A note on the torsional oscillation at solar minimum

TL;DR

This paper analyzes the evolution of solar zonal flow patterns during the current solar minimum, revealing slower movement of flow bands compared to previous cycles, which affects the apparent length of the solar cycle.

Contribution

It provides a comparative analysis of solar zonal flows during consecutive solar minima, highlighting differences in flow band movement and cycle timing.

Findings

Flow band movement towards the equator is slower than in previous cycles.

The current flow configuration resembles that at the previous cycle's onset.

The apparent length of the solar cycle has increased during 2007-2008.

Abstract

We examine the evolution of the zonal flow pattern in the upper solar convection zone during the current extended solar minimum, and compare it with that during the previous minimum. The results suggest that a configuration matching that at the previous minimum was reached during 2008, but that the flow band corresponding to the new cycle has been moving more slowly towards the equator than was observed in the previous cycle, resulting in a gradual increase in the apparent length of the cycle during the 2007 -- 2008 period. The current position of the lower-latitude fast-rotating belt corresponds to that seen around the onset of activity in the previous cycle.