Multipoint Measurements of Injection Region Evolution in the Inner Magnetosphere
Abstract:The Dispersionless Injection (DI) region is the source of substorm associated enhancements in high energy particle flux (10s to 100s of keV). At any given time as it unfolds, DI is occurring across an extended region near the inner edge of the thin current sheet. This region forms around the time of substorm onset and evolves radially inward towards the ring current region. The Earthward edge of the injection region (the injection front) is capable of penetrating deep into the inner magnetosphere, providing a key seed population for the ring current, the radiation belts, and high-energy electron precipitation that affects atmospheric composition and technologies that rely on radio propagation through the upper atmosphere. Typically observed with in situ particle detectors, our knowledge of the injection front and the fate of injected particles is limited by the number and location of spacecraft observations. In this paper, we present multipoint observations of substorm injections in the Canadian sector derived from coordinated THEMIS and ground-based riometer measurements. The combined information of ground and in situ data provides key information about injection region evolution and the loss of injected particles in the inner magnetosphere. Utilizing more than twenty-five riometers operating in Canada and Scandinavia during the THEMIS era, we are able to constrain spacecraft observations in MLT and latitude/radial location, as well as monitor the precipitation from the resulting drifting electron population (the dispersed injections).
Focusing on the 1624 dispersionless electron injection events discussed in Gabrielse et al. (2014), we present statistics of injection location and radial evolution as well as parameters such as radial penetration depth, ionospheric energy deposition and the relationship between them. We also present detailed examples of events in which THEMIS and the ground observations provide a complete picture of the injection region evolution. We will finish with a discussion of the implications of our results on competing theories as to how and where DIs begin (see e.g., Kabin et al., 2011 and Gabrielse et al., 2012).