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Journal of Geophysical Research: Space Physics

Average plasma properties in the central plasma sheet


  • W. Baumjohann,

  • G. Paschmann,

  • C. A. Cattell


Using four months of tail data obtained by the three-dimensional plasma instrument on board the AMPTE/IRM satellite in 1986, we have done a statistical survey on the behavior of ion and electron moments in the central plasma sheet. Almost 80,000 spin averages of plasma density, ion bulk velocity, ion and electron temperature, and plasma β were analyzed with respect to differences between their values in the inner and outer central plasma sheet as well as their dependence on magnetic activity. The ion temperature increases with increasing magnetic activity while the ion density decreases during disturbed intervals, except in the neutral sheet neighborhood at smaller radial distances. The ion and electron temperatures in the central plasma sheet are highly correlated, with Ti/Te being constant over a wide range of temperatures and about twice as large as in the distant tail. The average ion flow speeds in the central plasma sheet are below 100 km/s and nearly identical to those found in the plasma sheet boundary layer, although the distribution functions usually are quite different. High-speed flows do occur, but in bursts of most often less than 1 min duration with intermittent intervals of nearly stagnant plasma. The distribution of flow directions strongly favors sunward flow for velocities above 300 km/s, indicating that a near-earth neutral line is rarely, if ever, located inside of XGSM = −19 RE.

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