Coronal mass ejections and space weather

David F. Webb*
Institute for Scientific Research, Boston College, 140 Commonwealth Ave., Chestnut Hill, MA 02457, U.S.A.

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Severe space weather effects can cause spacecraft damage and orbit degradation, increases of radiation dosage to people on aircraft and to astronauts, and damage to power lines and power stations. Such effects are usually associated with geomagnetic storms, the largest of which are driven by coronal mass ejections (CMEs). CMEs are typically observed in white light near the Sun by coronagraphs, recently the SOHO LASCO and the STEREO SECCHI CORs. In the last decade two heliospheric imagers have added wide-field viewing capabilities of CMEs in the heliosphere, the Solar Mass Ejection Imager (SMEI) in Earth orbit and the STEREO Heliospheric Imagers (HIs) in 1 AU solar orbits. Many CMEs have now been observed by these instruments and their signatures detected in–situ at Earth=L1 and/or by one or both STEREO spacecrafts. Other highlights include the following. During the last extended minimum, solar activity was very low and geostorm activity was the lowest in the last 80 years. The linear relationship between CME and sunspot rates has been maintained for 4 solar cycles, although there is evidence that the rates are diverging during the current cycle, possibly related to weak polar fields. Recent near-real time arrival-time predictions for several CMEs demonstrate that combinations of LASCO, STEREO and SMEI data can significantly improve forecasts. In the last decade heliospheric imager data have been used for 3-D CME reconstructions to study their propagation and kinematics and to improve our knowledge of space weather, but no new Earth-based instruments are planned.

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Keywords : coronal mass ejections – space weather – magnetic clouds