Estimating the Azimuthal Mode Structure of ULF Waves Based on Multiple GOES Satellite Observations
Estimating the Azimuthal Mode Structure of ULF Waves Based on Multiple GOES Satellite Observations
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DOI：
10.1029/2019ja026927
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发表时间：
2018-12
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影响因子：
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通讯作者：
M. Barani;W. Tu;T. Sarris;K. Pham;R. Redmon
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文献类型：
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作者：
M. Barani;W. Tu;T. Sarris;K. Pham;R. Redmon
表征超低频（ULF）波的方位角模式数m对于计算辐射带电子的径向扩散是必要的。交叉谱技术应用于多对GOES卫星观测到的压缩Pc5 ULF波，以估计2010年5月28日至31日风暴期间的方位角模式结构。我们发现，允许正和负的m是很重要的，以实现一个更现实的模式数分布，并解决波的传播方向。在风暴开始期间，当太阳风动压较高时，发现ULF波功率在低模数下占主导地位。中午前后，m的符号发生了有趣的变化，这与中午前后太阳风抖振驱动ULF波，产生反向日波传播是一致的。低模ULF波也被发现在磁局部时的全球覆盖范围比以前假设的要小。相反，在风暴主相和早期恢复阶段，当太阳风动压低，极光电急流指数高，波功率分布在所有的模式从低到高。发现高模波覆盖的磁局部时间范围比以前假设的更广。此外，为了减少2nπ的不确定性，解决了m，交叉对分析卫星现场测量的第一次，这被证明是有效的，在高极光电喷流期间产生更可靠的模式结构的超低频波。
Characterizing the azimuthal mode number, m, of ultralow‐frequency (ULF) waves is necessary for calculating radial diffusion of radiation belt electrons. A cross‐spectral technique is applied to the compressional Pc5 ULF waves observed by multiple pairs of GOES satellites to estimate the azimuthal mode structure during the 28‐31 May 2010 storm. We find that allowing for both positive and negative m is important to achieve a more realistic distribution of mode numbers and to resolve wave propagation direction. During the storm commencement when the solar wind dynamic pressure is high, ULF wave power is found to dominate at low‐mode numbers. An interesting change of sign in m occurred around noon, which is consistent with the driving of ULF waves by solar wind buffeting around noon, creating antisunward wave propagation. The low‐mode ULF waves are also found to have a less global coverage in magnetic local time than previously assumed. In contrast, during the storm main phase and early recovery phase when the solar wind dynamic pressure is low and the auroral electrojet index is high, wave power is shown to be distributed over all modes from low to high. The high‐mode waves are found to cover a wider range of magnetic local time than what was previously assumed. Furthermore, to reduce the 2nπ ambiguity in resolving m, a cross‐pair analysis is performed on satellite field measurements for the first time, which is demonstrated to be effective in generating more reliable mode structure of ULF waves during high auroral electrojet periods.