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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-59
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-59
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 24 Apr 2019

Regular paper | 24 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Hybrid-Vlasov modelling of nightside auroral proton precipitation during southward interplanetary magnetic field conditions

Maxime Grandin1, Markus Battarbee1, Adnane Osmane1, Urs Ganse1, Yann Pfau-Kempf1, Lucile Turc1, Thiago Brito1, Tuomas Koskela1, Maxime Dubart1, and Minna Palmroth1,2 Maxime Grandin et al.
  • 1University of Helsinki, Department of Physics, Finland
  • 2Finnish Meteorological Institute, Helsinki, Finland

Abstract. Particle precipitation plays a key role in the coupling of the terrestrial magnetosphere and ionosphere by modifying the upper atmospheric conductivity and chemistry, driving field-aligned currents, and producing aurora. Yet, quantitative observations of precipitating fluxes are limited, since ground-based instruments can only provide indirect measurements of precipitation while particle telescopes onboard spacecraft merely enable point-like in-situ observations with inherently coarse time resolution above a given location. Further, orbit time scales generally prevent the analysis of whole events. On the other hand, global magnetospheric simulations can provide estimations of particle precipitation with a global view and higher time resolution. We present the first results of auroral (~ 1–30 keV) proton precipitation estimation using the Vlasiator global hybrid-Vlasov model in a noon-midnight meridional plane simulation driven by steady solar wind with southward interplanetary magnetic field. We first calculate the bounce loss cone angle value at selected locations in the simulated nightside magnetosphere. Then, using the velocity distribution function representation of the proton population at those selected points, we study the population inside the loss cone. This enables the estimation of differential precipitating number fluxes as would be measured by a particle detector onboard a low-Earth-orbiting spacecraft. The obtained differential flux values are in agreement with a well-established empirical model in the midnight sector, as are also the integral energy flux and mean precipitating energy. We discuss the time evolution of the precipitation parameters derived in this manner in the global context of nightside magnetospheric activity in this simulation, and we find in particular that precipitation bursts of < 1 min duration can be self-consistently and unambiguously associated with dipolarising flux bundles generated by tail reconnection. We also find that the transition region seems to partly regulate the transmission of precipitating protons to the inner magnetosphere, suggesting it has an active role in regulating ionospheric precipitation.

Maxime Grandin et al.
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Latest update: 19 May 2019
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Short summary
When the terrestrial magnetic field is disturbed, particles from the near-Earth space can precipitate into the upper atmosphere. This work presents for the first time numerical simulations of proton precipitation in the energy range associated with the production of aurora (~ 1–30 keV) using a global kinetic model of the near-Earth space: Vlasiator. We find that nightside proton precipitation can be regulated by the transition region between stretched and dipolar geomagnetic field lines.
When the terrestrial magnetic field is disturbed, particles from the near-Earth space can...
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