Electromagnetic cyclotron waves in the dayside subsolar outer magnetosphere generated by enhanced solar wind pressure: EMIC wave coherency

摘要

Electromagnetic ion (proton) cyclotron (EMIC) waves and whistler mode chorus are simultaneously detected in the Earth's dayside subsolar outer magnetosphere. The observations were made near the magnetic equator 3.1 degrees-1.5 degrees magnetic latitude at 1300magnetic local time from L = 9.9 to 7.0. It is hypothesized that the solar wind external pressure caused preexisting energetic 10-100keV protons and electrons to be energized in the T component by betatron acceleration and the resultant temperature anisotropy (T>T-vertical bar) formed led to the simultaneous generation of both EMIC (ion) and chorus (electron) waves. The EMIC waves had maximum wave amplitudes of approximate to 6nT in a approximate to 60nT ambient field B-0. The observed EMIC wave amplitudes were about approximate to 10 times higher than the usually observed chorus amplitudes (approximate to 0.1-0.5nT). The EMIC waves are found to be coherent to quasi-coherent in nature. Calculations of relativistic approximate to 1-2MeV electron pitch angle transport are made using the measured wave amplitudes and wave packet lengths. Wave coherency was assumed. Calculations show that in a approximate to 25-50ms interaction with an EMIC wave packet, relativistic electron can be transported approximate to 27 degrees in pitch. Assuming dipole magnetic field lines for a L = 9 case, the cyclotron resonant interaction is terminated approximate to 20 degrees away from the magnetic equator due to lack of resonance at higher latitudes. It is concluded that relativistic electron anomalous cyclotron resonant interactions with coherent EMIC waves near the equatorial plane is an excellent loss mechanism for these particles. It is also shown that E > 1MeV electrons cyclotron resonating with coherent chorus is an unlikely mechanism for relativistic microbursts. Temporal structures of approximate to 30keV precipitating protons will be approximate to 2-3s which will be measurable at the top of the ionosphere.