Nature's Grand Experiment: Linkage between magnetospheric convection and the radiation belts

Abstract

The solar minimum of 2007–2010 was unusually deep and long lived. In the later stages of this period the electron fluxes in the radiation belts dropped to extremely low levels. The flux of relativistic electrons (>1 MeV) was significantly diminished and at times was below instrument thresholds both for spacecraft located in geostationary orbits and also those in low‐Earth orbit. This period has been described as a natural “Grand Experiment” allowing us to test our understanding of basic radiation belt physics and in particular the acceleration mechanisms which lead to enhancements in outer belt relativistic electron fluxes. Here we test the hypothesis that processes which initiate repetitive substorm onsets drive magnetospheric convection, which in turn triggers enhancement in whistler mode chorus that accelerates radiation belt electrons to relativistic energies. Conversely, individual substorms would not be associated with radiation belt acceleration. Contrasting observations from multiple satellites of energetic and relativistic electrons with substorm event lists, as well as chorus measurements, show that the data are consistent with the hypothesis. We show that repetitive substorms are associated with enhancements in the flux of energetic and relativistic electrons and enhanced whistler mode wave intensities. The enhancement in chorus wave power starts slightly before the repetitive substorm epoch onset. During the 2009/2010 period the only relativistic electron flux enhancements that occurred were preceded by repeated substorm onsets, consistent with enhanced magnetospheric convection as a trigger.

Energetic Particle Data From the Global Positioning System Constellation

“…This article has given an overview of the 16 years (>167 satellite years) of GPS data that have been released. The CXD electron fluxes, which have previously been shown to be of high quality [ Morley et al , ], clearly show the dynamics of the outer electron radiation belt during this time and are consistent with previous work [e.g., Baker and Blake , ; Rodger et al , ; Reeves et al , ]. The LANL‐GPS data allow mapping of the outer electron radiation belt with unprecedented data density [see, e.g., Morley et al , ] but enable a wealth of other studies.…”

What effect do substorms have on the content of the radiation belts?

“…However, whistler mode chorus waves are also implicated in pitch angle scattering that can move particles into the loss cone [ Horne and Thorne , ]. Similarly, EMIC waves can efficiently scatter particles into the loss cone [ Meredith et al ., ; Bortnik et al ., ; Hendry et al ., ; Usanova et al ., ; Rodger et al ., ]. A modeling study by Li et al .…”

Long‐term geomagnetically induced current observations in New Zealand: Earth return corrections and geomagnetic field driver

“…Note that 2010 was used as it was a comparatively quiet year geomagnetically, if not as quiet as 2009 (for example, see the discussion in Rodger et al . []). Comparing this cleaned product to the original data shows how important correcting for HVDC operation is when considering the New Zealand DC data set.…”