Proton and electron heating by radially propagating fast magnetosonic waves

We investigate the propagation, growth, and decay of fast magnetosonic wave s in the Earth's magnetosphere which are believed to contribute to proton h eating up to energies of a few hundred eV near the magnetic equator. We con struct a model of the proton and electron distribution functions from space craft data and use the HOTRAY code to calculate the path-integrated growth and decay of the waves over a range of L shells from L = 2 to L = 7. instab ility calculations show that the waves are excited at very large angles of propagation with respect to the magnetic field, psi approximate to 89 degre es, at the harmonics of the proton gyrofrequency Omega (H+) up to the lower hybrid resonance frequency omega (LHR) by a proton ring distribution at en ergies of the order of 10 keV. As a "rule of thumb", we find that growth is possible for omega > 30 Omega (H+) when the ring velocity exceeds the Alfv en speed nu (R) > nu (A), and for omega < 30<Omega>(H+) when nu (R) > 2 nu (A) For propagation in the meridian plane, waves generated just outside the plasmapause grow with large amplification as they propagate away from the Earth but eventually lose energy to plasma sheet electrons at energies of a few keV by Landau damping. The waves grow to large amplification at freque ncies just below omega (LHR) For inward propagation we find that waves gene rated just outside the plasmapause can propagate to L approximate to 2 with very little attenuation, suggesting that waves observed well inside the pl asmasphere could originate from a source region just outside the plasmapaus e. Strong wave growth only occurs for large angles of propagation, and thus the waves are confined to within a few degrees of the magnetic equator. Wa ves generated near geostationary orbit and which propagate toward the Earth are absorbed by Doppler-shifted cyclotron resonance when they propagate in to a region where nu (R) < <nu>(A). Cyclotron resonant absorption causes pi tch angle scattering and heating transverse to the ambient magnetic held. T he amount of absorption, and hence transverse proton heating, increases sig nificantly as the thermal proton temperature is increased up to 100 eV, sug gesting a feedback process. Ray tracing shows that transverse heating of th e thermal proton distribution is most likely to occur just outside the plas mapause where nu (A) is large. Since proton ring distributions are formed d uring magnetic storms at ring current energies, we suggest that fast magnet osonic waves provide an additional energy loss process for ring current dec ay.