DEMETER observations of high-latitude chorus waves penetrating the plasmasphere during a geomagnetic storm

Using the data of the DEMTER satellite during the magnetic storm on 14 April 2006, we study the storm time VLF electromagnetic waves, and find the first observational evidence of penetration of high-latitude chorus into the plasmasphere. During this geomagnetic storm, "banded" emissions of a few hertz to 20 kHz are observed to be intensified and to be organized in the frequency range of 0.1-0.5f_ce (equatorial electron cyclotron frequency) in high-latitude region of magnetic latitude between ∼40°and ∼60°. The signatures in the wave power spectra suggest that these emissions are likely lower-band chorus. The observed chorus waves are generally outside the plasmasphere. However, interestingly, these waves are observed inside the plasmasphere at regions with low L value during the main phase and early recover phase, which has never been reported in previous studies of chorus in low-latitude regions.