A Statistical Study of the Average Iron Charge Distributions inside   Magnetic Clouds for Solar Cycle 23
  Magnetic clouds (MCs) are the interplanetary counterpart of coronal magnetic flux ropes. They can provide valuable information to reveal the flux rope characteristics at their eruption stage in the corona, which are unable to be explored in situ at present. In this paper, we make a comprehensive survey of the average iron charge state (<Q>Fe) distributions inside 96 MCs for solar cycle 23 using ACE (Advanced Composition Explorer) data. As the <Q>Fe in the solar wind are typically around 9+ to 11+, the Fe charge state is defined as high when the <Q>Fe is larger than 12+, which implies the existence of a considerable amount of Fe ions with high charge states (e.g., \geq 16+). The statistical results show that the <Q>Fe distributions of 92 (~ 96%) MCs can be classified into four groups with different characteristics. In group A (11 MCs), the <Q>Fe shows a bimodal distribution with both peaks higher than 12+. Group B (4 MCs) presents a unimodal distribution of <Q>Fe with its peak higher than 12+. In groups C (29 MCs) and D (48 MCs), the <Q>Fe remains higher and lower than 12+ throughout ACE passage through the MC, respectively. Possible explanations to these distributions are discussed. 
Hongqiang Song, Ze Zhong, Yao Chen, Jie Zhang, Xin Cheng, Liang Zhao,   Qiang Hu, Gang Li
astro-ph.SR physics.space-ph