Persistent Pitch Angle Anisotropies of Relativistic Electrons in the Outer Radiation Belts

Pitch angle distributions (PADs) in the radiation belts are well characterized with sinn(alpha). By tracking the exponent "n," termed pitch angle index, we are able to observe persistent and cross-energy changes in PADs of Van Allen radiation belt electrons using Van Allen Probes particle observations. The PAD measurements are well fit down to a single satellite spin, and therefore can track spatially and temporally confined changes to determine the connection between particles and waves. With this method, we study long-lasting and high-energy anisotropic electron PADs during a quiet period over 2 days, 26 and 27 June 2013. One potential driver for these changes is electromagnetic ion cyclotron wave interaction with the particles. We use several ground magnetometer stations from Canadian Array for Realtime Investigations of Magnetic Activity and Finnish pulsation magnetometer network of Sodankyla Geophysical Observatory to observe waves during the 2 days of interest. The connection between the waves and particles is inconclusive, although there is some temporal overlap of the phenomenon. The Van Allen Radiation belts can trap energetic electrons in the magnetic fields surrounding Earth. Often, these particles are studied during time periods of strong geomagnetic activity. However, quiet times can also result in interesting distributions and interactions in the radiation belts. We study one such geomagnetically quiet time where electron pitch angle distributions are suddenly and persistently anisotropic, as observed by instruments on the Van Allen Probes twin satellites. Neither probes observed electromagnetic waves that could cause anisotropic pitch angle distributions, but other satellites and ground measurements indicated wave activity during this time period. The connection between these two phenomenons is inconclusive. Persistent pitch angle distribution anisotropy is observed over 2 days associated with electromagnetic ion cyclotron (EMIC) wavesEMIC waves during geomagnetically quiet periods can have long lasting effect on radiation beltsMultipoint measurements can help pinpoint important mechanisms in radiation belt dynamics