Relationship between the Tilt Angles of Sunspot Groups and the Properties of the Next Solar Cycle

Abstract

Based on the data from the Kodaikanal and Mount Wilson observatories, we investigate the relationships of the tilt angles of sunspot groups, including the mean tilt angle and the tilt-angle scatter, during the declining phase with the parameters of the next solar cycle (SC). The main findings are summarized in the following three points. (1) During the declining phase, the correlation between the mean tilt angle and the tilt-angle scatter is statistically insignificant. (2) Six quantities measured during the declining phase show significant anticorrelations with the strength and amplitude of the next SC and positive correlations with the duration of the ascending phase of the next SC: the standard deviation of the tilt angles, the rms tilt angle, the mean absolute value of the tilt angles, the area-weighted absolute value of the tilt angles, the latitude-weighted absolute value of the tilt angles, and the area- and latitude-weighted absolute value of the tilt angles. (3) The correlations of the mean tilt angle, the area-weighted tilt angle, the latitude-weighted tilt angle, and the area- and latitude-weighted tilt angle during the declining phase with the strength, amplitude, and duration of the ascending phase of the next SC are statistically insignificant. These findings demonstrate that the modulation of the parameters of the next SC by the tilt-angle scatter during the declining phase plays a vital role in regulating SC variability.

Keywords

• Solar cycle
• sunspot groups
• Solar dynamo