Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm51c..02j&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM51C-02
Physics
2716 Energetic Particles, Precipitating, 2753 Numerical Modeling, 2772 Plasma Waves And Instabilities, 2778 Ring Current, 2788 Storms And Substorms
Scientific paper
During storm conditions the ring current ion distributions are often unstable and can generate electromagnetic ion cyclotron (EMIC) waves with amplitudes above 1 nT. The subsequent interaction of energetic particles with these waves results in pitch angle scattering on short timescales and intense precipitation to the atmosphere. We simulate the dynamical evolution of the ring current during several large and great geomagnetic storms and investigate the effect of resonant interactions of ring current ions with EMIC waves on the early ring current decay. The initial and boundary conditions of our kinetic drift-loss model are inferred from measurements from the hot plasma instruments on the POLAR spacecraft and the geosynchronous LANL satellites. We calculate the growth rate of EMIC waves considering for the first time wave excitation not only in the frequency range between the He+ and O+ gyrofrequencies, but also at frequencies below O+ gyrofrequency. A time-dependent global wave model is constructed and the spatial and temporal evolution of precipitating ion fluxes is determined. We find that the most unstable regions form after intensification of the ring current, i.e., near Dst minimum, and occur in the duskside local time sector. The wave gain of O+ band waves exceeds the magnitude and is located at larger L shells than that of the He+ band waves during the great storms. The global EMIC wave activity predicted by our model compares reasonably well to storm time satellite observations. The relative contribution of losses due to charge exchange, Coulomb collisions, atmospheric collisions at low altitudes, and wave-particle interactions along adiabatic drift paths is calculated during different storm phases and intercompared.
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