The Fast Auroral SnapshoT (FAST) Mission

Carlson, C. W.; Pfaff, R. F.; Watzin, James G.

doi:10.1029/98gl01592

Cited by 276 publications

(203 citation statements)

References 20 publications

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“…The FAST data showed clearly for the first time the existence of upward electron acceleration in a region of downward current below the spacecraft [Carlson et al, 1998]. It is the upward current region of discrete auroral arcs that is of interest in this paper.…”

Section: Introductionmentioning

confidence: 99%

Energy and pitch angle‐dispersed auroral electrons suggesting a time‐variable, inverted‐V potential structure

Arnoldy¹,

Lynch²,

Austin³

et al. 1999

J. Geophys. Res.

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Abstract. High temporal resolution electron detectors aboard the PHAZE II rocket flight have shown that the energy-dispersed, field-aligned bursts (FABs) are time coincident with pitch angle-dispersed electrons having energies at the maximum voltage of the inverted-V potential. This modulation of the energetic inverted-V electrons is superimposed upon an energy-diffused background resulting in a peak-to-valley ratio of -2 for the pitch angle-dispersed electrons. Since the characteristic energy of the FABs, the order of an eV, is considerably less than that of the plasma sheet electrons (the order of a keV) presumably falling through the inverted-V potential to create the discrete aurora, the modulation mechanism has to be independent of the electron temperature. The mechanism must accelerate the cold electrons over a range of energies from the inverted-V energy down to a few tens of eV. It must do this at the same time it is creating a population of hot, pitch angle-dispersed electrons at the inverted-V energy. Both the energy dispersion of the FABs and the pitch angle dispersion of the inverted-V electrons can be used to determine a source height assuming both populations start from the same source region at the same time. These calculations give source heights between 3500 and 5300 km for various events and disagreement between the two methods the order of 20%, which is within the rather substantial error limits of both calculations. A simple mechanism of providing a common start time for both populations of electrons would be a turning on/off of a spatially limited (vertically), inverted-V potential. The energy-dispersed FABs can be reconstructed at rocket altitudes if one assumes that cold electrons are accelerated to an energy determined by how much of the inverted-V potential they fall through when it is turned on. Similarly, the pitch angle-dispersed, inverted-V electrons can be modeled at rocket altitudes if one assumes that the plasma sheet electrons falling through the entire potential drop all start to do so at the same time when the potential is turned on. The FABs seem to fluctuate at either -10 Hz or near 100 Hz. An important constraint of the on/off mechanism is whether cold electrons (1 eV) can fill the inverted-V volume during the off cycle. The maximum vertical height of the 10 kV potential region for the 10 Hz events would be the order of 100 and 10 km for the 100 Hz events. To get 10 kV, these heights require parallel electric fields of 0.1 and 1 V/m respectively for the 10 and 100 Hz events assuming that the filling is along B from below the inverted-V potential. Alternative mechanisms are also discussed in the light of the data presented. IntroductionIt is generally accepted that there is parallel electric field acceleration of auroral electrons occurring at altitudes the order of 1 R E. The FAST spacecraft at altitudes of -4000 km is either below or within an upward directed electric field region responsible for the acceleration of the electrons producing the discrete aurora within the upw...

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Section: Introductionmentioning

confidence: 99%

Energy and pitch angle‐dispersed auroral electrons suggesting a time‐variable, inverted‐V potential structure

Arnoldy¹,

Lynch²,

Austin³

et al. 1999

J. Geophys. Res.

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“…The mid-altitude particle and field data used for this study were obtained from the FAST satellite [Carlson et al, 1998] The downward-directed electron energy flux measured by FAST between 26:06-10 UT is the high-altitude extension of the 6300-nm auroral arc observed at Gillam. The sample energy spectrum in this region is a highly field-aligned, suprathermal electron stream extending to 1 keV.…”

Section: Flr and Electron Accelerationmentioning

confidence: 99%

Discrete auroral arc, electrostatic shock and suprathermal electrons powered by dispersive, anomalously resistive field line resonance

Lotko

Streltsov

Carlson

1998

Geophysical Research Letters

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104

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Abstract. Particle and field data from a 4100-km-altitude satellite pass through a 1.3-mHz field line resonance, identified by ground-based optical, magnetic and radar signatures, are compared with results from a two-fluid MHI)-gyrokinetic simulation, including dispersively and resistively sustained parallel electric fields. It is shown that the resonance powers spatially adjacent up-and down-going suprathermal-electron fluxes, a 10-km-scale auroral arc and an imbedded electrostatic shock. Alfv6n wave dispersion and anomalous plasma resistivity are key elements in the interpretation of the event.

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“…The FAST satellite (Carlson et al, 1998a) was launched in August 21, 1996 into an 83 elliptic orbit with an apogee of 4175 km and a perigee of 350 km. DC electric and magnetic ®eld data as well as the electron data from FAST are used in this study.…”

Section: Instrumentationmentioning

confidence: 99%

Characteristics of a stable arc based on FAST and MIRACLE observations

et al. 2000

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Abstract. A stable evening sector arc is studied using observations from the FAST satellite at 1250 km altitude and the MIRACLE ground-based network, which contains all-sky cameras, coherent radars (STARE), and magnetometers. Both FAST and STARE observe a northward electric ®eld region of about 200 km width and a ®eld magnitude of about 50 mV/m southward of the arc, which is a typical signature for an evening-sector arc. The ®eld-aligned current determined from FAST electron and magnetometer data are in rather good agreement within the arcs. Outside the arcs, the electron data misses the current carriers of the downward FAC probably because it is mainly carried by electrons of smaller energy than the instrument threshold. Studying the westward propagation speed of small undulations associated with the arc using the all-sky cameras gives a velocity of about 2 km/s. This speed is higher than the background ionospheric plasma speed (about 1 km/s), but it agrees rather well with the idea originally proposed by Davis that the undulations re¯ect an E Â B motion in the acceleration region. The ground magnetograms indicate that the main current¯ows slightly south of the arc. Computing the ionospheric conductivity from FAST electron data and using the ground magnetograms to estimate the current yields an ionospheric electric ®eld pattern, in rather good agreement with FAST results.

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The Fast Auroral SnapshoT (FAST) Mission

Cited by 276 publications

References 20 publications

Energy and pitch angle‐dispersed auroral electrons suggesting a time‐variable, inverted‐V potential structure

Energy and pitch angle‐dispersed auroral electrons suggesting a time‐variable, inverted‐V potential structure

Discrete auroral arc, electrostatic shock and suprathermal electrons powered by dispersive, anomalously resistive field line resonance

Characteristics of a stable arc based on FAST and MIRACLE observations

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