ULF Wave Activity in the Magnetosphere: Resolving Solar Wind Interdependencies to Identify Driving Mechanisms
ULF Wave Activity in the Magnetosphere: Resolving Solar Wind Interdependencies to Identify Driving Mechanisms
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DOI：
10.1002/2017ja024740
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发表时间：
2018-04
期刊：
影响因子：
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通讯作者：
S. Bentley;C. E. Watt;Mathew J. Owens;I. J. Rae
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文献类型：
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作者：
S. Bentley;C. E. Watt;Mathew J. Owens;I. J. Rae
磁层中的超低频波参与了辐射带粒子的通电和输运，并受到外部太阳风的强烈驱动。然而，太阳风参数的相互依赖性和太阳风-磁层耦合过程的多样性使得区分单个过程的影响和利用太阳风特性预测磁层波能变得困难。我们以单一代表性频率（2.5 mHz）和单一磁纬度（对应于L ~ 6.6RE）检查了15年的日间地面测量。我们从瞬时非衍生太阳风参数中确定对ULF波功率的相对贡献，考虑到它们的相互依赖性。对地面极低频波功率影响最大的参数是太阳风速度vsw、向南行星际磁场分量Bz<0和数密度扰动求和功率δNp。同时，从属参数Bz和δNp仍然占相当大的功率。我们认为这三个参数对应于开尔文-亥姆霍兹不稳定性、通量传递事件的形成和/或传播以及横扫地球的太阳风结构的密度扰动的驱动。我们预计，这一新的参数减少将有助于比较磁层扇区之间的超低功率产生机制，并将实现更复杂的经验模型，利用外部太阳风驱动参数预测磁层超低功率。
Ultralow frequency (ULF) waves in the magnetosphere are involved in the energization and transport of radiation belt particles and are strongly driven by the external solar wind. However, the interdependency of solar wind parameters and the variety of solar wind‐magnetosphere coupling processes make it difficult to distinguish the effect of individual processes and to predict magnetospheric wave power using solar wind properties. We examine 15 years of dayside ground‐based measurements at a single representative frequency (2.5 mHz) and a single magnetic latitude (corresponding to L ∼ 6.6RE). We determine the relative contribution to ULF wave power from instantaneous nonderived solar wind parameters, accounting for their interdependencies. The most influential parameters for ground‐based ULF wave power are solar wind speed vsw, southward interplanetary magnetic field component Bz<0, and summed power in number density perturbations δNp. Together, the subordinate parameters Bz and δNp still account for significant amounts of power. We suggest that these three parameters correspond to driving by the Kelvin‐Helmholtz instability, formation, and/or propagation of flux transfer events and density perturbations from solar wind structures sweeping past the Earth. We anticipate that this new parameter reduction will aid comparisons of ULF generation mechanisms between magnetospheric sectors and will enable more sophisticated empirical models predicting magnetospheric ULF power using external solar wind driving parameters.