Utilising long term radio observations of auroral kilometric radiation to explore magnetosphere-ionosphere coupling

Abstract

Auroral Kilometric Radiation (AKR) is Earth’s most powerful, naturally-emitted radio emission. It is a direct result of the dynamics of energetic electrons along high latitude magnetic field lines in the magnetosphere-ionosphere coupling region and is useful for inference of the spatial morphology and activation of the auroral acceleration region. In this thesis, a novel technique is developed to retrieve calibrated AKR observations from the Wind spacecraft, without the presence of solar and other contaminating radio emissions. Wind houses a remote-sensing radio observatory and has been active since 1995, providing the longest dataset of AKR from many viewing positions around the Earth. For AKR, which is anisotropically beamed, this breadth of data allows the effect of the observer position to be characterised. Subsequently, the data are used to explore AKR dynamics and corresponding changes in the auroral acceleration region during substorms and other disturbed periods. Firstly, the AKR selection is applied to a 30 day period during the Earth flyby of the Cassini spacecraft for a multipoint observation. Comparing the temporal modulation of the AKR power from both spacecraft during this period, it is shown that a diurnal modulation is likely due to the geometrical effect of the rotating magnetic dipole, but also sees intrinsic source modulation common to both hemispheres. Secondly, the selection is applied to 10 years of observations that overlap with published lists of substorm onsets. After accounting for viewing, the average AKR power in low and high frequency bands was examined during the substorm timeline. This demonstrated that higher altitude AKR sources provide a greater contribution during substorm onset on average, and that this relative contribution scales with the level of disturbance. Finally, dayside observations of AKR were used during the arrival of a coronal mass ejection (CME) at Earth. While showing that Wind’s dayside observations can be used as a metric for magnetospheric activity, coincident observations of the UV aurora were used to constrain the auroral origin, namely intense, dayside auroral dynamics related to an ongoing substorm.

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Identifiers

ORCID for James Waters: orcid.org/0000-0001-8164-5414

ORCID for Daniel Whiter: orcid.org/0000-0001-7130-232X

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