Studies Of The Rotation,Nonradial Motion And Associated Geo-effectiveness Of CME Magnetic Flux Rope

Coronal mass ejections(CMEs)are large-scale eruptions of plasma and magnetic field from the Sun and are major drivers of space weather effects.When propagating in the heliosphere,they are called interplanetary CMEs(ICMEs).It is of great importance to study the characteristics of CME/ICME for spaceweather forecast.One of the intriguing question concerning their eruption,propagation and geo-effectiveness is how to forecast their southward component of CME magnetic fields.Recent studies find that many CMEs have a magnetic flux rope(MFR)structure.It is very important to study the propagation and change of MFR from the solar face to interplanetary space for space weather predic-tion.In this dissertation,using remote sensing observations and in situ measurements from multiple-spacecrafts at multiple positions,the authors study the rotation,nonradial motion and associated geo-effectiveness of CME magnetic flux rope.The authors analyze the 2015 December 16 CME,based on the remote sensing and in situ observations from SDO,SOHO,STEREO A and Wind,using the Graduated Cylin-drical Shell(GCS)model,the Grad-Shafranov(G-S)technique and the Nonlinear Force-Free Field(NLFFF)method.Conclusions are as follows:(1)the CME changed its propa-gation direction by about 45° in latitude and about 30° in longitude in the low corona due to the asymmetric distribution of the magnetic energy around the source region.The authors obtain the coronal magnetic field of the AR from the NLFFF method.The magnetic en-ergy density distribution on different layers show a gradient descent toward the northeast of the AR,which is consistent with the CME propagation direction.This indicates that the coronal magnetic field context of the AR plays an important role in the CME propagation direction.(2)the MFR rotated counterclockwise by about 95O in the low corona during the eruption,which,again,can be attributed to the coronal magnetic field configuration around the AR.The MFR was nearly horizontal in the solar source region,but became largely southward in the extended corona and near the Earth.Previous studies of the role of the magnetic tension force in the MFR rotation suggest that the rotation direction of an MFR is determined by the sign of helicity of the source region(MFR):the positive(right-handed)ones rotate clockwise,while the negative(left-handed)ones rotate coun-terclockwise.In our case,the MFR is right-handed but rotates counterclock:wise.The geometry of the MFR in relation to the AR coronal magnetic field context is considered to be an important factor for the rotation.(3)The MFR in the source region is almost hor-izontal,while the orientation of the MFR points to the south when it arrives at the Earth.The axial magnetic component is the main contributor to the southward magnetic field in the magnetic cloud,producing the relatively intense geomagnetic storm.It reveals that the rotation plays a great role in the CME geo-effectiveness.The new findings in this dissertation are as follows:(1)based on different measurements from multi-spacecraft,we obtain the accurate structure of CME MFR from solar source region to 1 AU.The results show that the rotation and nonradial motion of CME MFR mainly occurred in the low corona.The low coronal magnetic field plays an important role in the rotation and nonradial motion of CME MFR.(2)the authors obtain the magnetic field of the source region with NLFFF extrapo-lation method and analyze the magnetic energy density distribution of the source region.We find that the asymmetric magnetic field around the MFR caused the the rotation and nonradial motion of CME MFR.(3)the authors analyze the structure of MFR in the magnetic cloud near the Earth and find that the rotation of MFR can change the intensity and time duration of the southward component of CME magneitc fields.It will affect the geo-effectiveness of the CME.