Coherent scatter radar observations of field line resonances and flux transfer events

• Main Author: Provan, Gabrielle
• Published: University of Leicester 1998
• Subjects: 538
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.696515

The Earth's magnetosphere is constantly being perturbed by its interaction with the solar wind and the interplanetary magnetic field (IMF). This thesis involves a study of the ionospheric signatures of two separate processes which arise in the magnetosphere through these interactions, namely field line resonances and flux transfer events. Field line resonances - standing magnetohydrodynamic waves - have previously been observed as a periodic modulation of the plasma drift velocity by the Goose Bay HF and SABRE VHF coherent scatter radars. They produce latitudinally-structured spectral peaks at ultra low frequencies (1 to 6 mHz) observed predominantly during the night and early morning (0000 to 0600 MLT). A comparison of the spectra observed by the Goose Bay and SABRE radars demonstrates that the frequencies of the field line resonances are, on average, almost identical despite the different latitudinal ranges covered by the two radars. Possible explanations for the similarity of the signatures on the two radar systems are discussed. The CUTLASS Finland HF coherent radar has been run in a two-beam special scan mode, which offered excellent temporal and spatial information on the plasma convection flow in the high-latitude ionosphere. A detailed study of one day of this data revealed a number of pulsed drift enhancements, seemingly moving away from the radar. These transients are identified here as the ionospheric signature of flux transfer events (FTEs), transient reconnection between the IMF and magnetosphere. The transient signatures are used to produce an average mapping of newly reconnected field lines, calculated by analysing two years of both high-time resolution and normal scan data from the CUTLASS Finland radar. It is shown that the coherent scatter observations are consistent with the precipitation regimes observed by low-altitude satellites and the cusp signature predictions of the Lockwood (1997) and Onsager and Lockwood (1997) model of dayside reconnection phenomena.