Numerical studies of the Kelvin-Hemholtz instability in a coronal jet  

作　　者：Tian-Le Zhao Lei Ni Jun Lin Udo Ziegler 

机构地区：[1]Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, China [2]University of Chinese Academy of Sciences, Beijing 100049, China [3]Center for Astronomical Mega-Science, Chinese Academy of Sciences, Beijing 100101, China [4]Leibniz-Institut fur Astrophysik Potsdam, Potsdam D-14482, Germany

出　　处：《Research in Astronomy and Astrophysics》2018年第4期91-104,共14页天文和天体物理学研究（英文版）

基　　金：supported by the National Natural Science Foundation of China (Grant Nos. 11573064, 11203069, 11333007, 11303101 and 11403100);the National Basic Research Program of China (973 program, 2013CBA01503);the NSFCCAS Joint Fund (U1631130); the CAS grant QYZDJSSW-SLH012;the Western Light of Chinese Academy of Sciences 2014;the Youth Innovation Promotion Association, CAS 2017;the Key Laboratory of Solar Activity (Grant KLSA201404);the NSFC-Guangdong Joint Fund (U1501501, nsfc2015460 and nsfc2015-463)

摘　　要：Kelvin-Hemholtz（K-H）instability in a coronal EUV jet is studied via 2.5D MHD numerical simulations.The jet results from magnetic reconnection due to the interaction of the newly emerging magnetic field and the pre-existing magnetic field in the corona.Our results show that the Alfv e′n Mach number along the jet is about 5–14 just before the instability occurs,and it is even higher than 14 at some local areas.During the K-H instability process,several vortex-like plasma blobs with high temperature and high density appear along the jet,and magnetic fields have also been rolled up and the magnetic configuration including anti-parallel magnetic fields forms,which leads to magnetic reconnection at many X-points and current sheet fragments inside the vortex-like blob.After magnetic islands appear inside the main current sheet,the total kinetic energy of the reconnection outflows decreases,and cannot support the formation of the vortex-like blob along the jet any longer,then the K-H instability eventually disappears.We also present the results about how the guide field and flux emerging speed affect the K-H instability.We find that a strong guide field inhibits shock formation in the reconnecting upward outflow regions but helps secondary magnetic islands appear earlier in the main current sheet,and then apparently suppresses the K-H instability.As the speed of the emerging magnetic field decreases,the K-H instability appears later,the highest temperature inside the vortex blob gets lower and the vortex structure gets smaller.Kelvin-Hemholtz（K-H）instability in a coronal EUV jet is studied via 2.5D MHD numerical simulations.The jet results from magnetic reconnection due to the interaction of the newly emerging magnetic field and the pre-existing magnetic field in the corona.Our results show that the Alfv e′n Mach number along the jet is about 5–14 just before the instability occurs,and it is even higher than 14 at some local areas.During the K-H instability process,several vortex-like plasma blobs with high temperature and high density appear along the jet,and magnetic fields have also been rolled up and the magnetic configuration including anti-parallel magnetic fields forms,which leads to magnetic reconnection at many X-points and current sheet fragments inside the vortex-like blob.After magnetic islands appear inside the main current sheet,the total kinetic energy of the reconnection outflows decreases,and cannot support the formation of the vortex-like blob along the jet any longer,then the K-H instability eventually disappears.We also present the results about how the guide field and flux emerging speed affect the K-H instability.We find that a strong guide field inhibits shock formation in the reconnecting upward outflow regions but helps secondary magnetic islands appear earlier in the main current sheet,and then apparently suppresses the K-H instability.As the speed of the emerging magnetic field decreases,the K-H instability appears later,the highest temperature inside the vortex blob gets lower and the vortex structure gets smaller.

关 键 词：Sun corona jet — Kelvin-Hemholtz instability — guide-field — method numerical simulations 

分 类 号：P353[天文地球—空间物理学]