Magnetohydrodynamics Waves In Solar Wind

In this paper,we carry out some researches on Magnetohydrodynamics waves in solar wind:1 Based on observation from WIND during 1995-2015,we make a comprehensive survey of Alfvénic fluctuations in ICMEs.The main findings are as follows:?1?Near1 au,the average occurrence rate of AFs in ICMEs is 26.2%,and 35.7%in solar wind.?2?AFs are prone to exist in high-speed ICMEs.?3?Both distributions of normalized T_p/T_expand AF occurrence rate across ICMEs show rising from front to rear,implying that AF dissipation contributes on local plasma heating inside ICMEs.2 Although it is believed that Alfvén waves can be present in the form of tor-sional modes in interplanetary magnetic flux ropes,convincing observational evidence remains elusive.In this Letter,we report the detection of Alfvén waves embedded within an interplanetary magnetic cloud on 2003 March 20,which exhibited quite dif-ferent features from those upstream and downstream.The magnetic field inside the magnetic cloud underwent alternate rotations along an arc through a relatively small angle in the plane perpendicular to the minimum variance direction,which seems con-sistent with the appearance of torsional modes.A significant poloidal motion of plasma existed in the MC,thus it is possible that the field-aligned helical plasma flow was mixed with Alfvén waves exhibiting high correlation between plasma velocity and magnetic field.3 First observational evidence of merging of two SIRs within 1 AU:Two neigh-boring SIRs may eventually coalesce to produce a merged interaction region en route to the outer heliosphere.However,instances of significant interaction and merging of two neighboring SIRs within 1 AU are thought to be extremely rare.In this paper,we present a case report of two interacting and merging SIRs observed near 1 AU,which was associated with two adjacent low-latitude coronal holes.The two SIRs were filled with outward propagating Alfvénic fluctuations associated with MHD turbulence.A reconnection exhaust associated with a current sheet was identified.We suggest that magnetic reconnection represented a potentially important mechanism for the merging of two neighboring SIRs.This observation may shed light on the understanding of the structure and formation of a merged interaction region within 1 AU.4 Previous studies,due to localized observation by single spacecraft,focused on sunward or anti-sunward Alfvén waves propagating along with magnetic field lines.In this Letter,for the first time,we use multi-spacecraft observation to verify and ana-lyze two large-scale magnetic clouds,when the spacecraft had quite different spatial separations.What surprised us is that not only unidirectional but bidirectional Alfvén waves exist in the large-scale magnetic cloud which is rooted to the Sun.We speculate that unidirectional Alfvén waves within a magnetic cloud are generated by distortions produced within a pre-existing flux rope,and bidirectional Alfvén waves are emitted from the center of reconnection and then travel outward along with two loop legs of a magnetic cloud.