Studies Of The Propagation Properties Of Coronal Mass Ejections In The Inner Heliosphere

Space weather can significantly impact the modern human economic society. Coro-nal Mass Ejections (CMEs; also called ICMEs when they are propagating in interplane-tary space) are one of the important contributors to space weather. In this dissertation,based on remote sensing observations and solar wind in situ measurements from multiple spacecraft at multiple positions, the authors investigate the inner-heliospheric propagation properties of CMEs including the speed, associated Type II radio burst, structure of the CME flux rope, propagation direction and the morphological evolution. Investigation of these characteristics is helpful in understanding the space-weather effectiveness of CMEs.The authors analyze the 2012 July 12 fast CME that triggered a geomagnetic storm,basing on the remote sensing and in situ observations from spacecraft STEREO, SDO, VEX and Wind, using a triangulation method, the Grad-Shafranov technique, etc. Conclusions are as follows: (1) the CME underwent an impulsive acceleration, a rapid deceleration and then a gradual deceleration before arriving at 1 au. The rapid deceleration ceased before the CME reached the orbit of Mercury (?0.4 au). This is different from a previ-ous statement that a fast CME could constantly decelerate until reaching 0.76 au, which should be considered in CME kinematics models; (2) the associated type II radio burst was probably produced from a high-density interaction region between the CME-driven shock and a nearby streamer or from the shock flank with lower heights, which implies uncertainties in the determination of the CME kinematics using solely the type II radio burst; and (3) the orientation of the CME flux-rope structure near the Earth was largely southward, which agrees with the tilt angle of the neutral line in the solar source region.The magnitude of the axial magnetic field of the CME flux rope was roughly twice that of the azimuthal component. Thus, the southward magnetic field triggering the geomag-netic storm was mainly from the axial component. This indicates that predicting both the flux-rope orientation and magnitudes of magnetic field components is key to forecasting CME triggered geomagnetic activity.A CME with a relatively low speed launched on 2010 September 4 has also been studied in this work. The CME flux rope was probably linking two active regions (ARs)11101 and 11103 that were on the west side of the source region. Using a Potential-Field Source-Surface (PFSS) magnetic field extrapolation model, the Graduated Cylindrical Shell (GCS) model fitting and a triangulation method, the authors investigate the remote sensing and in situ observations from SDO, STEREO, SOHO, VEX and Wind, and obtain the following key results: (1) the CME was deflected eastward in the low corona by the magnetic pressure from the two ARs on the west side of the source region. The CME possibly interacted with another ejection, which caused that the CME continued turning eastward in interplanetary space and arrived at VEX (Venus) that was ?90° east of the source region. This illustrates the necessity of considering both the background magnetic field configuration and other successive eruptions near the source region in determining the propagation direction of a CME; (2) the triangulation estimated arrival times at VEX and Wind are generally consistent with those in situ measured by the spacecraft, which sug-gests that the simple assumed circle attached to the Sun may partially describe the shape of the eastern CME front in the inner heliosphere. Although VEX was closer to the Sun,the observed and estimated CME arrival times at VEX are not earlier than those at Wind.These indicate the importance of determining both the frontal shape and the propagation direction for estimating the arrival time of a CME; and (3) the ICME was compressed in the radial direction and was extended in the longitudinal direction, leading to a large transverse size of the flux-rope cross section in the ecliptic plane.The novelties and features in this dissertation are as follows:(1) using the stereoscopic wide-angle imaging observations from two spacecraft, the authors determine the speed evolution and the direction deflection of the propagation of the CME from the corona to interplanetary space( 1 au) and confirm that the deceleration of fast CMEs is faster than suggested in previous studies;(2) the comparison between the multi-spacecraft stereoscopic imaging observations and multi-point solar wind in situ measurements places constants on the kinematics and the morphology of the CME in the inner heliosphere;(3) by employing several methods to analyze various kinds of data from multiple spacecraft, the authors reveal the effect of the environmental magnetic field configuration of the CME source region on the CME propagation direction and provide a new method to obtain key clues to the source region of the type ? radio burst.