Physics – Plasma Physics
Scientific paper
Oct 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11610205c&link_type=abstract
Journal of Geophysical Research, Volume 116, Issue A10, CiteID A10205
Physics
Plasma Physics
Magnetospheric Physics: Mhd Waves And Instabilities (2149, 6050, 7836), Magnetospheric Physics: Solar Wind/Magnetosphere Interactions, Space Plasma Physics: Mhd Waves And Instabilities (2149, 2752, 6050), Space Plasma Physics: Wave/Particle Interactions (2483, 6984)
Scientific paper
We identified 1875 wave events in magnetic field data from geosynchronous orbit. Most of these events were transverse with respect to the background magnetic field, left-hand polarized, and were observed in the post-noon magnetic local time sector at frequencies just below the helium gyrofrequency. Combined, these observations strongly suggest that most of these events are Electromagnetic Ion Cyclotron (EMIC) waves. Average wave amplitudes are presented, binned by frequency, geomagnetic activity and magnetic local time. The amplitude increases with increasing geomagnetic activity; increased activity also narrows the local time sector in which the waves are observed. A superposed epoch analysis of solar wind parameters and geomagnetic activity indices shows that 12 hours before wave onset the AE and Kp index increased, indicating storm and substorm activity that injects hot ion populations needed to drive the EMIC instability and providing ample time for those populations to drift into the post-noon local time sector. Just before wave onset a sudden enhancement in the AE index and the solar wind dynamic pressure are observed, indicating that a final perturbation of the magnetosphere is needed to excite EMIC wave growth. EMIC waves are thought to cause loss of relativistic particles in the radiation belt. Large solar wind densities have been associated with low flux of relativistic particles during the recovery phase of geomagnetic storms. We show that EMIC waves are preferentially generated during intervals of large solar wind density, indicating that such conditions drive EMIC waves which in turn cause enhanced loss of relativistic particles.
Baker B. H. J.
Clausen B. N. L.
Ruohoniemi Michael J.
Singer Howard J.
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