Global view of the E region irregularity and convection velocities in the high‐latitude Southern Hemisphere
Global view of the E region irregularity and convection velocities in the high‐latitude Southern Hemisphere
复制标题
南半球高纬度E区不规则性与对流速度的全球视野
DOI：
--
复制
发表时间：
2017
期刊：
影响因子：
--
通讯作者：
R. Makarevich
中科院分区：
文献类型：
--
作者：
V. Forsythe;R. Makarevich
使用两个超级双极光雷达网络（SuperDARN）南极（SPS）和中山（ZHO）雷达研究了E区域等离子体不规则性的发生，这些雷达在高纬度等离子体对流模式内的相同磁纬度深处进行采样，但从两个相反的方向。结果表明，SPS和ZHO速度分布及其随磁局部时的变化是不同的，每种分布都是不对称的，即，特定的速度极性是主要的。E区速度分布中的这种不对称性与标称离子声速Cs附近的分布的尾部碰撞（bump-on-tail）相关联，其最有可能是由于法利-布尼曼不稳定性（FBI）回波，或者与标称Cs以下的分布的拐点相关联，其最有可能是由于梯度漂移不稳定性回波。相反，发现对流速度分量的分布是对称的，即，没有尾部碰撞或拐点，但有偏差（即，均匀移位）朝向特定极性。结果表明，东、向西纬向分量对流模式的不对称性出乎意料地强，尤其是在低纬度地区，向西纬向分量占主导地位，同时也表现出强烈的行星际磁场依赖性。观测结果与以下概念一致：E区速度分布的不对称性对纬向对流分量不对称性引起的对流分量偏差高度敏感，尾部碰撞或拐点特征也可能取决于不规则高度和存在强密度梯度，从而修改FBI阈值。
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.