AN EXAMINATION OF THE SUNSPOT AREAL DATASET, 1875–2017: PAPER II, HEMISPHERIC DIFFERENCES

Abstract

This is the second paper in an anticipated three-part study of the sunspot areal dataset. Examined are the annual variations of the northern (N) and southern (S) hemispheric sunspot area (SSA), number of active region entries (NARE), and the mean area per entry (MAE) for the interval 1875–2017, spanning solar cycles (SCs) SC12–SC24. For the overall interval of 1875– 2019, SSA(N) has been larger than SSA(S) for 77 of the 145 years. Likewise, for SC12–SC24, SSA(N) has been greater than SSA(S) during the ascending phase of the solar cycle (i.e., 35 of 52 years), whether the SC is an even- or odd-numbered SC, while SSA(S) has been greater than SSA(N) during the descending phase of the solar cycle (51 of 93 years). Minimum SSA(N) and SSA(S) have occurred in the same year in only 7 of 13 SCs, including SC14, SC16 and SC19– SC23. Maximum SSA(N) and SSA(S) have occurred in the same year only once (in SC15). Maximum SSA(S) usually occurs after maximum SSA(N), true for 9 of 13 SCs. Maximum SSA(S) preceded maximum SSA(N) in SC16, SC18, and SC19. Multiple peaks in SSA(N) or SSA(S), typically 2–3 years apart, have often been seen (e.g., SC12–SC16 and SC18–SC22). SC12 had the smallest maximum SSA(N) (452.0 millionths of a solar hemisphere), while SC19 had the largest maximum SSA(N) (2,277.2 millionths of a solar hemisphere). SC14 had the smallest SSA(S) (600.3 millionths of a solar hemisphere), while SC18 had the largest SSA(S) (1,642.9 millionths of a solar hemisphere). The average time from minimum to maximum SSA(N) is 3.8 years (range 2–5 years), while it is 4.8 years for SSA(S) (range 3–6 years). The average time from maximum SSA(N) to the following minimum SSA(N) is 6.9 years (range 5–9 years), while it is 6.2 years for SSA(S) (range 5–8 years). The largest N-S asymmetry coefficients for SSA occurs between –3 and +1 years about sunspot minimum. The largest N-S asymmetry coefficient in SSA occurred in 2019 (SC24). The largest area sunspot occurred in 1947 (SC18) in the southern hemisphere and measured 6,132 millionths of a solar hemisphere, nearly twice the size of the average maxima of the largest area spots in the other 12 SCs. SSA and NARE are highly correlated with each other and with SSN. Minimum MAE(N) and MAE(S) may have occurred, respectively, in 2018 and 2019, highly suggestive that SSN(m) for SC25 either occurred in 2019 or will occur in 2020.