Tilt of Sunspot Bipoles in Solar Cycles 15 to 24

Abstract

We use recently digitized sunspot drawings from Mount Wilson Observatory to investigate the latitudinal dependence of tilt angles of active regions and its change with solar cycle. The drawings cover the period from 1917 to present and contain information about polarity and strength of magnetic field in sunspots. We identify clusters of sunspots of same polarity, and used these clusters to form "bipole pairs". The orientation of these bipole pairs was used to measure their tilts. We find that the latitudinal profile of tilts does not monotonically increase with latitude as most previous studies assumed, but instead, it shows a clear maximum at about 25-30 degree latitudes. Functional dependence of tilt (γ) on latitude (ϕ) was found to be γ = (0.20 ± 0.08) sin(2.80ϕ) + (−0.00 ± 0.06). We also find that latitudinal dependence of tilts varies from one solar cycle to another, but larger tilts do not seem to result in stronger solar cycles. Finally, we find the presence of a systematic offset in tilt of active regions (non-zero tilts at the equator), with odd cycles exhibiting negative offset and even cycles showing the positive offset.

Long-term studies of photospheric magnetic fields on the Sun

“…Livingston et al, 2006;Penn and Livingston, 2006;Pevtsov et al, 2011Pevtsov et al, , 2014bRezaei et al, 2012;Watson et al, 2011) and sunspot-area -maximum field strength relation (Nagovitsyn et al, 2017). The data have also been implemented to the study the tilt of active regions (Joy's law Tlatova et al, 2018), reconstruction of polar fields (Pevtsov et al, 2016) and magnetic momentum of active regions (Virtanen et al, 2019b).…”

Solar cycle prediction

“…The occurrence rate of anti-Hale regions was found to be 8.5%. Tilts of active regions taking into account the magnetic polarities of spots were recently also determined byTlatova et al (2018) from the archive of solar drawings at Mt.Wilson Observatory: these drawings include polarity information since 1917. Their results concerning cycle dependence of tilts are inconclusive.…”

Bipoles That Violate the Laws of Joy and Hale in the 15–24th Activity Cycles

“…Эта закономерность, найденная Джоем [1], вместе с законом Хейла [2] о смене полярности ведущих и хвостовых пятен в 22-летнем цикле является, возможно, одними из основных причин существования солнечного магнитного цикла [3,4]. Позже закон Джоя был подтвержден во многих работах [5,6]. В настоящее время считается, что закон Джоя вызван действием силы Кориолиса, которая разворачивает всплывающие магнитные поля, образующие солнечные пятна [7].…”

“…В работе [8] на основе анализа магнитограмм MDI/SOHO и HMI/SDO было найдено, что около 8% маг-нитных активных образований нарушают правило Хейла полярности ведущих и хвостовых групп. В работах [4,5]…”