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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 28, issue 2
Ann. Geophys., 28, 569–576, 2010
https://doi.org/10.5194/angeo-28-569-2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 28, 569–576, 2010
https://doi.org/10.5194/angeo-28-569-2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

  15 Feb 2010

15 Feb 2010

Centrifugal acceleration in the magnetotail lobes

H. Nilsson1, E. Engwall2,3, A. Eriksson3, P. A. Puhl-Quinn4, and S. Arvelius1 H. Nilsson et al.
  • 1Swedish Institute of Space Physics, Kiruna, Sweden
  • 2Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
  • 3Swedish Institute of Space Physics, Uppsala, Sweden
  • 4Space Science Center, University of New Hampshire, Durham, NH, USA

Abstract. Combined Cluster EFW and EDI measurements have shown that cold ion outflow in the magnetospheric lobes dominates the hydrogen ion outflow from the Earth's atmosphere. The ions have too low kinetic energy to be measurable with particle instruments, at least for the typical spacecraft potential of a sunlit spacecraft in the tenuous lobe plasmas outside a few RE. The measurement technique yields both density and bulk velocity, which can be combined with magnetic field measurements to estimate the centrifugal acceleration experienced by these particles. We present a quantitative estimate of the centrifugal acceleration, and the velocity change with distance which we would expect due to centrifugal acceleration. It is found that the centrifugal acceleration is on average outward with an average value of about of 5 m s−2. This is small, but acting during long transport times and over long distances the cumulative effect is significant, while still consistent with the relatively low velocities estimated using the combination of EFW and EDI data. The centrifugal acceleration should accelerate any oxygen ions in the lobes to energies observable by particle spectrometers. The data set also put constraints on the effectiveness of any other acceleration mechanisms acting in the lobes, where the total velocity increase between 5 and 19 RE geocentric distance is less than 5 km s−1.

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