Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm61a05e&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM61A-05 INVITED
Physics
2720 Energetic Particles, Trapped, 2752 Mhd Waves And Instabilities, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
Magnetometer data from several ground stations in Antarctica and particle and field data from the Polar, Wind, and GOES satellites are used to study characteristics of the flux tubes where unstructured electromagnetic ion cyclotron (EMIC) waves in the Pc 1-2 frequency band (0.1 to 0.4 Hz) are generated in the dayside outer magnetosphere during magnetospheric compressions. The wave events fall into two classes, "temporal" and "spatial." During temporal events, wave intensifications occurred simultaneously on the ground and in space, with no association with spatial variations in energetic protons. These events confirm the suggestion of Anderson and Hamilton [1993] that the outer dayside magnetosphere is often near marginal stability for EMIC wave generation, so waves can easily be stimulated by magnetospheric compressions. During spatial events, ground magnetometers observed steady, narrowband wave activity for the duration of major solar wind pressure increases while Polar encountered wave activity for only brief periods as it rapidly crossed outer magnetospheric L shells at relatively high magnetic latitudes (45° ). Particle data from Polar during these events show simultaneous enhanced fluxes of warm He+ ions and reduced fluxes of warm protons. These confirm previous observational and modeling studies that EMIC waves can heat He+ ions and produce perpendicular heating of equatorial protons, which will move their pitch angles away from the loss cone, and indicate that the waves have persisted on the given localized flux tubes for several tens of minutes. Wave events in this spatial category are also embedded in radially extended regions with ring-like, moderately anisotropic distributions of >5 keV protons, but occur only in association with localized radial gradients in highly anisotropic ~1 keV protons rather than near the magnetospheric boundary. During the brief wave bursts both of these populations fill the loss cone, which suggests that both are sources of free energy for the waves. This unexpected association of waves with increased fluxes of ~1 keV protons indicates an important but unanticipated role for these highly structured convecting protons in destabilizing localized regions the outer dayside magnetosphere to EMIC waves.
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