Direct Modulation of Electron Precipitation by ULF waves

Thursday, 8 March 2018: 09:30
Longshot and Bogey (Hotel Quinta da Marinha)
Alexander W Degeling, Shandong University at Weihai, Institute of Space Science, Weihai, China, Jonathan Rae, University College London, Mullard Space Science Laboratory, London, United Kingdom, Clare Watt, University of Reading, Reading, United Kingdom, Quanqi Shi, Shandong University at Weihai, Weihai, China and Robert Rankin, University of Alberta, Department of Physics, Edmonton, AB, Canada
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Abstract:
We present results from a bounce-average electron dynamics calculation in which magnetic field lines are perturbed by global scale ULF waves launched from the magnetopause in a 3D MHD wave model. We find that MHD fast waves in this model directly drive modulations in the population of electrons precipitating into the ionosphere, simply by their conservation of first and second adiabatic invariants (M and J). This can occur because the particular values of M and J for electrons mirroring at the top of the ionosphere are perturbed by changes in the magnetic field due to ULF waves, and oscillate in phase with the waves. The functional form of the electron phase space density expressed in terms of M and J therefore gives rise to modulations in the precipitating population. We consider how the modulation in precipitation by this mechanism may be expected to vary spatially at the ionosphere, based on Backward-Liouville-Test-Kinetic (BLTK) modelling using the bounce-average formalism, and compare against riometer and balloon observations [Rae et. al, J.Geophys. Res. under review; Spanswick et. al, Ann. Geophys. 2005].
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