Proc. International Living With A Star Workshop, p. 71−79, 2006
Solar Influence on the Heliosphere and Earth's Environment: Recent Progress and Prospects
N. Gopalswamy and A. Bhattacharyya (eds.)
19−24 February 2006, Goa, India.

Coronal Mass Ejections and Space Weather

D.F. Webb
Inst. for Scientific Research, Boston College, Chestnut Hill, MA, USA

N. Gopalswamy
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA


Coronal mass ejections (CMEs) are a key feature of coronal and interplanetary (IP) dynamics. Major CMEs inject large amounts of mass and magnetic fields into the heliosphere and, when aimed Earthward, can cause major geomagnetic storms and drive IP shocks, a key source of solar energetic particles. Studies over this solar cycle using the excellent data sets from the SOHO, TRACE, Yohkoh, Wind, ACE and other spacecraft and ground-based instruments have improved our knowledge of the origins and early development of CMEs at the Sun and how they affect space weather at Earth. A new heliospheric experiment, the Solar Mass Ejection Imager, has completed 3 years in orbit and has obtained results on the propagation of CMEs through the inner heliosphere and their geoeffectiveness. We review key coronal properties of CMEs, their source regions, their manifestations in the solar wind, and their geoeffectiveness. Halo-like CMEs are of special interest for space weather because they suggest the launch of a geoeffective disturbance toward Earth. However, not all halo CMEs are equally geoeffective and this relationship varies over the solar cycle. Although CMEs are involved with the largest storms at all phases of the cycle, recurrent features such as interaction regions and high speed wind streams can also be geoeffective.