INTERACTION OF RING CURRENT AND RADIATION BELT PROTONS WITH DUCTED PLASMASPHERIC HISS .2. TIME EVOLUTION OF THE DISTRIBUTION FUNCTION

The evolution of the bounce-averaged ring current/radiation belt proto n distribution is simulated during resonant interactions with ducted p lasmaspheric hiss. The plasmaspheric hiss is assumed to be generated b y ring current electrons and to be damped by the energetic protons. Th us energy is transferred between energetic electrons and protons using the plasmaspheric hiss as a mediary. The problem is not solved self-c onsistently. During the simulation period, interactions with ring curr ent electrons (not represented in the model) are assumed to maintain t he wave amplitudes in the presence of damping by the energetic protons , allowing the wave spectrum to be held fixed. Diffusion coefficients in pitch angle, cross pitch angle/energy, and energy were previously c alculated by Kozyra et al. (1994) and are adopted for the present stud y. The simulation treats the energy range, E greater than or equal to 80 keV, within which the wave diffusion operates on a shorter timescal e than other proton loss processes (i.e., Coulomb drag and charge exch ange). These other loss processes are not included in the simulation. An interesting result of the simulation is that energy diffusion maxim izes at moderate pitch angles near the edge of the atmospheric loss co ne. Over the simulation period, diffusion in energy creates an order o f magnitude enhancement in the bounce-averaged proton distribution fun ction at moderate pitch angles. The loss cone is nearly empty because scattering of particles at small pitch angles is weak. The bounce-aver aged flux distribution, mapped to ionospheric heights, results in elev ated locally mirroring proton fluxes. OGO 5 observed order of magnitud e enhancements in locally mirroring energetic protons at altitudes bet ween 350 and 1300 km and invariant latitudes between 50 degrees and 60 degrees (Lundblad and Soraas, 1978). The proton distributions were hi ghly anisotropic in pitch angle with nearly empty loss cones. The simi larity between the observed distributions and those resulting from thi s simulation raises the possibility that interactions with plasmaspher ic hiss play a role in forming and maintaining the characteristic zone s of anisotropic proton precipitation in the subauroral ionosphere. Fu rther assessment of the importance of this process depends on knowledg e of the distribution in space and time of ducted plasmaspheric hiss i n the inner magnetosphere.