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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-2020-11
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2020-11
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: regular paper 17 Mar 2020

Submitted as: regular paper | 17 Mar 2020

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This preprint is currently under review for the journal ANGEO.

Horizontal electric fields from flow of auroral O+(2P) ions at sub-second resolution

Sam Tuttle1, Betty Lanchester1, Bjoern Gustavsson2, Daniel Whiter1, Nickolay Ivchenko3, Robert Fear1, and Mark Lester4 Sam Tuttle et al.
  • 1Physics and Astronomy, University of Southampton, Southampton, UK
  • 2Department of Physics and Technology, University of Tromsø, Tromsø, Norway
  • 3KTH, Royal Institute of Technology, Stockholm, Sweden
  • 4Department of Physics and Astronomy, University of Leicester, Leicester, UK

Abstract. Electric fields are a ubiquitous feature of the ionosphere and are intimately linked with aurora through particle precipitation and field-aligned currents. We present a unique method to estimate ionospheric electric fields beside a dynamic auroral feature by solving the continuity equation for the metastable O+(2P) ions, which emit as they move under the influence of electric fields during their 5 s lifetime. Simultaneous measurements of emission at 732.0 nm (from the O+(2P) ions), and prompt emissions at 673.0 nm (N2) and 777.4 nm (O), all at high spatial (100 m) and temporal (0.05 s) resolution, are used in the solution of the continuity equation, which gives the dynamic changes of the O+ ion population at all heights in a 3D volume close to the magnetic zenith. Perspective effects are taken into account by a new geometric method, which is based on an accurate estimate of the magnetic zenith position. The emissions resulting from the metastable ions are converted to brightness images by projecting onto the plane of the ground, which are compared with the measured images. The flow velocity of the ions is a free parameter in the solution of the continuity equation; the value that minimizes the difference between the modelled and observed images is the extracted flow velocity at each time step. We demonstrate the method with an example event during the passage of a brightening arc feature, lasting about 10 s, in which the inferred electric fields vary between 20 and 120 mV m−1. These inferred electric fields are compared with SuperDARN measurements, which have an average value of 30 mV m−1. An excellent agreement is found in magnitude and direction of the background electric field; an increase in magnitude during the brightening of the arc feature supports theories of small scale auroral arc formation and electrodynamics.

Sam Tuttle et al.

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Sam Tuttle et al.

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Latest update: 06 Apr 2020
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Short summary
Electric fields in the atmosphere near dynamic aurora are important in the physics of the electric circuit within the earth's magnetic field. Oxygen ions emit light as they move under the influence of these electric fields; the flow of this emission is used to find the electric field at high temporal resolution. The solution needs two other simultaneous measurements of auroral emissions to give key parameters such as the auroral energy. The electric fields increase with brightness of the aurora.
Electric fields in the atmosphere near dynamic aurora are important in the physics of the...
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