Conjugate Multisatellite Observations of EMIC Pc 1 Waves and Associated Proton Precipitation

We present coordinated ground-satellite observations of compression-related dayside electromagnetic ion cyclotron (EMIC) waves from 25th September 2005. The EMIC waves appear in coincidence with enhanced solar wind dynamic pressure, following several days of quiet geomagnetic conditions. On the ground the EMIC wave activity was observed by the CARISMA magnetometer array (http://www.carisma.ca) for several hours simultaneously with the enhancement in solar wind pressure. Two Cluster satellites observed the EMIC waves for half an hour as they consecutively crossed the same region of space. Multipoint space-ground observations enabled us to determine the location of the waves in the magnetosphere and conclude that the EMIC wave activity was preferentially exited within a region of high plasma density close to the plasmapause (L=5), as monitored by the Cluster spacecraft potential and supported by ground-based cross-phase analysis. Simultaneously with the EMIC activity on Cluster, the NOAA spacecraft registered a localized enhancement of precipitating protons with energies > 30 keV in the low-altitude region over Canada, conjugate to both Cluster and CARISMA. Our observations suggest that the interaction of energetic ring current protons with EMIC waves takes place in the vicinity of the plasmapause, in this case following a sustained period of quiet geomagnetic activity.