1. Institute of Space Sciences, Shandong University, Weihai, Shandong 264209, People's Republic of China
2. Center for Integrated Research on Space Science, Astronomy, and Physics, Institute of Frontier and Interdisciplinary Science, Shandong University, Qingdao, Shandong 266237, People's Republic of China
3. Department of Physics, Auburn University, Auburn, Alabama 36849, USA