Magnetic tracers, a probe of the solar convective layers

Abstract

A meridional circulation of sunspots has been measured through the digital analysis of the Meudon spectroheliograms from 1978 to 1983. Old and young sunspots follow a zonal meridional circulation, in several bands of latitude, in which two adjacent bands have opposite motions. This meridional circulation pattern is time-dependent. Using the H, filaments as magnetic field tracers, a large-scale magnetic pattern has been found that was also obtained independently by direct measurement of the magnetic field (Hoeksema, 1988).The coincidence of a large-scale magnetic pattern with a zonal meridional circulation suggests the existence of azimuthal rolls below the surface, and these azimuthal rolls can explain a number of properties of the solar cycle. New rolls occur with increasing proximity to the Equator, thereby indicating the direction of propagation of the dynamo wave. The occurrence of rolls is very favorable to the emergence of the magnetic regions. The rolls also influence the magnetic complexity of the active regions. They modulate the surface rotation through the Coriolis force, which accelerates or decelerates the fluid particles. They therefore offer a plausible explanation of the torsional oscillation pattern.There are a number of problems raised by such an unexpected circulation pattern: for example, the coexistence of axisymmeric rolls with hypothetical giant cells, the location of the dynamo source below or within the convective zone, and the coupling of the radiative interior and the convective layers. To resolve these important issues, continuous observational studies are needed of the manifestation of solar activity, as well as of radius and luminosity variations. So, we have aimed our paper at an audience of theoreticians in the hope that they take up the challenges we describe.

Observations and Modeling of North-South Asymmetries Using a Flux Transport Dynamo

“…Belucz & Dikpati (2013) focussed on global changes in meridional circulation, including amplitude changes of the whole circulation, differences between one and two cells in either latitude or depth. The meridional motions of sunspots, pores (Ribes & Bonnefond 1990, and their citations) and other magnetic features (Komm 1994;Meunier 1999) are related to generation of inflows. Observations by Gizon & Birch (2005) show that there are also significant meridional circulation patterns in the Sun that are not global, including one that is associated with ARs themselves.…”

The Effect of Activity-Related Meridional Flow Modulation on the Strength of the Solar Polar Magnetic Field

“…In the case of near-surface flows, the residual meridional flow velocities (after subtraction of the mean flow) during cycle 23 were of the order of ±3−5 m s −1 and converge toward the dominant latitudes of magnetic activity while migrating towards the equator in parallel to the activity belts (Gizon & Rempel 2008;González Hernández et al 2008, 2010. These flows are probably related to the meridional motions of sunspots and pores (Ribes & Bonnefond 1990, and references therein) and other magnetic features (Komm 1994;Meunier 1999). The cumulative effect of the near-surface horizontal flows converging towards active regions (e.g., Haber et al 2004;Hindman et al 2004) appear to contribute to the axisymmetric meridional flow perturbation (Gizon 2004;González Hernández et al 2008), but there is evidence that at least part of this perturbation is unrelated to surface activity (González Hernández et al 2010).…”

Solar Rotation over Solar Cycle 21

“…3. On the other hand, the zonal meridional circulation (north-south motions) for the whole data set is a direct measurement (Ribes and Bonnefond, 1990), see Fig. 4.…”