Velocity and Magnetic Fluctuations Across Machine Learning Defined Regions of the Magnetotail Plasma Sheet

Abstract We present a comprehensive analysis of magnetic and velocity fluctuations in Earth's magnetotail plasma sheet based on observations from the Magnetospheric Multiscale (MMS) mission during its 2017 magnetotail campaign. Utilizing a novel Hybrid Filter–Decision Tree Model (HFDTM), we systematically classify the plasma sheet ( X < −10 R_E in Geocentric Solar Ecliptic coordinates) into four key regions: the current sheet (CS), central plasma sheet (CPS), plasma sheet boundary layer (PSBL), and tail lobe. Within each region, we examine fluctuation dynamics across three critical flow regimes, including stagnant ( V < 50 km s −1 ), sub‐Alfvénic (50 km s −1 ≤ V < V A ), and super‐Alfvénic ( V ≥ V A ). Our key findings reveal: (a) Anisotropy Transition: Magnetic field anisotropy reverses with increasing flow speed, shifting from near‐isotropic values (Δ B ∥ /Δ B ⊥ ≈ 1.1) under stagnant conditions to strongly perpendicular‐dominated distributions (∼0.4) in the super‐Alfvénic regime; (b) Multimodal Heating: Multi‐peak structures in the thermal energy (E T ) spectrum, along with the co‐evolution of thermal (H T ) and kinetic (H V ) enstrophy from the CS to the PSBL, reveal a dual‐pathway heating mechanism involving both kinetic and magnetic energy transfer; and (c) Correlation Structure: Across all regions and regimes, weak‐to‐moderate velocity–magnetic field correlations dominate, with enhanced V ∥ ‐ B ∥ correlations under super‐Alfvénic flows. Collectively, these results identify the plasma sheet as a distinct turbulent regime, governed by localized energization mechanisms (e.g., reconnection, substorm dipolarization, and flow braking), marking a departure from the Alfvénic turbulence paradigm observed in the solar wind.