Chorus variation during the compression of magnetosphere

Chorus is important in space science due to its role in generation of relativistic electrons in the Van Allen radiation belts, which are hazardous to satellites and astronauts. Although chorus has been studied for several decades and many theories have been proposed, its generation and growth mechanisms are still not well understood. In this manuscript, we show an unexpected observation, based on measurements from the NASA THEMIS satellites, that chorus can be significantly amplified when an interplanetary shock that originates from Sun hits Earth's magnetosphere. The shock-induced anisotropic distribution of energetic electrons leads to the growth of chorus.