Hydrogen Lyman-Alpha Periodicity Behaviour During Various Solar Cycles.

Kotzé, Pieter

The temporal behaviour of various periodicities of hydrogen Lyman-alpha (Ly- α ) between 1950 and 2020 have been analysed using Lomb-Scargle and Morlet wavelets spectral analysis techniques. Daily mean values of Ly- α radiance (https://lasp.colorado.edu/lisird/data/composite%5flyman%5falpha/) for each individual year were used in this investigation to obtain the temporal behaviour of particularly the Rieger periodicity (150–180 days), the synodic solar rotation periodicity (≈ 27 days) as well as the elusive 13.5-day periodicity. Results obtained showed that the Rieger periodicity dominates at solar maximum during strong solar cycle conditions (Cycles 19, 21, 22, and 23), while the ≈ 27 -day periodicity is in most cases dominant during solar minima. On the other hand, the 13.5-day periodicity only appears above the 95% statistical confidence level during solar maxima of Cycles 19, 21, 22 and 24. Contrary to all previous Cycles since 1950, the 13.5-day periodicity appears exceptionally strong and above the 95% confidence level during the downward and minimum phases of Cycles 23 (2006) and 24 (2016) when its power exceeds that of the 27-day periodicity. This peculiar behaviour of the 13.5-day periodicity in Ly- α can probably be attributed to the anomalous asymmetrical structure of the solar magnetic field during Cycles 23 and 24.

SOLAR cycle; SOLAR magnetic fields; ROTATION of the Sun; MAGNETIC structure; WAVELETS (Mathematics); HYDROGEN

Astrophysics & Space Science, 2023, Vol 368, Issue 1, p1

0004-640X

Academic Journal

10.1007/s10509-023-04163-9