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The role of aerodynamic drag in dynamics of coronal mass ejections

Published online by Cambridge University Press:  01 September 2008

Bojan Vršnak ,
Dijana Vrbanec ,
Jaša Čalogović  and
Tomislav Žic
Bojan Vršnak
Affiliation:
Hvar Observatory, Faculty of Geodesy, Kačićeva 26, HR-10000 Zagreb, Croatia email: bvrsnak@geof.hr
Dijana Vrbanec
Affiliation:
Hvar Observatory, Faculty of Geodesy, Kačićeva 26, HR-10000 Zagreb, Croatia email: bvrsnak@geof.hr
Jaša Čalogović
Affiliation:
Hvar Observatory, Faculty of Geodesy, Kačićeva 26, HR-10000 Zagreb, Croatia email: bvrsnak@geof.hr
Tomislav Žic
Affiliation:
Hvar Observatory, Faculty of Geodesy, Kačićeva 26, HR-10000 Zagreb, Croatia email: bvrsnak@geof.hr
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Abstract

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Dynamics of coronal mass ejections (CMEs) is strongly affected by the interaction of the erupting structure with the ambient magnetoplasma: eruptions that are faster than solar wind transfer the momentum and energy to the wind and generally decelerate, whereas slower ones gain the momentum and accelerate. Such a behavior can be expressed in terms of “aerodynamic” drag. We employ a large sample of CMEs to analyze the relationship between kinematics of CMEs and drag-related parameters, such as ambient solar wind speed and the CME mass. Employing coronagraphic observations it is demonstrated that massive CMEs are less affected by the aerodynamic drag than light ones. On the other hand, in situ measurements are used to inspect the role of the solar wind speed and it is shown that the Sun-Earth transit time is more closely related to the wind speed than to take-off speed of CMEs. These findings are interpreted by analyzing solutions of a simple equation of motion based on the standard form for the drag acceleration. The results show that most of the acceleration/deceleration of CMEs on their way through the interplanetary space takes place close to the Sun, where the ambient plasma density is still high. Implications for the space weather forecasting of CME arrival-times are discussed.

Keywords

Sun: coronal mass ejections (CMEs)Sun: corona(Sun:) solar wind(Sun:) solar-terrestrial relations(magnetohydrodynamics:) MHD
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Symposium S257: Universal Heliophysical Processes , September 2008 , pp. 271 - 277
Copyright
Copyright © International Astronomical Union 2009

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