Normal‐ and Reversed‐Boomerang Stripes on Electron Pitch Angle Distributions: Solar Wind Dynamic Pressure Effect
X. X. Zhao, Qiugang Zong, Jianjun Liu, Chao Yue, Xu‐Zhi Zhou, Yixin Hao, Xingran Chen, D. Yu. Klimushkin, A. V. Rubtsov, J. B. Blake, S. G. Claudepierre, G. D. Reeves
Abstract
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.