Lower Hybrid Drift Waves During Guide Field Reconnection

Abstract

Generation and propagation of lower hybrid drift wave (LHDW) near the electron diffusion region (EDR) during guide field reconnection at the magnetopause is studied with data from the Magnetospheric Multiscale mission and a theoretical model. Inside the current sheet, the electron beta (β e) determines which type of LHDW is excited. Inside the EDR, where the electron beta is high (β e ∼ 5), the long-wavelength electromagnetic LHDW is observed propagating obliquely to the local magnetic field. In contrast, the short-wavelength electrostatic LHDW, propagating nearly perpendicular to the magnetic field, is observed slightly away from the EDR, where β e is small (∼0.6). These observed LHDW features are explained by a local theoretical model, including effects from the electron temperature anisotropy, finite electron heat flux, electrostatics, and parallel current. The short-wavelength LHDW is capable of generating significant drag force between electrons and ions. Plain Language Summary The lower hybrid drift wave (LHDW) is generated inside the current sheet by the electric current perpendicular to the local magnetic field. With data from the Magnetospheric Multiscale (MMS) mission, we confirm that two types of LHDW are excited in the current sheet during magnetic reconnection with guide field, depending on the local plasma parameter, called beta (ratio between the magnetic field pressure and plasma pressure). One is the short-wavelength, quasi-electrostatic LHDW excited just outside the central reconnection site, called the electron diffusion region. The other is the long-wavelength, electromagnetic LHDW excited in the electron diffusion region. A local theoretical model is developed to explain the excitation of both types of the LHDW in the current sheet. Results from the model agree with MMS observations. The short-wavelength LHDW is capable of generating additional friction between electrons and ions, indicating possible importance of this LHDW on reconnection and electron dynamics.

Direct Observations of Electron Firehose Fluctuations in the Magnetic Reconnection Outflow

“…To further corroborate our results, we make sure that the fluctuations that we have identified as the EF waves are not the electromagnetic lower hybrid mode, which has been reported in several studies investigating magnetic reconnection in the Earth's magnetotail and at the magnetopause (Chen et al., 2020; Cozzani et al., 2021; Wang et al., 2022; Yoo et al., 2020). This further check is motivated by the fact that the observations are complex and characterized by significant uncertainties.…”

Electron acceleration driven by the lower-hybrid-drift instability

“…In these two regions, LHW are commonly observed in the vicinity of magnetic reconnection sites where strong density gradients do form. Their role on the onset (or relaxation) of magnetic reconnection has been addressed in the past and still represents a key point in the context of reconnection research (Daughton 2003;Lapenta et al 2003Lapenta et al , 2018Yoo et al 2020).…”

Magnetospheric Multiscale Mission Observations of Lower-hybrid Drift Waves in Terrestrial Magnetotail Reconnection with Moderate Guide Field and Asymmetric Plasma Density

“…The guide field can also reduce the reconnection rate, the electron nongyrotropic effects, and the thickness of the electron diffusion region (EDR; Yamada et al 2010). In addition, both asymmetries and the guide field have influence on the distributions and properties of plasma waves that play crucial roles in reconnection (Graham et al 2016(Graham et al , 2017Le et al 2018;Wilder et al 2019;Yoo et al 2020), such as whistler waves and lowerhybrid drift waves (LHDWs).…”

“…Besides, the LHDWs can be also induced by the modified two-stream instability (Graham et al 2017(Graham et al , 2019. The short-wavelength mode with k ⊥ ρ e ∼ 1 often develops at the current sheet boundary, while the longwavelength mode with k ⊥ (ρ i ρ e ) 0.5 ∼ 1 develops in the current sheet center (Norgren et al 2012;Yoo et al 2020;Wang et al 2022).…”