Similar observations of substorms can be obtained with HF radar and this is an increasingly important area of research due to the abundance of HF radars occupying the globe as a result of the SuperDARN initiative. However, the use of HF provides significantly more challenges in the study of magnetospheric processes. In this frequency range, the radar rays are more sensitive to both refraction and absorption. In consequence, the intense particle precipitation at substorm onset can lead to the total loss of scatter.
Perhaps due to the difficulties encountered in studying substorm onset and expansion phases, the bulk of initial HF observations address growth phase phenomena, e.g. Lewis et al. (1998), Uspensky et al. (2000), Yeoman et al. (1999), Voronkov et al. (1999), Lester et al. (1998) and Watanabe et al. (1998). However, the onset and expansion phase have now been looked at in more detail notably by Milan et al. (1999) and Yeoman et al. (1998a, 1998b, 2000).
The global nature of SuperDARN now allows large scale, e.g. global convection, features of substorms to be studied. Fox et al (1992) perhaps made the first attempt at this when SuperDARN was in its infancy by combining measurements of Goose Bay with SABRE and other instruments. More recently Greenwald and Gallagher (1998) have studied the connection between dayside reconnection, the increase in polar cap potential and convection, which can occur concurrently with the growth and expansion phases of substorms.
Lester (2000) has compiled a detailed review of the above topics.