Meridional Motions and Reynolds Stress Determined by Using Kanzelh\"{o}he Drawings and White Light Solar Images from 1964 to 2016

TL;DR

This study analyzes sunspot data from 1964 to 2016 to investigate solar meridional motions and Reynolds stress, confirming their role in maintaining the Sun's differential rotation.

Contribution

It provides a long-term analysis of solar velocity patterns using Kanzelhöhe data, confirming Reynolds stress as the main mechanism for angular momentum transport.

Findings

Reynolds stress transports angular momentum towards the equator.

The differential rotation profile aligns with previous studies.

KSO data quality is sufficient for solar velocity analysis.

Abstract

Sunspot position data obtained from Kanzelh\"{o}he Observatory for Solar and Environmental Research (KSO) sunspot drawings and white light images in the period 1964 to 2016 were used to calculate the rotational and meridional velocities of the solar plasma. Velocities were calculated from daily shifts of sunspot groups and an iterative process of calculation of the differential rotation profiles was used to discard outliers. We found a differential rotation profile and meridional motions in agreement with previous studies using sunspots as tracers and conclude that the quality of the KSO data is appropriate for analysis of solar velocity patterns. By analysing the correlation and covariance of meridional velocities and rotation rate residuals we found that the angular momentum is transported towards the solar equator. The magnitude and latitudinal dependence of the horizontal component of the Reynolds stress tensor calculated is sufficient to maintain the observed solar differential rotation profile. Therefore, our results confirm that the Reynolds stress is the dominant mechanism responsible for transport of angular momentum towards the solar equator.