Magnetospheric electric and magnetic perturbations at ultralow frequencies (ULF, between 2 and 25 megahertz) can accelerate energetic particles in the magnetosphere and thus affect orbiting satellites. However, not all classes of ULF waves are important for electron acceleration. To learn more, Sarris et al. study data from an unusual source: the five-probe constellation of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, launched in 2007 to study magnetospheric substorms.

Through recognizing that the alignment and orbits of the THEMIS probes, particularly in the first period of its mission, provided unique opportunities to study ULF pulsations in the magnetosphere, the authors identify specific electric and magnetic field disturbances that are shown through modeling and observation to be resonances of the magnetic field lines. They then use phase-difference calculations between probes to estimate the number of fluctuations present at a given time. The authors expect that further research will help understand the dynamics of the Earth’s radiation belts.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036732, 2009; http://dx.doi.org/10.1029/2008GL036732