Solar Interior Rotation and its Variation

Abstract

This article surveys the development of observational understanding of the interior rotation of the Sun and its temporal variation over approximately forty years, starting with the 1960s attempts to determine the solar core rotation from oblateness and proceeding through the development of helioseismology to the detailed modern picture of the internal rotation deduced from continuous helioseismic observations during solar cycle 23. After introducing some basic helioseismic concepts, it covers, in turn, the rotation of the core and radiative interior, the "tachocline" shear layer at the base of the convection zone, the differential rotation in the convection zone, the near-surface shear, the pattern of migrating zonal flows known as the torsional oscillation, and the possible temporal variations at the bottom of the convection zone. For each area, the article also briefly explores the relationship between observations and models.

Large-scale patterns and ‘active longitudes’

“…One can see that the acceleration occurs with a typical period of 1.4 years. In the declining phase of cycle 23, however, the acceleration is absent in agreement with the result by Howe (2009). …”

“…In the recent years, the oscillation periods of 1.3 years are not as clearly identified in helioseismic measurements as they were earlier (Howe, 2009). This raises the question of how reliable they are and how often they occur in the variation spectrum of different solar parameters.…”

Differential Rotation in Sun-like Stars from Surface Variability and Asteroseismology

“…At this point the acoustic oscillations used to measure rotation in the convection zone have lost much of their sensitivity to rotation, hence the large uncertainties in the rotation rate. However, the solid-body rotation profile is thought to continue down to the solar core (Howe 2009). …”

The Life Cycle of Active Region Magnetic Fields

“…Soon after the discovery of the torsional oscillation (a butterflylike equatorward propagating pattern of zonal flow residuals relative to the temporally averaged di↵erential rotation profile, see Howard & Labonte 1980, and chapter 9 of Howe, 2009), the Lorentz force has been invoked as a possible Fig. 9 Isosurface rendering of magnetic field strength in a convective dynamo simulation of a star rotating at ⌦ = 3⌦ by Nelson et al (2013).…”