The 2‐D Structure of Foreshock‐Driven Field Line Resonances Observed by THEMIS Satellite and Ground‐Based Imager Conjunctions
The 2‐D Structure of Foreshock‐Driven Field Line Resonances Observed by THEMIS Satellite and Ground‐Based Imager Conjunctions
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DOI：
10.1029/2019ja026668
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发表时间：
2019-08
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影响因子：
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通讯作者：
Boyi Wang;Y. Nishimura;Hui Zhang;X. Shen;L. Lyons;V. Angelopoulos;Y. Ebihara;A. Weatherwax;A. Gerrard;H. Frey
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文献类型：
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作者：
Boyi Wang;Y. Nishimura;Hui Zhang;X. Shen;L. Lyons;V. Angelopoulos;Y. Ebihara;A. Weatherwax;A. Gerrard;H. Frey
最近对Pc 5波段（150-600 s）超低频波的研究发现，前震扰动可以驱动昼侧压缩波和场线共振，这是昼侧磁层中两种典型的Pc 5波模式。然而，这是很难找到的向阳面Pc 5波的空间结构，使用少量的卫星或地面磁力计。这项研究确定了2008年6月29日在两个系列的Pc 5波期间，利用THEMIS卫星和南极全天空成像仪的协调观测，确定了日侧Pc 5波的二维结构及其驱动因素。这些Pc 5波被认为是场线共振（FLR）和驱动的前震扰动。在南极的地基全天空成像仪显示，周期性的极向移动弧与FLR同时发生在约3°纬度的卫星足迹附近，并具有与FLR相同的频率。这表明它们是FLR的极光特征。在二维图像中进一步确定了磁层中FLR的方位角分布及其在电离层中的南北宽度。在第一种情况下，FLR对称地分布在午前和午后区域，在赤道平面内具有异相振荡作为奇环形模式。在第二种情况下，350-500 s和300-450 s周期波的方位角波长在赤道平面上分别为~8.0和~5.2 Re。它还显示了嵌入大尺度弧中的精细方位结构，表明高方位波数（m ~ 140）模式波与低波数FLR耦合。
Recent studies of Pc5‐band (150–600 s) ultralow frequency waves found that foreshock disturbances can be a driver of dayside compressional waves and field line resonance, which are two typical Pc5 wave modes in the dayside magnetosphere. However, it is difficult to find spatial structure of dayside Pc5 waves using a small number of satellites or ground magnetometers. This study determines 2‐D structure of dayside Pc5 waves and their driver by utilizing coordinated observations by the THEMIS satellites and the all‐sky imager at South Pole during two series of Pc5 waves on 29 June 2008. These Pc5 waves were found to be field line resonances (FLRs) and driven by foreshock disturbances. The ground‐based all‐sky imager at South Pole shows that periodic poleward moving arcs occurred simultaneously with the FLRs near the satellite footprints over ~3° latitude and had the same frequencies as FLRs. This indicates that they are the auroral signature of the FLRs. The azimuthal distribution of the FLRs in the magnetosphere and their north‐south width in the ionosphere were further determined in the 2‐D images. In the first case, the FLRs distribute symmetrically in the prenoon and postnoon regions with out‐of‐phase oscillation as the odd toroidal mode in the equatorial plane. In the second case, the azimuthal wavelengths of the 350–500 s and 300–450 s period waves were ~8.0 and ~5.2 Re in the equatorial plane. It also shows a fine azimuthal structure embedded in the large‐scale arcs, indicating that a high azimuthal wave number (m ~ 140) mode wave coupled with the low‐wave number FLRs.