Periodic Variations of Solar Corona Index during 1939–2020

Periodic behaviors of solar magnetic indicators might provide a clue for the understanding dynamic processes. Combining with Lomb–Scargle periodogram, concentration frequency and time via multitapered synchrosqueezed transform is applied to investigate periodic variations modified coronal index interval from 1 January 1939 31 August 2020. The main results are as follows: (1) During cycles 19 23, Schwabe cycle operating its length variating between 10.5 11-yr, average value 10.67-yr standard deviation 0.14-yr. (2) Rieger-type periods mainly distributed in range 120 200 days. In addition, vary somewhat intermittently during 18 24, which highest power 21 22 while much lower 23 24. (3) For rotation periods, temporal variation exhibits highly intermittent pattern an asymmetrical distribution 25th, 50th, 75th quantile 26, 27.8, 31-day, respectively. (4) Other mid-range also detected period 8.07, 5.44, 3.42, 2.3, 1.01-yr.