Effects of heavy ions on ULF wave resonances near the equatorial region

Abstract

[1] Pc1-2 ULF waves are strongly associated with the presence of various ions in the magnetosphere. We investigate the role of heavy ion resonances in nonuniform plasmas near the equatorial region. By adopting the invariant imbedding method, the coupled plasma wave equations are solved in an exact manner to calculate the resonant absorption at the ion-ion hybrid resonance. Our results show that irreversible mode conversion occurs at the resonance, which absorbs the fast wave energy. It is found that waves near the resonances appear with linear polarization, and their amplitude and frequency are sensitive to the properties of the heavy ion plasma composition. We examine how these resonances occur for various H + -He + populations in detail by performing an accurate calculation of the mode conversion efficiency. Because the multi-ion hybrid resonance locations in cold plasmas are determined by simple parameters, such as the fraction of the ion number density of each species and the magnetic field, we suggest that it is possible to monitor heavy ion composition by examining the peak frequencies of linearly polarized wave events in either electric field or magnetic field spectral data.

Mode Conversion of Waves in the Ion-Cyclotron Frequency Range in Magnetospheric Plasmas

“…In fusion plasmas, contamination with carbon impurities was shown to have profound consequences on the absorption efficiency of ion-cyclotronresonance heating and can be used for its optimization [1]. Waves in the ion-cyclotron range of frequencies, further referred to as ion-cyclotron waves, have been frequently observed and studied also in planetary magnetospheres.Observational studies indicate, in addition to protons, the presence of several ion species, e.g., He þ at Earth's, Na þ at Mercury's, and S 2þ and O þ at Jupiter's planetary environments [2]. The presence of multiple ion species, even with small concentrations, can lead to the appearance of new and modified resonance, cutoff, and crossover frequencies [3].…”

“…Observational studies indicate, in addition to protons, the presence of several ion species, e.g., He þ at Earth's, Na þ at Mercury's, and S 2þ and O þ at Jupiter's planetary environments [2]. The presence of multiple ion species, even with small concentrations, can lead to the appearance of new and modified resonance, cutoff, and crossover frequencies [3].…”

Temperature dependence of mode conversion in warm, unmagnetized plasmas with a linear density profile

“…33 In this paper, we restudy the temperature effect on the linear mode conversion between electromagnetic and Langmuir waves and calculate the mode conversion coefficients for the forward and backward mode conversion processes in a numerically accurate manner, using the invariant imbedding method developed previously by two of us. 14,15,28,[36][37][38][39][40][41][42][43][44] We verify that the principle of reciprocity for the forward and backward mode conversion coefficients holds precisely regardless of temperature and that the mode conversion peak shifts as the temperature increases. The detailed dependence of the mode conversion coefficient on temperature is different from those of previous results and is substantially stronger than the results of other studies.…”

Localization of Ultra-Low Frequency Waves in Multi-Ion Plasmas of the Planetary Magnetosphere

“…The inaccessibility occurs because FWs propagating from Na + -rich to H + -rich plasma directly encounter the IIH resonance location where strong energy absorption occurs (up to 100% as predicted by Lee et al 2008). For waves with ω/Ω H < 0.3, the FWs are partially absorbed at the IIH resonance location and the rest of the energy can reach the FW cutoff locations where n 2 || = ε L , and then encounter another IIH resonance location at X < 0.5.…”