Normal‐ and Reversed‐Boomerang Stripes on Electron Pitch Angle Distributions: Solar Wind Dynamic Pressure Effect

Abstract

In the inner magnetosphere dominated by the dipole magnetic field, energetic electrons of 90° pitch angle drift faster than those of other pitch angles. Electron flux oscillations initiated by injections or drift resonances will be observed earlier at a 90° pitch angle, that is, 90°‐leading boomerang‐shaped stripes on pitch angle distributions(PADs) are expected. In this work, reversed‐boomerang stripes (90° observed last) are first reported from the observations of RBSP‐A at L‐shell ∼5.9 on 11 March 2016. The corresponding solar wind dynamic pressure is over 10 nPa, which suggests that strong compression on the magnetosphere changes the magnetic field and drift frequencies of energetic electrons. Test particles running in an image‐dipole magnetic field (off‐equatorial minima exists at dayside large L‐shell) reproduce the abnormal (90° slower) drift velocities at L‐shell >5.8 but are normal at L‐shell <4.5 dominated by a dipole field. Normal boomerang stripes on PADs are indeed observed by RBSP‐B at L‐shell ∼4.0, indicating the solar wind dynamic pressure effect.

Plasmasphere Control of ULF Wave Distribution at Different Geomagnetic Conditions

“…Figure 5c shows 〈 f wave 〉 distribution during disturbed time, with two clearly separated regions: low frequency Pc5 waves at MLT = 05–12 hr and high frequency Pc4 waves at MLT = 18–05 hr. The former waves' low frequency is consistent with some direct excitation from the SW, for example, pressure pulse (Zhao et al., 2022), but one may expect externally driven waves to be clear in both disturbed and quiet time. The latter, high frequency, waves correspond to storm‐time pulsations, but usually such waves fall into the Pc5 band (Anderson et al., 1990; Takahashi & Anderson, 1992).…”

Ion Acceleration and Corresponding Bounce Echoes Induced by Electric Field Impulses: MMS Observations

“…Li, Liu, Zong, Zhou, Hao, Pollock, et al., 2021, Li, Yue, et al., 2022; Y.‐X. Li, Yue, et al., 2022; X. X. Zhao et al., 2022). Due to the close relation with particle transport, sudden variations of particle fluxes in spacecraft observations have garnered considerable attention.…”

Relativistic Electron Precipitation Events Driven by Solar Wind Impact on the Earth's Magnetosphere

“…The impact of the strongly intensified solar wind dynamic pressure that is characteristic to large‐scale solar wind transients (sometimes seen as distinct pulses of augmented pressure) compresses the Earth's dayside magnetosphere and has an immediate influence on charged particle dynamics. This includes the formation of unstable (anisotropic) particle velocity distributions (e.g., X. X. Zhao et al., 2022, and references therein) as well as electron flux dropouts and enhancements (e.g., Da Silva et al., 2023; X. H. Ma et al., 2021). The basic mechanism for the formation of unstable particle distributions consists of the adiabatic heating of ions and electrons via induction electric fields.…”