The occurrence and wave properties of EMIC waves observed by the Magnetospheric Multiscale (MMS) mission

Electromagnetic ion cyclotron (EMIC) waves can precipitate the ring current ions and relativistic electrons and heat the cold electrons in the magnetosphere. This requires comprehensive knowledge of the occurrence and wave properties of EMIC waves. In the present study, we used the data from one new mission, the Magnetospheric Multiscale (MMS) mission launched in March 2015, to investigate the occurrence and wave properties of H+-band and He+-band EMIC waves in the magnetosphere. Our statistical results show the following: (1) H+-band EMIC waves mostly occur in the higher L-shells (L>5) while He+-band EMIC waves are mostly observed in the lower L-shells (L<6). (2) The occurrence rate of H+-band EMIC waves in the dayside is higher than that in the nightside. The highest peak of occurrence rate of H+-band EMIC waves is in the postnoon sector (5-8 L-shells), and the secondary peak lies in the small area of the dawn sector. (3) The wave power spectral density peaks in the postnoon and predusk sectors, while the wave normal angles are largest in the dawn sector. (4) Linear and right-hand polarized H+-band EMIC waves are mainly in the regions of peak occurrence, while linear polarized waves are seen to also dominate outside of the regions of peak occurrence. The highest occurrence rate of linear polarized He+-band EMIC waves is observed in the dawn sector. We discussed the results and compared with previous findings.