Proton/electron temperature ratio in the magnetotail

Abstract. We study the temperature ratio of protons and electrons based on statistics of Cluster observations in the Earth's magnetotail from 2001 to 2004. During these years, from June to November, the Cluster spacecraft visited the plasma sheet at the distance r~−19 R_E. We use proton and electron moments collected in the central region of the plasma sheet (|Z|<5 R_E). We find an average ratio of proton and electron temperatures ⟨T_p/T_e ⟩ ≈ 3.5. The dependence of T_p on T_e can be approximated by the power-law function: T_p ≈ 11T_e^0.62, where T_p and T_e are measured in MK. A previous reported ratio ⟨T_p/T_e ⟩ ~ 7 is limited to small electron temperatures <20 MK. The observations with the high electron temperature correspond to smaller values of the electron density and larger values of the proton and electron bulk velocities. A correlation between T_e and curlometer current density is not found.