Tilt of Sunspot Bipoles in Solar Cycles 15 to 24 |
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| Authors: | " target="_blank">Ksenia Tlatova " target="_blank">Andrey Tlatov Alexei Pevtsov " target="_blank">Kalevi Mursula Valeria Vasil’eva Elina Heikkinen Luca Bertello Alexander Pevtsov " target="_blank">Ilpo Virtanen Nina Karachik |
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| Institution: | 1.St. Petersburg State University,Saint Petersburg,Russia;2.Kislovodsk Mountain Astronomical Station of Pulkovo Observatory,Kislovodsk,Russia;3.Kalmyk State University,Elista,Russia;4.National Solar Observatory,Boulder,USA;5.ReSoLVE Centre of Excellence, Space Climate Research Unit,University of Oulu,Oulu,Finland;6.Astronomical Institute AS RUz,Tashkent,Uzbekistan |
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| 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 as regards polarity and strength of magnetic field in sunspots. We identified 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 (\(\gamma\)) on latitude (\(\varphi\)) was found to be \(\gamma= (0.20\pm0.08) \sin(2.80 \varphi) + (-0.00\pm0.06)\). 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. |
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