Author:
BOROVSKY JOSEPH E.,ELPHIC RICHARD C.,FUNSTEN HERBERT O.,THOMSEN MICHELLE F.
Abstract
The bulk flows and magnetic-field fluctuations of the plasma sheet
are
investigated using single-point measurements from the ISEE-2 Fast Plasma
Experiment and fluxgate magnetometer. Ten several-hour-long intervals of
continuous data (with 3 s and 12 s time resolution) are analysed. The plasma-sheet
flow appears to be strongly ‘turbulent’ (i.e. the flow is
dominated by
fluctuations that are unpredictable, with rms velocities[Gt ]mean velocities
and
with field fluctuations≈mean fields). The flow velocities are typically
sub-Alfvénic. The flow-velocity probability distribution
P(v) is constructed, and is
found to be well fitted by exponential functions. Autocorrelation functions
[Ascr ](τ) are constructed, and the autocorrelation times τcorr
for the flow velocities
are found to be about 2 min. From the flow measurements, an estimate of
the
mixing length in the plasma sheet is produced, yielding
Lmix≈2 Earth radii;
correspondingly, the plasma-sheet material appears to be well mixed in
density
and temperature. An eddy viscosity for the plasma sheet is also estimated.
Power spectra, which are constructed from the v(t) and B(t)
time series, have
portions that are power laws with spectral indices that are near the range
of
those expected for turbulence theories. The plasma sheet may provide a
laboratory for the study of turbulence in parameter regimes different from
that
of solar-wind turbulence: the plasma sheet is a β[Gt ]1, hot-ion plasma,
and the
turbulence may be strongly driven rather than well developed. The turbulent
nature of the flow and the disordered nature of the magnetic field have
implications for the transport of plasma-sheet material, for the penetration
of
the solar-wind electric field into the plasma sheet, and for the calculation
of
particle orbits in the magnetotail.
Publisher
Cambridge University Press (CUP)
Cited by
259 articles.
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