Characteristics Of MHD Waves Around The Heliospheric Current Sheet

Due to the activities of the solar corona,some wave structues are expected to evolve in interplanetary solar wind,heliospheric current sheet(HCS)the associated heliospheric plasma sheet(HPS).However,the magnetohydrodynamics(MHD)wave modes in the HCS and HPS have not been comprehensively investigated in the literature.Based on a frequency-related identification approach,the properties of MHD waves are investigated during 154 HCS crossings observed by the Wind spacecraft from 1995 to 2013.Through case analysis,we found that under different HPS values,the MHD fluctuations of the events are different.Further statistical analysis shows that the incidence of MHD waves around HCS/HPS is found to be modulated by the plasma within the HPS:(1) > 5,both Alfvén and slow waves obviously decay within the HPS,with the occurrence rate(OR)decreasing from 60% and 20% in the upstream/downstream to41% and 14% in the HPS vicinity,respectively;(2)1 < < 5,the OR of Alfvén waves(AWs)remains nearly stable.However,more slow waves are generated after the HCS crossing,with OR increasing from 13% in the upstream/downstream to 22%;(3) < 1,the OR of Alfvén and slow waves remains at 58% and 20% during the entire crossing,in spite of some irregular fluctuations.The results for the HCS without a clear HPS are similar to the situations of a low HPS.The parametric decay instability of AWs is proposed as being responsible for the more slow waves generated in the moderate HPS,and some indirect observational clues are also given.Based on the results of previous studies on the classification of solar wind,this paper also used a frequency-related method to detect fluctuations to make a statistical analysis of the fluctuations in the plasma of different sources of solar wind.It is found that the incidence of anti-sunward propagating Alfvén waves in the plasma originated from coronal holes is the highest,about 72 %,and Streamer-belt-origin plasma is the second.Sector reversal region plasma and ejecta plasma is the least,about 40 %.The incidence of slow waves and sunward propagating Alfvén waves is just the opposite,and the specific mechanism that causes this difference remains to be studied.In summary,our study is the first time to statistically analyze the characteristics of MHD waves near HCS/HPS and found that the characteristics of MHD fluctuations are closely related to the plasma value.The observation evidence of the Alfvén waves parametric decay instability on the generation of slow waves in HPS is also given,which provides a new observation clue for us to better understand the wave mode conversion of MHD waves near HCS.