Determining the Temporal and Spatial Coherence of Plasmaspheric Hiss Waves in the Magnetosphere

Abstract

Plasmaspheric hiss is one of the most important plasma waves in the Earth's magnetosphere to contribute to radiation belt dynamics by pitch‐angle scattering energetic electrons via wave‐particle interactions. There is growing evidence that the temporal and spatial variability of wave‐particle interactions are important factors in the construction of diffusion‐based models of the radiation belts. Hiss amplitudes are thought to be coherent across large distances and on long timescales inside the plasmapause, which means that hiss can act on radiation belt electrons throughout their drift trajectories for many hours. In this study, we investigate both the spatial and temporal coherence of plasmaspheric hiss between the two Van Allen Probes from November 2012 to July 2019. We find ∼3,264 events where we can determine the correlation of wave amplitudes as a function of both spatial distance and time lag in order to study the spatial and temporal coherence of plasmaspheric hiss. The statistical results show that both the spatial and temporal correlation of plasmaspheric hiss decrease with increasing L‐shell, and become incoherent at L > ∼4.5. Inside of L = ∼4.5, we find that hiss is coherent to within a spatial extent of up to ∼1,500 km and a time lag up to ∼10 min. We find that the spatial and temporal coherence of plasmaspheric hiss does not depend strongly on the geomagnetic index (AL*) or magnetic local time. We discuss the ramifications of our results with relevance to understanding the global characteristics of plasmaspheric hiss waves and their role in radiation belt dynamics.

Determining the Global Scale Size of Chorus Waves in the Magnetosphere

“…Agapitov et al (2018) obtained that the correlation of chorus amplitudes drops to 0.5 near 250 < Δr < 800 km using five THEMIS spacecraft observations, which is also consistent with our result. Moreover, it can be seen that the spatial scale size of chorus wave is significantly smaller than that of plasmaspheric hiss (∼1,500 km) shown by Zhang et al (2021). This is consistent with the traditional concept that the hiss waves are more uniform than the chorus waves.…”

“…We use a similar method to Zhang et al. (2021), which studied the spatial and temporal scale size of plasmaspheric hiss wave, to analyze chorus waves. First, we analyze the distribution of locations and satellite separations for all 3,875 events.…”

“…For the plasmaspheric hiss waves, Zhang et al. (2021) has statistically studied the spatial and temporal scale size of plasmaspheric hiss by analyzing the correlation between the wave amplitudes detected by the two Van Allan Probes. They found the plasmaspheric hiss waves are statistically incoherent when spatial separation larger than ∼1,500 km or temporal separation larger than ∼10 min at L < 4.5, while it is always incoherent at L > 4.5.…”

“…Zhang et al. (2021) therefore concluded that the plasmaspheric hiss could be more variable than previously thought, and the statistical averages for the models of drift‐averaged diffusion should be constructed with care. For the magnetospheric chorus waves, Santolík, Gurnett et al.…”

“…In this paper, similar to the analysis of hiss waves by Zhang et al (2021), we study the temporal and spatial variability of chorus waves using two Van Allen Probes, which provide an ideal platform for this analysis through the constantly changing distance from ∼0.01 to 5 R E , with probe A lapping probe B every several weeks. To be special, we statistically study the correlation of chorus wave amplitudes detected by two satellites against the satellite time lag and separation to identify the spatial and temporal variation scale of wave characteristics.…”