Observations of Kelvin‐Helmholtz Waves in the Earth's Magnetotail Near the Lunar Orbit

Yiming Ling,A N Fazakerley,Anmin Tian,Binbin Tang,Hiroshi Hasegawa,Suiyan Fu,Xiao‐Chen Shen,Wenya Li,A W Degeling,Hui Zhang,Qiu‐Gang Zong,Motoharu Nowada,Quanqi Shi,Zuyin Pu,I J Rae

doi:10.1029/2018ja025183

Abstract

AbstractKelvin‐Helmholtz waves (KHWs), which have been widely observed at the magnetopause in the region near the Earth, play an essential role in the transport of solar wind plasma and energy into the magnetosphere under dominantly northward interplanetary magnetic field (IMF) conditions. In this study, we present simultaneous observations of KHWs under the northward IMF observed by both the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft in the Earth's magnetotail around the lunar orbit (at X ~ −50RE, Y ~ 30RE, dusk side) and the Geotail in the near‐Earth space (at X ~ −5RE, Y ~ −10RE, dawn side). The KHWs are quantitatively characterized by their dominant period, phase velocity, and wavelength, utilizing wavelet analysis and an approximation of their center‐of‐mass velocity. Our results suggest that the phase velocity and spatial scale of KHWs may increase as they propagate along the boundary layer toward the tail. Alternatively, the differences between the ARTEMIS and Geotail observations may indicate the possibility of dawn‐dusk asymmetry in the excited KHWs in this study. Our results strongly evidence the existence of the development of KHWs in terms of their wave frequency and scale size in the magnetotail and provide insight to the time evolution of KHWs along the magnetopause.

Highlights

The magnetopause, as the outer boundary of the terrestrial magnetosphere, is a critical region for entry of energy and particles from the solar wind into the magnetosphere
We present simultaneous observations of Kelvin-Helmholtz waves (KHWs) under the northward interplanetary magnetic field (IMF) observed by both the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon’s Interaction with the Sun (ARTEMIS) spacecraft in the Earth’s magnetotail around the lunar orbit and the Geotail in the near-Earth space
Our results suggest that the phase velocity and spatial scale of KHWs may increase as they propagate along the boundary layer toward the tail

Summary

Introduction

The magnetopause, as the outer boundary of the terrestrial magnetosphere, is a critical region for entry of energy and particles from the solar wind into the magnetosphere. With observations by the four Cluster spacecraft, Hasegawa et al (2004) found that KHWs can grow nonlinearly, and the resultant rolled-up vortices can mix the solar wind and magnetospheric plasmas. Takagi et al (2006) showed that the detection of low-density and faster-than-sheath magnetospheric plasma can be taken as a marker of rolled-up vortices This typical feature, together with quasi-periodic fluctuations (periods of 1–5 min) in the plasma parameters and magnetic fields under northward IMF, can be used as criteria to identify rolled-up vortices in single-spacecraft observations (Hasegawa et al, 2006; Taylor et al, 2012). The WIND spacecraft, which was 238RE away from the Earth (upstream), monitored IMF and solar wind conditions

Observations

Overview

Data Analysis

Findings

Discussion and Summary