Determining the Global Scale Size of Chorus Waves in the Magnetosphere

Abstract

Chorus waves outside the plasmapause influence the Earth's radiation belt dynamics by interacting with energetic electrons via cyclotron and Landau resonance. Recent numerical diffusion experiments indicate that the diffusion process is sensitive to the spatial and temporal scale of variability in the wave‐particle interaction, which is reported to be more efficient than that based on the traditional average model. Using Van Allen Probes A and B data from November 2012 to July 2019, the spatial and temporal scale size of chorus waves are calculated by the correlation between the wave amplitudes detected by two satellites with varying spatial separation or time lag. We found that, the chorus wave is incoherent when the spatial extent is greater than 433 km or the time lag lasts ∼10 s, which are significantly smaller than that of plasmaspheric hiss. In addition, the spatial correlations of chorus tend to be higher near noon or with lower geomagnetic activity. The temporal correlations of chorus are always statistically near zero, which are not influenced by the location and geomagnetic activity. Our results can help refine the model of the interactions between energetic particles and chorus waves in the radiation belt.

Whistler‐Mode Waves Inside Short Large‐Amplitude Magnetic Field Structures: Characteristics and Generation Mechanisms

“… $$$\langle f\rangle =\frac{\int \nolimits_{0.1{f}_{ce}}^{{f}_{ce}}{B}_{w}^{2}(f)fdf}{\int \nolimits_{0.1{f}_{ce}}^{{f}_{ce}}{B}_{w}^{2}(f)df}$$$ $$${\increment}f=\sqrt{\frac{\int \nolimits_{0.1{f}_{ce}}^{{f}_{ce}}{B}_{w}^{2}(f){(f-\langle f\rangle )}^{2}df}{\int \nolimits_{0.1{f}_{ce}}^{{f}_{ce}}{B}_{w}^{2}(f)df}}$$$ $$${\boldsymbol{B}}_{\boldsymbol{w}}=\sqrt{\int \nolimits_{0.1{f}_{ce}}^{{f}_{ce}}{B}_{w}^{2}(f)df}$$$ f ce is the electron cyclotron frequency. Whistler‐mode waves (red dots in Figure 1h), following previous criteria (polarization >0.5, planarity >0.6, and ellipticity >0.7 near the average frequency, Li et al., 2014; S. Zhang et al., 2021), are identified by wave polarization analysis in Figures 1e–1g. These criteria are chosen to ensure that there is less wave power outside the polarization plane (planarity >0.6) and that the observed waves are right‐handed circularly polarized (polarization >0.5 and ellipticity >0.7).…”

“…f ce is the electron cyclotron frequency. Whistler-mode waves (red dots in Figure 1h), following previous criteria (polarization >0.5, planarity >0.6, and ellipticity >0.7 near the average frequency, Li et al, 2014;S. Zhang et al, 2021), are identified by wave polarization analysis in Figures 1e-1g.…”

Propagation of Very Oblique Chorus Waves Near a Plasmaspheric Plume Boundary

“…In this study, we assume the observed change of wave vector directions near the plume boundary is a spatial structure instead of a temporal structure, and that the wave sources in Figure 4 are uniformly distributed along the azimuthal direction. However, these assumptions may be undermined, as the observation time scale in our study, spanning 4 min, and the presumed spatial scale of wave sources, estimated at 2,500 km, considerably exceed the typical coherent chorus wave scales, which are around 10 s and 433 km, respectively (Zhang et al, 2021). Future studies might benefit from backward ray tracing, which can avoid these assumptions and pinpoint the source locations (Santolík et al, 2006).…”

Effects of Plasma Density on the Spatial and Temporal Scale Sizes of Plasmaspheric Hiss

“…The temporal scale of hiss wave represents the time of a hiss wave activity region exists at a particular location. As the direct factors in determining the spatial and temporal scale sizes, the spatial correlation was calculated by correlating the time series of integrated wave amplitudes observed by the two satellites without a time lag, while the temporal correlation was evaluated by correlating the time series of integrated wave amplitudes observed by the two satellites at the same location but at different times with a time lag (Zhang et al., 2021a, 2021b). The subsequent statistical analysis of 3,264 hiss wave events in Zhang et al.…”

“…Since chorus waves penetrating into the plasmasphere at high latitudes are the recognized “embryonic source” of hiss generation (Bortnik et al., 2008), the spatial and temporal scales of chorus wave power should be a determinant of the spatial and temporal scales of plasmaspheric hiss. However, the spatial and temporal scales of chorus waves are about a few hundred kilometers and 10 seconds (e.g., Agapitov et al., 2018; Agapitov et al., 2021; Zhang et al., 2021b), which are much smaller than that of plasmaspheric hiss. Therefore, there should be other factors influencing the spatial and temporal scales of hiss during the penetration of chorus wave power into the plasmasphere and the subsequent development of plasmaspheric hiss.…”