1. School of Astronomy and Space Science, Nanjing University, Nanjing 210023, China
2. Key Laboratory for Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210023, China
3. Department of Mathematics, Southeast University, Nanjing 210096, China
4. CAS Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China