means. In this study, eight HSJ events are identified by the THEMIS satellites located within ±1 MLT of the center of the field-of-view of the South Pole station all-sky imager. In all of those cases, the HSJs are observed to have a nearly one-to-one relationship with individual localized discrete/diffuse auroral brightenings. The azimuthal size of HSJ-related diffuse aurora signatures is~800 km at 230-km altitude in the ionosphere and~3.7 Re in the magnetosphere, which is slightly larger but of the order of the cross-sectional diameter of HSJs (~1 Re). Furthermore, most of those aurora signatures have azimuthal motion, whose magnitude and direction agree with magnetosheath background flows. This study for the first time shows high-resolution, two-dimensional observations of localized structure and fast propagation of precipitation due to magnetosheath HSJs. We conclude that magnetosheath HSJs can have substantial impacts on the coupled magnetosphere-ionosphere system, causing localized magnetospheric compression and aurora brightening, in a similar manner to responses during interplanetary shocks except with a smaller scale size. Recent papers show that HSJs tend to occur when the IMF cone angle is low, especially less than 40°( Plaschke et al., 2013). Hietala et al. (2009) suggested that HSJs are probably generated due to the ripples of the quasi-parallel bow shock, and a quantitative study shows that 97% of the observed HSJs can be

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A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS)

Cited by 7 publications

References 42 publications

Dayside and nightside segments of a polar arc: The particle characteristics

Dayside and nightside segments of a polar arc: The particle characteristics

Comparison of magnetic perturbation data from LEO satellite constellations: Statistics of DMSP and AMPERE

Impacts of Magnetosheath High‐Speed Jets on the Magnetosphere and Ionosphere Measured by Optical Imaging and Satellite Observations

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