Global view of the E region irregularity and convection velocities in the high‐latitude Southern Hemisphere

• Published in: Journal of geophysical research. Space physics 2017-02, Vol.122 (2), p.2467-2483
• Main Authors: Forsythe, Victoriya V., Makarevich, Roman A.
• Format: Article
• Language: English
• Subjects: Asymmetry; Bias; Convection; Density gradients; E region; Echoes; Farley‐Buneman; Geophysics; high‐latitude; Instability; Interplanetary magnetic field; Irregularities; Latitude; Magnetic fields; Plasma; Plasma convection; plasma irregularities; Plasmas (physics); Polarity; Radar networks; South Pole; Southern Hemisphere; Stability; SuperDARN; Velocity; Velocity distribution
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2016JA023711

Occurrence of the E region plasma irregularities is investigated using two Super Dual Auroral Radar Network (SuperDARN) South Pole (SPS) and Zhongshan (ZHO) radars that sample the same magnetic latitude deep within the high‐latitude plasma convection pattern but from two opposite directions. It is shown that the SPS and ZHO velocity distributions and their variations with the magnetic local time are different, with each distribution being asymmetric; i.e., a particular velocity polarity is predominant. This asymmetry in the E region velocity distribution is associated with the bump‐on‐tail of the distribution near the nominal ion acoustic speed Cs that is most likely due to the Farley‐Buneman instability (FBI) echoes or an inflection point of the distribution below nominal Cs that is most likely due to the gradient drift instability echoes. In contrast, the distribution of the convection velocity component was found to be symmetric, i.e., with no bump‐on‐tail or an inflection point, but with a bias (i.e., uniform shift) toward a particular polarity. It is demonstrated that the asymmetry in the convection pattern between the eastward and westward zonal components is unexpectedly strong, with the westward zonal component being predominant, especially at lower latitudes, while also exhibiting a strong interplanetary magnetic field By dependence. The observations are consistent with the notion that the asymmetry in the E region velocity distribution is highly sensitive to the bias in the convection component caused by the zonal convection component asymmetry and that the bump‐on‐tail or inflection point features may also depend on the irregularity height and the presence of strong density gradients modifying the FBI threshold value. Key Points E region irregularity velocity distribution is asymmetric due to the presence of waves generated by the Farley‐Buneman instability (FBI) High‐latitude plasma convection velocity distribution exhibits a bias in the zonal component that is dependent on magnetic latitude and IMF E region velocity distribution is highly sensitive to small changes in the plasma convection bias consistent with a lowered FBI threshold