A New N+ Band of Electromagnetic Ion Cyclotron Waves in Multi‐Ion Cold Plasmas

• Published in: Geophysical research letters 2018-10, Vol.45 (19), p.10,150-10,159
• Main Authors: Bashir, M. F., Ilie, R.
• Format: Article
• Language: English
• Subjects: Activation; cold plasma; Cold plasmas; Crossovers; Cyclotron frequency; Cyclotron resonance; Detection; Dispersion; Dynamics; EMIC waves; heavy ions; Ion cyclotron waves; Ions; Magnetosphere; Magnetospheres; minimum resonant energy; Missions; Motivation; N+ band; Nitrogen; Oxygen; Properties; Properties (attributes); Resolution; Wave spectra; Waves; wave‐particle interaction
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL080280

The dispersion relation for electromagnetic ion cyclotron (EMIC) waves is analyzed for a multi‐ion cold plasma. Several cases accounting for the relative contribution of the nitrogen (N+) and the oxygen (O+) ions and wave normal angle (θ) are presented. It is found that the presence of N+ significantly changes the dispersion properties of EMIC waves, leading to a new frequency band with additional cutoff, crossover, and resonance frequencies just above the oxygen cyclotron frequency ( ΩO+). The method for estimation of ions concentration from cutoff frequencies based on observation is also revisited, and N+ concentration is determined. The minimum resonant energy of N+ band is also calculated. This new N+ band is relevant to reduce the discrepancy in mode detection near ΩO+ in the observed wave spectrum in order to quantify the transport and energization of N+, in addition to O+, for their relative contribution to the loss and/or scattering mechanisms. Plain Language Summary EMIC waves are important due to their role in the dynamics of the magnetosphere. The theoretical prediction of a new N+ band in EMIC waves has been proposed, which has totally different dispersion properties than O+ band and can lead to motivation for finding the possible solution to refine data of current missions with such mass resolution to distinct N+ from O+. The observational evidence of low‐frequency N+ band EMIC waves of this theoretical finding may become possible after the mass resolution. In this letter, we demonstrate that the relative contribution of N+ to O+ introduces a new N+ band and significantly affects the dispersion properties of EMIC waves. Key Points Presence of N+ allows for the existence of a new N+ band close to ΩO+, which alters the dispersion characteristics of EMIC waves N+ ion concentration is evaluated from the observed wave characteristics, which suggests almost the same N+ and O+ composition This new band has the potential to address the discrepancy between He+ and O+ bands near the ΩO+ and advance understanding of EMIC wave