EMICWave Properties Associated With and Without Injections in The Inner Magnetosphere

摘要

To understand the generation and propagation processes of electromagnetic ion cyclotron (EMIC) waves under different geomagnetic conditions in the inner magnetosphere, we performed a statistical study of EMIC wave properties observed by the Van Allen Probes from February 2013 to December 2016. We divided EMIC waves into two groups: those associated with and those occurring without injections observed by the Geostationary Operational Environmental Satellites (GOES-13 and GOES-15).We found that the EMIC wave polarization sense ε increased and the normalized frequency X decreased with increasing |MLAT|. Inside the plasmasphere, He~+ EMIC waves were predominantly observed with left-hand polarization (ε<-0.3) and higher wave normal angles (θ_k = 30-40° ). Those associated with injections showed the most intense wave power at 14-16 MLT, compared to periods without injections when these waves exhibit a similar wave power but on the dayside. H+ EMIC waves were predominantly observed outside the plasmasphere on the dayside and showed a mixture of left-hand and linear polarizations (ε= -0.3-0.0) with lower wave normal angles (θ_k = 20-30° ) regardless of injections. Moreover, H~+ EMIC waves were accompanied by a solar wind dynamic pressure enhancement (?Psw = 0.5 nPa). From these observations, we suggest that hot injected plasma contributes to the generation of intense He~+ EMIC waves in the afternoon sector. A mixture of expanding cold plasmaspheric ions and coexisting hot ring current ions acts as the free energy source for He~+ EMIC waves on the dayside during quiet times. Solar wind dynamic pressure enhancements are likely the major driver of H~+ EMIC waves outside the plasmasphere.