Low-latitude Sunspot Group Tilt Angles in 15–24 Activity Cycles

Abstract An analysis of the tilt angles of the active regions in 15–24 activity cycles was performed. We used data from measurements of magnetic fields in the sunspot umbra in the period 1918–2019 at the Mount Wilson Observatory, as well as the tilt angles of active regions in “white” light at the Kodaikanal and Mount Wilson observatories in activity cycles 15–21. The mean tilt angles of active regions <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:math> and the slope μ from latitude θ in the activity cycles are considered. Low-latitude bipoles are the most important in predicting the strength of solar cycles. In this work, we selected the cutoff latitude θ cut at which the highest correlation is observed with the strength of the next activity cycle for active regions with latitude θ &lt; θ cut . It was found that for magnetic field measurement data, the highest correlation of the parameters <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:math> and μ with the strength of the next solar activity cycle is characteristic of bipoles in the equatorial zone with θ &lt; θ cut ≈ 14 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 2. For “white” light observation data, θ cut ≈ 8 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 5 for Mount Wilson Observatory and θ cut ≈ 9 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 4 for Kodaikanal Observatory.