Studies of the signatures of magnetospheric substorms in coherent backscatter raders

Ground-based coherent backscatter radar systems are used extensively to investigate small-scale dynamics of the ionosphere and related geophysical processes in the magnetosphere. At high-latitudes, HF coherent backscatter radars are especially effective, as radio waves in the HF band undergo sufficient refraction to bring about the required magnetic field orthogonal configuration that enables backscatter. Much of the work in this thesis uses data from HF radars, looking in particular at effects in the data which can be detected during magnetospheric substorms. Typically, a total or partial loss of radar data occurs during substorm intervals, with a duration of some tens of minutes for an isolated event. This phenomenon lends itself to several possible explanations, for instance the radar propagation conditions may have altered, or the radar reception may have been affected by enhanced D-region absorption, or the scattering structure itself could become depleted by the substorm. Several examples of this phenomenon are considered in relation to these geophysical mechanisms, in order to determine which of these mechanisms might be the most significant in each case. For two events, there was electron density data available from an incoherent scatter radar, which was used to produce a model of the D-region absorption. This was compared with cosmic radio noise absorption data from an appropriately located imaging riometer, and then used to model the absorption of the HF radar as a function of elevation angle.