Effects of disturbances in the magnetosheath on the EMIC wave and its characteristics

Abstract:

It is generally believed that electromagnetic ion cyclotron (EMIC) waves are generated by temperature anisotropy. However, statistical studies have shown the high occurrence rate of EMIC waves in the outer magnetosphere without temperature anisotropy. Recently, it is suggested that the disturbances in the magnetosheath flow can excite broadband EMIC sources by using both theoretical and numerical models. We investigate with spacecraft data whether disturbances in the magnetosheath and EMIC waves in the outer magnetosphere are correlated. We present that the flow disturbances affect EMIC wave occurrences and the EMIC frequencies are sensitive to the size and/or intervals of disturbances. Our results show that observational features are consistent with the models above.