Dayside Magnetopause Location During Radial Interplanetary Magnetic Field Periods

Wednesday, 17 December 2014
Hui Wang1,2, Tao Huang2, Jih-Hong Shue3 and Aaron J Ridley1, (1)Univ Michigan, Ann Arbor, MI, United States, (2)School of Electronic Information, Wuhan University, Dept. of Space Physics, Wuhan, China, (3)NCU National Central University of Taiwan, Jhongli, Taiwan
The present work has investigated the dayside magnetopause locations under radial interplanetary field (IMF) conditions. During 49 earthward radial IMF events from years of 2001 to 2009, Cluster satellites have crossed the dayside magnetopause for 11 times. Among them, there are 8 events occurring at mid latitudes. The observed locations of the magnetopause are compared with the widely used magnetopause model (Shue et al., 1998). The model performance exhibits local time asymmetry at mid latitudes. The observed magnetopause contracts in the prenoon while expands in the postnoon. This local time asymmetry is confirmed by GOES magnetic field observations at geosynchronous orbits. The result might confirm the bullet shape magnetopause during radial IMF period. The model-observation differences during radial IMF periods correlate well with the solar wind dynamic pressure at mid-latitudes. The present work has indicated the important role of the IMF cone angle and dipole tilt angle in the modulation of the magnetopause shape at midlatitudes. Larger IMF cone angle or smaller dipole tilt angle can make the southern magnetopause expand further outward.