Contribution of Ion Velocity Shears in the Direct Generation of Small-Scale Irregularities in the High-Latitude F Region
Contribution of Ion Velocity Shears in the Direct Generation of Small-Scale Irregularities in the High-Latitude F Region
French Title: Contribution des cisaillements de vitesses ioniques dans la génération directe d'irrégularités à petite échelle au sein de la région F de l'ionosphère à hautes latitudes
Previously Published Material: Part of this research was presented at the DASP meeting in February 2014. These results have not been published yet.
Abstract ID#: 33932
English Abstract:
Plasma instabilities play an important role in producing small-scale irregularities in the ionosphere. In particular, current-driven electrostatic ion-acoustic (CDEIA) instabilities contribute to high-latitude F-region electrodynamics. CDEIA instabilities are affected by ion velocity shears. Ion velocity shears are observed near auroral arc edges, sometimes coexisting with thermal ion upflow processes and field-aligned currents (FAC). The detection of naturally enhanced ion-acoustic lines (NEIALs) near the edges of auroral structures, often linked with ion upflows and parallel FACs, suggests that shear-modified CDEIA instabilities could take place in these regions. These observations led us to investigate whether these shears could enhance the incoherent scattering from CDEIA waves in the high-latitude F-region. We studied the effects of ion velocity shears on the theoretical incoherent scatter radar (ISR) spectrum density function (SDF) for stable plasmas. We found that, under the right conditions, small shears produce significant enhancements in ISR spectra, especially for directions near perpendicular to the geomagnetic field. This could lead to overestimations in the interpreted electron to ion temperature ratio and electron density when using standard ISR fitting procedures.