Observational evidence for the role of Hall conductance in Alfvén wave
reflection
Abstract
Electromagnetic energy carried by magnetohydrodynamic modes is an
important mechanism in the energy transfer between the magnetosphere and
the ionosphere. Through wave reflection in the ionosphere, Alfvén waves
are known to carry field-aligned currents, and thus play an important
role in the dynamics of the ionosphere-magnetosphere coupling. The role
of Hall conductance in this interplay has been explored in
magneto-hydrodynamic models of the ionosphere, but has hitherto not been
observed in-situ. We use five years of observations from the Swarm
mission to shed light on this interplay. We present the high-latitude
climatology of both the measured Poynting flux and the measured Alfvén
wave reflection coefficient. Our results indicate that high-energy
deeply penetrating precipitation, which directly leads to strongly
enhanced Hall conductance, is an important cause of positively
interfering Alfvén wave reflection. We present such observational
evidence, and with that, suggest that Hall conductance is substantially
more important in the ionospheric wave reflection climatology than
hitherto believed.