Multiple‐point electron measurements in a nightside auroral arc: Auroral turbulence II particle observations

Lynch, K. A.; Pietrowski, D.; Torbert, R. B.; Ivchenko, Nickolay; Marklund, Göran; Primdahl, F.

doi:10.1029/1999gl900599

Cited by 37 publications

(33 citation statements)

References 7 publications

(3 reference statements)

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“…Chmyrev et al, 1989;Louarn et al, 1994;Wahlund et al, 1994;Seyler et al, 1995), and to be associated with field-aligned electron bursts at suprathermal energies Wahlund et al, 1998;Chaston et al, 1999;Lynch et al, 1999;Ivchenko et al, 1999). This wave activity is also connected with transverse heating of ions and might cause largescale density depletions.…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic waves and bursty electron acceleration: implications from Freja

et al. 2002

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Abstract. Dispersive Alfvén wave activity is identified in four dayside auroral oval events measured by the Freja satellite. The events are characterized by ion injection, bursty electron precipitation below about 1 keV, transverse ion heating and broadband extremely low frequency (ELF) emissions below the lower hybrid cutoff frequency (a few kHz). Largescale density depletions/cavities, as determined by the Langmuir probe measurements, and strong electrostatic emissions are often observed simultaneously. A correlation study has been carried out between the E and B field fluctuations below 64 Hz and 10 Hz, respectively, (the DC instruments upper threshold) and the characteristics of the precipitating electrons. This study revealed that the energisation of electrons is indeed related to the broadband ELF emissions and that the electrostatic component plays a predominant role during very active magnetospheric conditions. Furthermore, the effect of the ELF electromagnetic emissions on the larger scale field-aligned current systems has been investigated, and it is found that such an effect cannot be detected. Instead, the Alfvénic activity creates a local region of field-aligned currents. It is suggested that dispersive Alfvén waves set up these local field-aligned current regions and, in turn, trigger more electrostatic emissions during certain conditions. In these regions, ions are transversely heated, and large-scale density depletions/cavities may be created during especially active periods.

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Section: Introductionmentioning

confidence: 99%

Electromagnetic waves and bursty electron acceleration: implications from Freja

et al. 2002

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“…However, other observations, both from sounding rockets and polar orbiting satellites, show a broadband spectrum of electrons inconsistent with such a model [e.g., Johnstone and Winningham, 1982;Arnoldy et al, 1985;Robinson et al, 1989;McFadden et al, 1986McFadden et al, , 1987McFadden et al, , 1990Clemmons et al, 1994;Lynch et al, 1994Lynch et al, , 1999Knudsen et al, 1998;Semeter et al, 2001]. Various mechanisms have been proposed for such acceleration, including acceleration at the edge of a potential structure [e.g., McFadden et al, 1986;Lotko, 1986] or acceleration due to broadband electrostatic turbulence [e.g., Knudsen et al, 1998].…”

Section: Introductionmentioning

confidence: 99%

Development of parallel electric fields at the plasma sheet boundary layer

Lysak

Song

2011

J. Geophys. Res.

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[1] Many measurements of auroral particles, in particular recent measurements from the FAST satellite, indicate that the auroral electron distribution is often broad in energy and field-aligned in pitch angle. Such electrons are seen in conjunction with strong kinetic Alfvén waves with small perpendicular wavelength, and so the aurora produced by these electrons has been termed the "Alfvénic aurora." The Alfvénic aurora is predominant at the polar cap boundary of the aurora as well as in the auroral arc that brightens during substorm onset. The process of forming parallel electric fields in Alfvén waves has been investigated by means of three-dimensional two-fluid simulations. Waves with small perpendicular wavelengths can be produced by phase mixing when perpendicular gradients are present in the plasma. At lower altitudes, Alfvén waves can interact with the ionospheric Alfvén resonator and phase mix to scales of a few kilometers. At higher altitudes, the electron thermal speed becomes comparable or larger than the Alfvén speed, and parallel electric fields due to the Landau resonance can develop. This has been modeled in the fluid code by an approximation to the plasma dispersion function used in kinetic theory. Phase mixing is most effective when there are strong gradients, such as at the plasma sheet boundary layer. Simulations indicate that these processes can produce parallel electric fields on scales of a few kilometers (in the cold plasma case) to a few tens of kilometers (in the warm plasma case), comparable to the scale sizes of auroral arcs.

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“…In stark contrast to the massive amount of single satellite data only a very limited number of multi-point satellite observations exist (e.g. The Auroral Turbulence II sounding rocket mission, Lynch et al, 1999; the Enstrophy sounding rocket mission, Zheng et al, 2003; and the CLUSTER II mission, Escoubet et al, 2001). However, rocket observations are brief and event based while the calculation and interpretation of currents deduced from Cluster observations is highly complicated by the orbit configuration.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of the terrestrial field-aligned current system

et al. 2011

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Abstract. We present the first ever comprehensive statistical study of the spatiotemporal characteristics of field-aligned currents in the terrestrial magnetosphere-ionosphere system using multi point measurements. We determine how the FAC density, variability and scale size are coupled. The three ST 5 satellites were in a pearls-on-a-string formation making measurements of the magnetic field with variable interspacecraft separations ranging from a few seconds to about 10 min. More than 4700 sets of satellite passes are analyzed using a robust correlation analysis aimed at determining the variability of the FAC system as a function of scale size and satellite spacing. We find significant differences between the FAC characteristics on the dayside and on the nightside in terms of dynamics of the current systems. On the dayside the FAC characteristics are found to be independent of IMF B z and geomagnetic activity while the nightside indicates increased variability during disturbed conditions. The boundary separating highly and poorly correlated FACs can be fitted by a linear line for satellite separations shorter than 60 s (dayside) and 160 s (nightside). We interpret this as the dayside and nightside magnetospheric reconfiguration times respectively. For times exceeding this the FAC characteristics are suggested to be controlled by the solar wind (dayside) and plasma sheet (nightside) dynamics. Finally, the characteristics of FAC system with scale sizes larger than ∼200 km (at ionospheric altitude) appear to be stable and repeatable on time scales of the order of a minute (i.e. comparable to the low-altitude orbiting satellite's traverse time across the auroral belt). In this sense, our results effectively validate the Iijima and Potemra (1978) assumption that on average the large-scale currents with scale sizes of the Region1 and Correspondence to: J. W. Gjerloev (jesper.gjerloev@ift.uib.no) Region2 are quasi-persistently significant in the transport of energy and momentum between the magnetosphere and the ionosphere.

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Multiple‐point electron measurements in a nightside auroral arc: Auroral turbulence II particle observations

Cited by 37 publications

References 7 publications

Electromagnetic waves and bursty electron acceleration: implications from Freja

Electromagnetic waves and bursty electron acceleration: implications from Freja

Development of parallel electric fields at the plasma sheet boundary layer

Characteristics of the terrestrial field-aligned current system

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