Ann. Geophys., 39, 31–51, https://doi.org/10.5194/angeo-39-31-2021,https://doi.org/10.5194/angeo-39-31-2021, 2021
The electrical conductivity of the Earth's ionosphere is an important parameter in the study of the polar,
auroral currents that produce magnetic disturbances on the ground. Yet the values of the conductances, and
how they vary, are not known with great precision. In our study we tested a method for deriving the conductivity
values that requires use of three empirical models for the electric fields above the ionosphere and the
magnetic field perturbations both on the ground and in space.
Herbert Gunell, Charlotte Goetz, Elias Odelstad, Arnaud Beth, Maria Hamrin, Pierre Henri, Fredrik L. Johansson, Hans Nilsson, and Gabriella Stenberg Wieser
Ann. Geophys., 39, 53–68, https://doi.org/10.5194/angeo-39-53-2021,https://doi.org/10.5194/angeo-39-53-2021, 2021
When the magnetised solar wind meets the plasma surrounding a comet, the magnetic field is enhanced in front of the comet, and the field lines are draped around it. This happens because electric currents are induced in the plasma. When these currents flow through the plasma, they can generate waves. In this article we present observations of ion acoustic waves, which is a kind of sound wave in the plasma, detected by instruments on the Rosetta spacecraft near comet 67P/Churyumov–Gerasimenko.
Noora Partamies, Fasil Tesema, Emma Bland, Erkka Heino, Hilde Nesse Tyssøy, and Erlend Kallelid
Ann. Geophys., 39, 69–83, https://doi.org/10.5194/angeo-39-69-2021,https://doi.org/10.5194/angeo-39-69-2021, 2021
About 200 nights of substorm activity have been analysed for their magnetic disturbance magnitude and the level of cosmic radio noise absorption. We show that substorms with a single expansion phase have limited lifetimes and spatial extents. Starting from magnetically quiet conditions, the strongest absorption occurs after 1 to 2 nights of substorm activity. This prolonged activity is thus required to accelerate particles to energies, which may affect the atmospheric chemistry.