Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011spd....42.2311p&link_type=abstract
American Astronomical Society, SPD meeting #42, #23.11; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
STEREO/SECCHI observations help identify the true 3-D geometric structure of CMEs and track their true evolution in the inner heliosphere. Using STEREO observations, it is possible to obtain the true speed of CMEs, which is key in predicting the arrival time of CMEs at Earth (Gopalswamy et al. 2001). From the STEREO data, we are able to track and measure CMEs in 3-D by using Raytrace model (Thernisien et al 2006, 2009), which is free from projection effects and thus result in true CME velocities. Studied study 5 CME events, we found that the acceleration/deceleration of CMEs occur within 50 Rs from the Sun, after that the CME velocity converges to the narrow range (Poomvises et al 2010). Additionally, we found that expansion velocity of CMEs also converges to a narrow range after 50 Rs.
The observations are consistent with the theoretical flux rope model. The CME evolution can be explained by different forces that act on the CME: Lorentz force, thermal pressure force, gravity force, aero-dynamic drag force, and the magnetic drag force. The drag coefficient typically varies between 2.5 to 3.0, which is much smaller than the factor of twelve suggested by earlier studies. Moreover, the value of the polytropic index has been found to be between 1.35 to 1.60. Therefore, we have been able to narrow down the range of values for the drag coefficient and the polytropic index, which help in improve the prediction of CME travel time.
Gopalswamy Nat
Poomvises Watanachak
Zhang James J.
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