Generation of kinetic Alfven waves in the high-latitude near-Earth magnetotail: A global hybrid simulation

Abstract

In this paper, effects of a fast flow in the tail plasma sheet on the generation of kinetic Alfven waves (KAWs) in the high-latitude of the near-Earth magnetotail are investigated by performing a two-dimensional (2-D) global-scale hybrid simulation, where the plasma flow is initialized by the E  B drift near the equatorial plane due to the existence of the dawn-dusk convection electric field. It is found that firstly, the plasma sheet becomes thinned and the dipolarization of magnetic field appears around ðx; zÞ ¼ ðÀ10:5R E ; 0:3R E Þ, where R E is the radius of the Earth. Then, shear Alfven waves are excited in the plasma sheet, and the strong earthward flow is braked by the dipole-like magnetic field. These waves propagate along the magnetic field lines toward the polar regions later. Subsequently, KAWs with k ? ) k k are generated in the high-latitude magnetotail due to the existence of the non-uniformity of the magnetic field and density in the polar regions. The ratio of the electric field to the magnetic field in these waves is found to obey the relation ðdE z Þ=ðdB y Þ $ x=k k of KAWs. Our simulation provides a mechanism for the generation of the observed low-frequency shear Alfven waves in the plasma sheet and kinetic Alfven waves in the high-latitude near-Earth magnetotail, whose source is suggested to be the flow braking in the lowlatitude plasma sheet. V C 2015 AIP Publishing LLC. [http://dx.

Kinetic Alfvén Waves From Magnetotail to the Ionosphere in Global Hybrid Simulation Associated With Fast Flows

“…The tail KAWs continue to propagate away at = 2,527 s. By = 2,548 s, the flux tube has moved to (see the white field line in Figure a), and the wave energy has spread out over the field line. At later times, part of Shear Alfvén wave/KAW energy is seen to be reflected at the inner boundary, similar to that described in Guo et al (). Given that the average Alfvén speed along a tracked magnetic flux tube is around 1,500 km/s, it takes about 80–100 s for Shear Alfvén waves/KAWs to arrive at the inner boundary and be reflected.…”

“…Although KAWs have been observed in the magnetotail and ionosphere, their generation mechanisms and global transport properties are still unclear. Previous theories and simulations have shown that KAWs can be generated via various mechanisms such as magnetic reconnection (Liang et al, , ; Shay et al, ), mode conversion (Hasegawa & Chen, ; Johnson & Cheng, ), and phase mixing (Guo et al, ; Hasegawa, ; Vásconez et al, ). Shay et al () have shown the signature of KAWs generated by reconnection via a 2‐D particle‐in‐cell code.…”

Ion heating by Alfvén waves associated with dipolarization in the magnetotail: Two‐dimensional global hybrid simulation

“…flow by the dipole field, B x decreases and B z increases at (x, z) = (À10.5, 0.3) R E , and dipolarization appears. Such a process has been also found previously by Swift and Lin [2001] and Guo et al [2015].…”

“…The B y patterns along the field lines connecting to the thin plasma sheet corresponding to Alfvén waves in which the perturbations in V y are correlated with those in B y . As confirmed by our previous work [ Guo et al ., ], those Alfvén waves are excited by the interaction of the ion beams with the stationary near‐Earth plasma in the low‐latitude magnetotail, and they can propagate toward higher latitudes. The V y patterns illustrate the same phenomenon, which have an in‐phase (antiphase) correlation in the Southern (Northern) Hemisphere with wave vector k ∥ B (− B ) at t =27.0 and 36.0, is based on the Walén ratio [ Landau and Lifshitz , ].…”

Thermal electron anisotropy driven by kinetic Alfven waves in the Earth's magnetotail

“…KAWs as a natural mode of Alfven waves in hot ion plasma (Stasiewicz et al, 2000) are suggested to be generated by several different mechanisms, e.g., mode conversion (Hasegawa and Chen, 1975;Hasegawa, 1976;Lin et al, 2012;Johnson and Cheng, 1997), phase mixing (Guo et al, 2015) and magnetic reconnection (Chaston et al, 2005(Chaston et al, , 2009Liang et al, 2016;Wang et al, 2019b;Cheng et al, 2020). These waves are believed to be responsible for energy transfer from the magnetotail to 10 -1 10 0 10 1 10 2…”