Evolution and DEM analysis of Early Structures of Coronal Mass Ejections by SDO-AIA

Cheng Xin, Nanjing University
Zhang Jie, George Mason University
Ding Ming-de, Nanjing University

Abstract
Recent Solar Dynamic Observatory observations reveal that some coronal mass ejections (CMEs) consist of multi-temperature structures: a hot channel and a cool leading edge (LE). The channel first appears as a twisted structure in the Atmospheric Imaging Assembly 94 A and 131 A passbands. The twisted hot channel initially lies along the polarity inversion line and then gradually develops into the less twisted semicircular structure during the impulsive phase of CME acceleration. In the meantime, the hot channel compresses the surrounding magnetic field and plasma, which successively stack into the CME leading front. Further kinematic analysis shows that, (1) the hot channel rises earlier than the first appearance of the CME leading edge and the onset of the associated flare; (2) the speed of the hot channel is always larger than that of the leading edge, at least in the field of view of AIA. It seems that the hot channel acts as a continuous driver of the CME formation and acceleration in the early acceleration phase, like the behaviors of flux rope in CME models and simulations. Moreover, through the differential emission measure analysis, it is confirmed that the channel is dominated by the plasma with high temperature (>8 MK) and high density (10^9cm^-3), while the leading edge and dimming region are mainly dominated by the low temperature plasma (~2-3MK).