Speaker
Clare Emily Jane Watt
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.404.pdf
Multiple manifestations of whistler-mode wave-particle interactions in
Earth’s Outer Radiation Belt
C. E. J. Watt1, H. Ratcliffe2, O. Allanson1, D. Verscharen3, R. B. Horne4, N. Meredith4, S.
Glauert4
1
University of Reading, Reading, UK, 2University of Warwick, Coventry, UK, 3Mullard Space
Science Laboratory, UCL, Holmbury St Mary, UK, 4British Antarctic Survey, Cambridge, UK
The Earth’s Outer Radiation Belt is a highly-variable region of high-energy electrons that forms
a torus spanning 2.5-7 Earth radii from our planet. In this region, the number flux of electrons
of energies between 100keV to a few MeV can vary by an order of magnitude in a matter of
hours. It is now widely understood that a large contribution to the variability in the Outer
Radiation Belt is wave-particle interactions in the collisionless natural plasma environment of
the Earth’s magnetosphere. Many different wave modes, across a large frequency range, are
important for the dynamics of the Outer Radiation Belt, but here we focus on the physics of the
whistler-mode interaction with electrons in all its different manifestations.
The whistler-mode wave is a right-hand polarised electromagnetic wave mode with frequency
between the proton and electron gyrofrequency that displays different characteristics in
different parts of the magnetosphere. Evidence of temperature anisotropy and beam-driven
instabilities both exist, but some magnetospheric whistler-mode waves are generated in the
terrestrial atmosphere during lightning strikes (true “whistlers”), and some from man-made
transmitters on Earth’s surface. Additionally there is evidence that waves are naturally
generated in one part of the magnetosphere and propagate through the inner magnetosphere to
other locations where the wave-particle interaction changes due to different ambient plasma
conditions [e.g. Bortnik et al., 2008].
We use linear and quasilinear theory and fully nonlinear numerical experiments to study both
acceleration and loss of electrons in the Outer Radiation Belt of Earth as a result of all the
different manifestations of whistler-mode waves. We compare and contrast the observational
evidence for different types of whistler-mode waves in the magnetosphere and discuss the
theoretical approaches suitable to study the wave-particle interactions that result.
Bortnik, J., R. M. Thorne and N. P. Meredith (2008), The Unexpected origin of plasmaspheric hiss from discrete
chorus emissions, Nature, 452, 62-66, doi:10.1038/nature06741
