Generation of simultaneous H+ and He+ band EMIC waves in the nightside radiation belt

Previous studies have shown that EMIC waves occur preferentially in the afternoon sector of the magnetosphere. Here we report obliquely propagating H+ and He+ band EMIC waves detected by Van Allen Probe B in the region of MLT=22.7–23.5 during the June 20, 2013 substorm. Using the correlated energetic proton data, we present continuous calculations on EMIC wave growth rates along the inward orbit in the region L=5.5−4.2. The modeled growth rate shows remarkable agreement with the observed double band EMIC waves in both temporal and spatial evolutions. The current results demonstrate that H+ and He+ band EMIC waves can be simultaneously excited in the midnight sector under appropriate conditions.