Studies Of The Interaction Between Slow Coronal Mass Ejections And High Speed Solar Wind

The modern human technological society is severely influenced by the space weather.Coronal Mass Ejections(CMEs;ICMEs are the heliospheric counterpart of CMEs)are major eruption phenomenon in the solar system and one of the important contributors to space weather.It is important to analyze the CME propagation in the inner heliosphere and establish the connection between CMEs in the solar source region and geo-effectiveness produced by ICMEs,which can advance our knowledge of the critical role of CMEs in space weather prediction.We investigate the interplanetary propagation and evolution properties of slow CMEs by using remote sensing observations and solar wind in situ measurements from diverse spacecraft at different positions in this dissertation,including the speed,propagation direction,structure of the CME flux rope,the morphological evolution,and interaction with the background solar wind.These characteristics will help us to improve our understanding on how CME evolution in the inner heliosphere enhances space weather.In this dissertation,the author presents a comprehensive analysis of a geo-effective stealth CME that occurred on 2016 October 8,combining remote sensing and in situ observations from SDO,STEREO,SOHO and Wind.By using a graduated cylindrical shell method,the authors estimate the propagation direction and the structure of the CME near the Sun.CME kinematics are determined from the wide-angle imaging observations of STEREO A.We also compare ENLIL MHD simulation results with in situ measurements to illustrate the context where the CME was propagating.The Grad-Shafranov technique is applied to reconstruct the flux rope structure from in situ measurements in order to understand the geo-effectiveness associated with the CME structure.Key conclusions are obtained as follows:(1)the CME was a stealth CME without clear low coronal signatures.It shows a clear acceleration followed by a nearly constant speed around the average solar wind level within 1 AU.The result is consistent with a speed profile of a typical slow CME.(2)EUV observations and the PFSS extrapolation of the coronal magnetic field suggest that there were low-latitude coronal holes,which could produce high-speed streams to interact with the CME in interplanetary space and influence the CME propagation and evolution.(3)the CME was bracketed between a slow wind ahead and a high speed stream behind,which enhanced the southward magnetic field inside the CME and gave rise to the unexpected geomagnetic storm.These results,again,suggest that slow CMEs have a high potential to interact with other solar wind structures in interplanetary space due to their slow motion.And the results also indicate the crucial importance of CME interplanetary evolution for accurate space weather prediction.This seems particularly important for solar cycle 24,although weak,because slow CMEs and low-latitude coronal holes are ubiquitous features of the solar cycle.A weak solar cycle does not necessarily implies weak geomagnetic activity.In this dissertation,there are three characteristics and main innovations:(1)The author gives an comprehensive analyzes on the propagation morphology and kinematics of a stealth CME from the corona to interplanetary space(?1 au).This slow CME travels in a gradual acceleration then in a constant speed,which is consistent with previous studies of typical slow CMEs;(2)Combination of observation and MHD simulation reveals the context where the stealth CME was propagating in interplanetary space and CME's evolution from different angle.This study also provides the influence of large-scale solar wind structures to the evolution of CMEs,which is critical to understand CMEs' geo-effectiveness;(3)The author processes variety of data from multiple spacecraft with the help of several methods.The author shows the significance of high speed streams from lowlatitude coronal holes to the propagation of slow CMEs and their related geo-effectiveness in the weak solar cycle.