ULF‐Modulation of Whistler‐Mode Waves in the Inner Magnetosphere During Solar Wind Compression

Abstract

The solar wind plays important roles in terrestrial magnetosphere dynamics, including the particle population and plasma wave generation. Here, we report an interesting event that ultralow frequency (ULF) waves are enhanced right after solar wind compression and the compressional mode ULF wave subsequently modulates both the intensity and energy flux direction of whistler‐mode waves. Quasi‐periodic whistler‐mode wave packets are observed around L = 5.6 at noon sector by Van Allen Probes. Growth rate calculation demonstrates that the compressional mode ULF wave can modulate the whistler‐mode wave intensity by modulating the energetic electron anisotropy. Moreover, the direction of wave energy flux is observed to alternate between northward and southward at equator, which is probably because the intense ULF waves periodically alter the relative direction of the wave source region with respect to the spacecraft. The current results provide a chain of observational evidences to illustrate how the generation and propagation of whistler‐mode waves in the inner magnetosphere are affected by ULF waves during the solar wind dynamic pressure enhancement.

Nonlinear Wave Growth Analysis of Chorus Emissions Modulated by ULF Waves

“…In fact, the observed modulation of the chorus waves by ULF compressional waves was interpreted in Shang et al. (2021) as the chorus wave source region being modified by the north/south oscillations of the magnetic flux tubes.…”

“…Therefore, the excitation of the chorus waves may be modulated by the large-scale ULF waves via regulating the background field configurations. In fact, the observed modulation of the chorus waves by ULF compressional waves was interpreted in Shang et al (2021) as the chorus wave source region being modified by the north/south oscillations of the magnetic flux tubes.…”

ULF Wave Modeling, Effects, and Applications: Accomplishments, Recent Advances, and Future

“…ULF waves can also modulate higher-frequency, EMIC and VLF wave growth (e.g., Li et al, 2011;Gamayunov and Engebretson, 2021;Shang et al, 2021), transferring energy from large to small scales. Concerning EMIC waves, the pioneering work by Lyons and Thorne (1972) demonstrated that these waves can play a critical role in the dynamics of multi-MeV electrons.…”

Frequency‐Dependent Responses of Plasmaspheric Hiss to the Impact of an Interplanetary Shock

“…Previous studies suggest that the whistler‐mode chorus waves are generally intensified (Fu, Cao, Mozer, et al., 2012; Fu, Cao, Zong, et al., 2012), while the intensity of plasmaspheric hiss waves decreases in the dayside and increases in the nightside (Liu, Su, Gao, Reeves, et al., 2017; Su et al., 2015; Yue et al., 2017) after the IP shock arrival. More recent studies indicate that plasmaspheric hiss waves also show patchy or modulated patterns under disturbed solar wind conditions or IP shock arrival (Chakraborty et al., 2021; Liu et al., 2019; Shang et al., 2021).…”