A statistical study of EMIC waves and associated plasma conditions in the inner magnetosphere: Cluster observations

In the Earth's magnetosphere, electromagnetic ion cyclotron (EMIC) waves are normally excited by an anisotropic distribution of energetic (a few tens of keV) H⁺ in the ring current or plasma sheet. The generation and propagation of EMIC waves are also profoundly controlled by other plasma parameters such as ion composition, cold heavy plasma, and energetic H⁺ density. During the time period of 1 March 2001 - 31 December 2009, about 200 time intervals of EMIC wave activity are identified from the wavelet spectrograms of high-resolution (22.4 vectors/second) magnetic field data from the Fluxgate Magnetometer (FGM) on board Cluster in the inner magnetosphere. Those EMIC wave intervals, lasting for a few to tens of minutes, predominantly occurred on the dayside (L = 4-15) and at low/middle magnetic latitudes (MLAT = -50°-45°). In this study, using in situ plasma and magnetic field measurements on Cluster, upstream solar wind data, and geomagnetic indices (i.e., Dst and Kp), we perform a statistical study of the wave periods to investigate the occurrence conditions for the waves, including the local plasma conditions, the solar wind plasma/interplanetary magnetic field (IMF) conditions, and geomagnetic activity.