Observation And Statistical Study Of The Properties Of The Kelvin-Helmholtz Waves On The Magnetopause Under Northward Interplanetary Magnetic Field

This paper mainly focuses on 1. the observation of Kelvin-Helmholtz(K-H)waves on the magnetopause under the northward interplanetary magnetic ?eld(IMF) by the Time History of Events and Macroscale Interactions during Substorms(THEMIS), and 2. the statistical study of the K-H wave properties and their relationship with the interplanetary conditions by combining more observation results of other spacecrafts. The entire plasma and magnetic ?eld data of the probes B and C, namely the outer most two probes of THEMIS, during the year of 2008 and 2009 are searched. 14 K-H wave events with rolled-up vortices are identi?ed using the criteria for K-H instability detection in single-spacecraft observation. The systematic method to calculate the wave parameters of K-H waves, including the dominant period, phase velocity, and wavelength, is proposed. The period is determined by three kinds of spectrograms: the Fourier Spectrum, wavelet analysis, and Lomb-Scargle periodogram for three key parameters: the ion density, ion temperature, and Z component of the magnetic?eld. The vortex center-of-mass velocity approximation is proposed to estimate the phase velocity of K-H waves, namely approximating the propagation velocity with the center-of-mass velocity of the detected K-H vortex. The K-H wavelength is thus obtained. Another 42 K-H wave events observed by Geotail, TC-1, and Cluster are collected after a survey of previous research. These events together with the 14 new events identi?ed by ourselves from the observation of THEMIS,consist of a data set for a statistical study. Having determined the wave parameters and interplanetary conditions of each event, we investigate preliminarily the statistical properties of K-H waves and their dependence on the interplanetary conditions. The K-H period is found to tend to be shorter with a lower solar wind speed, and longer with a larger IMF clock angle. And The K-H wavelength gradually increases along the low latitude boundary layer toward the nightside.The analysis method of this paper is helpful in deepening our understanding of the K-H wave on the magnetopause, and the statistical results provide newobservational support for the solar wind-magnetosphere interactions.