The Interaction of New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23

Abstract

The 11-year cycle of solar activity follows Hale's law by reversing the magnetic polarity of leading and following sunspots in bipolar regions during the minima of activity. In the 1996-97 solar minimum, most solar activity emerged in narrow longitudinal zones -'active longitudes' but over a range in latitude. Investigating the distribution of solar magnetic flux, we have found that the Hale sunspot polarity reversal first occurred in these active zones. We have estimated the rotation rates of the magnetic flux in the active zones before and after the polarity reversal. Comparing these rotation rates with the internal rotation inferred by helioseismology, we suggest that both 'old' and 'new' magnetic fluxes were probably generated in a low-latitude zone near the base of the solar convection zone. The reversal of active region polarity observed in certain longitudes at the beginning of a new solar cycle suggests that the phenomenon of active longitudes may give fundamental information about the mechanism of the solar cycle. The nonrandom distribution of old-cycle and new-cycle fluxes presents a challenge for dynamo theories, most of which assume a uniform longitudinal distribution of solar magnetic fields.

Global analysis of active longitudes of sunspots

“…It has been found that various manifestations of solar activity, such as sunspots (Berdyugina et al 2003;Usoskin et al 2005;Juckett 2006), solar magnetic field (Benevolenskaya et al 1999;Bumba et al 2000), heliospheric magnetic field (Ruzmaikin et al 2001;Takalo & Mursula 2002;Mursula & Hiltula 2004), and flares (Bai 1988(Bai , 2003 occur preferentially at specific longitudes that are called active longitudes. However, lifetimes and rotation velocities of active longitudes obtained for different tracers of solar activity have been found to vary significantly.…”

Active Longitudinal Structures of the Sun from MDI and EIT Observations

“…Examples of EIT synoptic maps for 171A, 195A, 284A and 304A for CR1935 are presented in Figure 1. (Benevolenskaya et al 1999). However, the large-scale stable longitudinal patterns are better seen on the coronal maps than on the magnetic maps.…”

“…Studying rotation of the 'old' and 'new' fluxes and comparing their rotation rates with the internal rotation obtained by helioseismology we have suggested that both fluxes are probably generated in a narrow low-latitude zone of the tachocline (Benevolenskaya et al 1999) -the region of the steep radial gradient of solar rotation at the bottom of the convection zone, where the magnetic flux is probably generated (e.g. Parker, 1993).…”

“…However, the large-scale stable longitudinal patterns are better seen on the coronal maps than on the magnetic maps. During this period the magnetic structure of the Sun was determined by the interaction between the 'old' and 'new' magnetic fluxes: the 'old' flux was concentrated in two active longitudinal zones, and most of the initial 'new' flux emerged in the same zones (Benevolenskaya et al, 1999).…”

Advances in Theory and Simulations of Large-Scale Dynamos

“…This led to the now popular idea of flux-transport dynamos where the meridional circulation is chiefly responsible for the equatorward migration of the toroidal flux belts (see article by M. Dikpati in this issue). However, in recent years it became clear that in the outer 5% of the Sun by radius there is strong negative radial shear (Benevolenskaya et al 1999), which could in principle also explain the equatorward migration in the framework of conventional solar dynamo theory (B05). On the other hand, such a theory also faces problems of its own, for example the latitudinal width of the flux belts is expected to be only a few times bigger than the depths of the supergranulation layer ), which would be too small.…”