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Abstract:
Electron pitch angle distributions (PADs) are very important to understand dynamics in the Earth's magnetosphere. Using observations of the Magnetospheric Multiscale (MMS) mission, we statistically investigate the characteristics of several types of electron PADs with energies of 200 eV to 2 keV (low energy) and 2–30 keV (energetic energy) inside the dayside magnetopause (L = 8 ∼ 13). For the low (energetic) energy level, the occurrence rates of pancake, flat‐top, butterfly, isotropy, cigar, and rolling‐pin distributions are as follows: 50.34% (45.20%), 17.92% (43.41%), 3.07% (7.28%), 4.34% (1.54%), 16.20% (1.20%), and 1.80% (0.06%), respectively. The pancake PAD is mainly located at lower L‐shells with a maximum rate near the noonside, but other types of electron PADs occur at higher L‐shells. In addition, the occurrence rate of the flat‐top PAD is nearly the same for different magnetic local time. The butterfly and rolling‐pin PADs occur in the afternoon side. The cigar PAD is mostly located in both the dawnside and duskside but is very scarce in the noonside. Furthermore, the relationships between these PADs and the solar wind dynamic pressure (Pdyn) are studied. For low‐energy electrons, the occurrence rate of the pancake distribution decreases, and that of the butterfly distribution increases with the enhancement of Pdyn. However, for energetic energy level, the occurrence rate of the pancake (butterfly) PAD does not clearly decrease (increase) with the enhancement of Pdyn at L ≤ 12. The statistical results reveal the important role of Pdyn in electron dynamics inside the magnetopause.
