Monte-Carlo simulations of ion velocity distributions and resulting incoherent radar spectra under strong ion frictional heating conditions

During periods where strong electric fields penetrate weakly ionized plasma at high latitudes the ion velocity distribution can differ enough from a Maxwellian shape to substantially change Incoherent Scatter Radar (ISR) spectra, and thus the analysis of those spectra. In this work an advanced description of the ion velocity distribution and spectra is found through improvements made to previous studies that employed Monte-Carlo simulations. These improvements include: 1) a higher resolution one-dimensional ion velocity distribution, 2) a new velocity distribution fitting technique, 3) the use of Nyquist diagrams to check the plasma stability, 4) a study of more recent published O⁺-O resonant charge exchange collision cross-sections, 5) the option to incorporate ion-ion and ion-electron collisions in the ion velocity distribution, and 6) an improved filtering technique to reduce statistical noise. Through these improvements, it has been found that: 1) ion-ion and ion-electron collisions have a minimal impact on the NO⁺ line-of-sight temperature, but a strong impact on the O⁺ temperature parallel to the magnetic field, 2) the choice of O⁺-O resonant charge exchange collision cross-section can change the ion temperature along a line-of-sight by several 1000 K under strong electric fields, as well as possibly drive a plasma to be stable, 3) NO⁺ spectra can generally be modeled using Maxwellian velocity distributions, and 4) O⁺ spectra parallel to the magnetic field show an apparent increase in electron temperature. This work is discussed in greater detail in this report, and will aid future studies into ion temperature anisotropy and ISR spectra.