Introduction

Radars sensitive to field-aligned plasma irregularities are both an informative and challenging diagnostic for the study of magnetospheric processes. The challenge is that the characteristics and behaviour of the irregularities have a complex relationship to such quantities as the electric fields, conductivities and plasma densities which are often the signatures of the magentospheric process under study. However, once this is understood, radars provide versatile and sensitive techniques for such solar terrestrial research.

 

Figure 1:

The study of magnetospheric substorms is an outstanding example. In Figure 1 a plot from the MIRACLE network is displayed exhibiting from top to bottom, a measure of the local AE index, the Bx cpt from a subset of the the IMAGE array, keograms from Longyearbyen and Kilpisjarvi, overlaid with a plot of the electrojet boundaries (an estimate from the magnetometer data) and in the bottom panels the radar backscatter power and velocity from the STARE Norwegian radar. During the interval a substorm onset occurs at approximately 22:00 UT. There are clear signatures of this in the increase in the AE index, the negative bays in the magnetometer time series, the equatorward and then poleward motion of the electrojets and luminosity in the KIL keogram at onset.

The bottom panels of VHF radar data are an excellent example of how coherent backscatter radars can image magnetospheric substorms. Clear growth phase signatures are observed as the region of backscatter confined in range moves equatorward from 2120 to 2200 UT. At onset there is poleward motion of the scattering region. The expansion and recovery phase is then characterised by rich scatter at all ranges. This type of observation is not atypical for the STARE radar.