Dependencies of high-latitude plasma convection: Consideration of interplanetary magnetic field, seasonal, and universal time factors in statistical patterns
Dependencies of high-latitude plasma convection: Consideration of interplanetary magnetic field, seasonal, and universal time factors in statistical patterns
复制标题
DOI：
10.1029/2004ja010815
复制
发表时间：
2005-09
影响因子：
--
通讯作者：
J. Ruohoniemi;R. Greenwald
中科院分区：
文献类型：
--
作者：
J. Ruohoniemi;R. Greenwald
[1]分析了北半球超级双极光雷达网(SuperDARN)九部雷达的数据库，以获取有关影响高纬度电离层等离子体对流的因素的信息。这些速度测量是在1998-2002年间收集的。首先利用这些资料导出了一个新的对流统计模式，该模式改进了Ruohoniemi和Greenwald(1996)早期的单雷达模式，该模式描述了对流模式与GSM Y-Z平面上IMF的大小和方向的关系。然后，我们得出了按季节、年份和雷达进行二次分类的平均模式。通过对比by+和−的结果，可以最清楚地看到出现的这种依赖关系。对流型的季节效应与BY的季节效应有相似之处。特别是，按+/夏季(按−/冬季)的组合加强了按符号因子的趋势，即将黄昏和黎明的细胞雕刻成更圆/新月(新月/圆形)的形状，并将新月细胞移动到子午线上。然而，这些组合与总交叉极帽电位下降ΦPC的较低估计有关，而非强化组合会导致ΦPC升高，特别是在−/夏季。从冬季到夏季，ΦPc总体呈上升趋势，尽管纯季节对潜势下降的影响弱于−符号/季节因子。我们没有发现5个独立年份的模式之间有明显的差异，这些模式跨越了最近的太阳周最大值间隔。通过雷达分类，我们发现By+的模式之间几乎没有差异，但−的模式出现了变化，这可能与世界时(UT)的依赖一致。因此，季节和UT对高纬电离层对流的影响取决于IMF，尤其是BY的标志。我们推测在−条件下，电离层电导率的变化对磁层-电离层耦合的影响更大。
[1] The database of the nine radars of the Super Dual Auroral Radar Network (SuperDARN) in the northern hemisphere has been analyzed for information on factors that influence the convection of plasma in the high-latitude ionosphere. The velocity measurements were collected over the period 1998–2002. The data were first used to derive a new statistical model of convection that improves upon the earlier one-radar model of Ruohoniemi and Greenwald (1996) in its specification of the dependence of the convection pattern on the magnitude and direction of the IMF in the GSM Y-Z plane. We then derived average patterns for secondary sortings by season, year, and radar. Such dependencies as emerged were most clearly seen by contrasting the results for By+ and By−. The seasonal effect in the convection pattern is found to have similarities to that of the sign of By. In particular, the combination of By+/summer (By−/winter) reinforces the tendency of the By sign factor to sculpt the dusk and dawn cells into more round/crescent (crescent/round) shapes and to shift the crescent cell across the midnight MLT meridian. However, these combinations are associated with lower estimates of the total cross polar cap potential drop, ΦPC, while the nonreinforcing combinations produce elevated ΦPC, especially By−/summer. There is an overall tendency for ΦPC to increase from winter to summer, although the pure seasonal effect on the potential drop is weaker than that of the By−sign/season factor. We did not find pronounced differences among the patterns derived for the 5 individual years, which spanned the most recent interval of solar cycle maximum. Sorting by radar, we found few differences among the patterns for By+, but for By−, variations emerged that are consistent with a possible dependence on universal time (UT). The impacts of season and UT on convection in the high-latitude ionosphere thus depends on the IMF, especially the sign of By. We speculate that variability in the ionospheric conductivity has a greater effect on magnetosphere-ionosphere coupling under By− conditions.