Lower Hybrid Drift Waves as a Driver of Turbulent Reconnection in Earth’s Magnetotail

Recent observations by the Magnetospheric Multiscale (MMS) mission have shown that magnetic reconnection in Earth’s magnetotail can exhibit turbulent behavior [1]. These studies also reveal a strong correlation between the level of turbulence and local plasma density: fluctuations in both electric and magnetic fields become pronounced when the density drops to ~0.1 cm⁻³ [1]. To further investigate the mechanisms driving turbulence during reconnection, we analyze additional events from July 2017, including one featuring an electron diffusion region (EDR) crossing [2]. Our analysis shows that strong electric and magnetic field fluctuations are consistently observed when the perpendicular electron flow velocity is large, which is the free energy for the excitation of lower hybrid drift waves (LHDWs) [3]. The low-density environment amplifies the local electron flow velocity and reduces the electron beta, creating conditions favorable for LHDW instability and potentially triggering the observed turbulence. The stability of LHDWs under these local conditions has been further examined using special linear theory for space plasmas with non-Maxwellian electron distribution functions.

[1] R. Ergun et al., Astrophys. J. 898, 154, (2020).

[2] L. Chen et al., Phys. Rev. Lett. 125, 025103 (2020).

[3] J. Yoo et al., Geophys. Res. Lett. 47 (2020).