Exploring substorms with ULF waves (Invited)

Abstract:

The temporal sequence of events at substorm onset requires the generation and propagation of electromagnetic waves as the system evolves from its pre- to post-onset state. Such waves offer a unique diagnostic for the dynamics of this system, and the important coupling between the equatorial magnetosphere and auroral onset dynamics in the ionosphere.  ULF waves have been shown to be a pivotal aspect of the substorm onset process, their arrival denoting the epicentre of the magnetic and auroral displays in the ionosphere. However the magnetotail region to which this ULF wave epicentre maps is unknown.  Equally, what hinders progress in finding the ionospheric counterpart to magnetospheric features is the uncertainty in mapping high-precision but sparse magnetotail measurements of substorm-related phenomena into the ionosphere.

We review the properties of ULF waves before and during expansion phase onset, from ground-based magnetometry, auroral cameras and in-situ spacecraft.  We use ULF waves to provide new mapping capabilities in the magnetotail, as well as a means to remote sense the plasma physics of substorm onset itself.