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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 5 | Copyright
Ann. Geophys., 36, 1439-1456, 2018
https://doi.org/10.5194/angeo-36-1439-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 23 Oct 2018

Regular paper | 23 Oct 2018

Dynamics of a geomagnetic storm on 7–10 September 2015 as observed by TWINS and simulated by CIMI

Joseph D. Perez1, James Edmond1, Shannon Hill2, Hanyun Xu1, Natalia Buzulukova3, Mei-Ching Fok3, Jerry Goldstein4,5, David J. McComas6, and Phil Valek4,5 Joseph D. Perez et al.
  • 1Department of Physics, Auburn University, Auburn, AL 36849, USA
  • 2Physics Department, Emory University, Atlanta, GA 30322, USA
  • 3Geospace Physics, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 4Space Science and Engineering Department, Southwest Research Institute, San Antonio, TX 78228, USA
  • 5Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249, USA
  • 6Department of Astrophysical Sciences, Princeton University, NJ 08540, USA

Abstract. For the first time, direct comparisons of the equatorial ion partial pressure and pitch angle anisotropy observed by TWINS and simulated by CIMI are presented. The TWINS ENA images are from a 4-day period, 7–10 September 2015. The simulations use both the empirical Weimer 2K and the self-consistent RCM electric potentials. There are two moderate storms in succession during this period. In most cases, we find that the general features of the ring current in the inner magnetosphere obtained from the observations and the simulations are similar. Nevertheless, we do also see consistent contrasts between the simulations and observations. The simulated partial pressure peaks are often inside the observed peaks and more toward dusk than the measured values. There are also cases in which the measured equatorial ion partial pressure shows multiple peaks that are not seen in the simulations. This occurs during a period of intense AE index. The CIMI simulations consistently show regions of parallel anisotropy spanning the night side between approximately 6 and 8RE, whereas the parallel anisotropy is seen in the observations only during the main phase of the first storm. The evidence from the unique global view provided by the TWINS observations strongly suggests that there are features in the ring current partial pressure distributions that can be best explained by enhanced electric shielding and/or spatially localized, short-duration injections.

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Pressure and anisotropy profiles from trapped ions in the ring current as observed from energetic neutral atom images are compared to numerical simulations for the first time. The results show evidence for short time and spatially localized injections from the plasma sheet.
Pressure and anisotropy profiles from trapped ions in the ring current as observed from...
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