We report on the determination of radial magnetic field strength in the heliocentric distance range from 6 to 120 solar radii (R☉) using data from Coronagraph 2 (COR2) and Heliospheric Imager I (HI1) instruments onboard the Solar Terrestrial Relations Observatory (STEREO) spacecraft following the standoff-distance method of Gopalswamy and Yashiro (2011). We measured the shock standoff distance of the 2008 April 5 Coronal Mass Ejection (CME) and determined the flux rope curvature by fitting the 3D shape of the CME using the Graduated Cylindrical Shell (CGS) model. The radial magnetic field strength is computed from the Alfvén speed and the density of the ambient medium. We also compare the derived magnetic field strength with in-situ measurements made by the Helios spacecraft, which measured the magnetic field at the heliocentric distance range from 60 to 215 R☉. We found that the radial magnetic field strength decreases from 28 mG at 6 R☉ to 0.17 mG at 120 R☉. In addition, we found that the radial profile can be described by a power law.
Authors: Watanachak Poomvises, Nat Gopalswamy, Seiji Yashiro, Ryun Young Kwon, Oscar Olmedo
Publication Status: Published
Last Modified: 2013-01-08 10:43