The THEMIS Fluxgate Magnetometer

Auster, H. U.; Glaßmeier, Karl‐Heinz; Magnes, W.; Aydogar, Özer; Baumjohann, W.; Constantinescu, Dragoş; Fischer, D.; Fornaçon, K.‐H.; Georgescu, E.; Harvey, P.; Hillenmaier, O.; Kroth, R.; Ludlam, M.; Narita, Yasuhito; Nakamura, R.; Okrafka, K.; Plaschke, Ferdinand; Richter, Ingo; Schwarzl, H.; Stoll, B.; Valavanoglou, A.; Wiedemann, Martin

doi:10.1007/s11214-008-9365-9

Cited by 1,141 publications

(989 citation statements)

References 17 publications

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“…All five THEMIS probes [Angelopoulos, 2008;Frey et al, 2008] in formation flight with identical instrumentation are used to reveal the latitudinal profile of the current sheet. The magnetic field data are from the fluxgate magnetometers on 2 m booms [Auster et al, 2008]. Though their sampling rate is as much as 64 Hz, we use averaged values over 3 s and 5 min.…”

Section: Resultsmentioning

confidence: 99%

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Saito

Fairfield

et al. 2011

J. Geophys. Res.

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[1] THEMIS five-point observations on April 8, 2009 were used to study thinning of the current sheet in the near-Earth tail that led to the onset of a small substorm. Taking advantage of a fortuitous alignment of the five spacecraft near 2300 LT and 11 R E and within 1.5 R E of the current sheet center, latitudinal gradients are analyzed. A significant latitudinal pressure gradient is present indicating the necessity of a (J × B) z force to maintain the pre-onset equilibrium state. During thinning the total pressure remained approximately constant at all spacecraft rather than increasing. Within the plasma sheet, magnetic field strength increased while plasma pressure decreased due to decreasing temperature. We present a comprehensive explanation for the relationship between the thinning, the stretched structure, and development of intense current density. Our analysis of this event suggests that (1) the thinning in this event is an MHD force-balanced self-evolving process and is not a forced process due to an increased lobe field; (2) the thinning changes flux tube structure in length and curvature but not significantly in volume; (3) the thinning evolves with a change of the radial plasma pressure profile in the near-Earth tail, which is associated with a locally intensified current sheet. The conclusion is that the increased lobe field strength is not the necessary and the primary cause for cross tail current sheet thinning but rather thinning can occur within the plasma sheet as a result of unknown internal processes.

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Section: Resultsmentioning

confidence: 99%

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Saito

Fairfield

et al. 2011

J. Geophys. Res.

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“…Figure 6d shows the chorus activity obtained using filter bank data measured by the Search Coil Magnetometer (SCM) [Le Contel et al, 2008] on board the three inner THEMIS probes [Angelopoulos, 2008]. Simultaneous electron cyclotron frequency (fce), inferred from the local background magnetic field measurements from the Flux Gate Magnetometer (FGM) [Auster et al, 2008], is used to select the appropriate frequencies to capture the main power of chorus between 0.1 and 0.8 fce. The inferred chorus activity obtained using POES electron data is shown in Figure 6e.…”

Section: Plasma Wave Observationsmentioning

confidence: 99%

Relativistic electron response to the combined magnetospheric impact of a coronal mass ejection overlapping with a high‐speed stream: Van Allen Probes observations

et al. 2015

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During early November 2013, the magnetosphere experienced concurrent driving by a coronal mass ejection (CME) during an ongoing high‐speed stream (HSS) event. The relativistic electron response to these two kinds of drivers, i.e., HSS and CME, is typically different, with the former often leading to a slower buildup of electrons at larger radial distances, while the latter energizing electrons rapidly with flux enhancements occurring closer to the Earth. We present a detailed analysis of the relativistic electron response including radial profiles of phase space density as observed by both Magnetic Electron and Ion Sensor (MagEIS) and Relativistic Electron Proton Telescope instruments on the Van Allen Probes mission. Data from the MagEIS instrument establish the behavior of lower energy (<1 MeV) electrons which span both intermediary and seed populations during electron energization. Measurements characterizing the plasma waves and magnetospheric electric and magnetic fields during this period are obtained by the Electric and Magnetic Field Instrument Suite and Integrated Science instrument on board Van Allen Probes, Search Coil Magnetometer and Flux Gate Magnetometer instruments on board Time History of Events and Macroscale Interactions during Substorms, and the low‐altitude Polar‐orbiting Operational Environmental Satellites. These observations suggest that during this time period, both radial transport and local in situ processes are involved in the energization of electrons. The energization attributable to radial diffusion is most clearly evident for the lower energy (<1 MeV) electrons, while the effects of in situ energization by interaction of chorus waves are prominent in the higher‐energy electrons.

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“…The apogee of THEMIS A was shifted to ∼12 R E and was against the plasma sheet in the 2009 season. We used the data of the electric field instrument [Bonnell et al, 2008], the fluxgate magnetometer [Auster et al, 2008], the electrostatic analyzer (ESA) [McFadden et al, 2008], and the solid state telescope (SST). These data are given in a 3 s time resolution.…”

Section: Data Setsmentioning

confidence: 99%

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

et al. 2011

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[1] Fast azimuthal auroral expansion and poleward expansion are characteristic features of the expansion phase of substorms. In the first study of its kind, we have investigated the azimuthal auroral expansion and its magnetospheric counterpart using data from Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imagers and multiple spacecraft. During the tail season in 2008-2009, we found 16 events of azimuthally expanding aurora that passed near the magnetic footprints of the multiple spacecraft operating in the near-Earth plasma sheet. In the magnetosphere, these events commonly showed fast azimuthal and earthward flows associated with intense electric fields and magnetic dipolarization. The speed of the propagating structure, which was estimated from the time difference of the depolarization observed by the multiple spacecraft, was close to the measured azimuthal plasma flow velocity. We also found that this azimuthal plasma transport was dominated by the E × B drift speed associated with the enhanced electric field. In a statistical analysis, the averaged speeds of the leading edge of the westward and eastward auroral expansion were 8.8 and 5.3 km/s, respectively. When mapped onto the equatorial magnetosphere, these speeds (267 and 162 km/s) were comparable to the averaged azimuthal plasma (E × B) flow speeds observed by the spacecraft, which were 193 (239) km/s in the westward direction and 112 (139) km/s in the eastward direction. Our events showed that E × B flows and auroral expansion predominantly propagated westward, indicating an effect of westward background convection in the Harang flow shear. From these results, we concluded that the azimuthal auroral expansion was closely related to magnetic dipolarization which expanded azimuthally at the E × B drift speed. On the basis of the abrupt formation of the fast E × B flows and their propagation away from the onset location, we suggest that the effects of the intense large-scale electric fields, which are possibly generated through substorm onset turbulence, propagate to the ionosphere along the magnetic field lines and lead to azimuthal expansion of an auroral arc.

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The THEMIS Fluxgate Magnetometer

Cited by 1,141 publications

References 17 publications

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Relativistic electron response to the combined magnetospheric impact of a coronal mass ejection overlapping with a high‐speed stream: Van Allen Probes observations

Azimuthal auroral expansion associated with fast flows in the near-Earth plasma sheet: Coordinated observations of the THEMIS all-sky imagers and multiple spacecraft

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