Dipolar and Quadrupolar Magnetic Field Evolution over Solar Cycles 21, 22, and 23

Abstract

Abstract. Time series of photospheric magnetic field maps from two observatories, along with data from an evolving surface-flux transport model, are decomposed into their constituent spherical harmonic modes. The evolution of these spherical harmonic spectra reflect the modulation of bipole emergence rates through the solar activity cycle, and the subsequent dispersal, shear, and advection of magnetic flux patterns across the solar photosphere. In this article, we discuss the evolution of the dipolar and quadrupolar modes throughout the past three solar cycles (Cycles 21-23), as well as their relation to the reversal of the polar dipole during each solar maximum, and by extension to aspects of the operation of the global solar dynamo.

Geomagnetic detection of the sectorial solar magnetic field and the historical peculiarity of minimum 23–24

“…Figure 4a is related to plots of dipole tilt seen in many papers, and it is equivalent to Hoeksema [2009], his Figure 2c divided by his Figure 2a. Otherwise, the sectorial quadrupole energy shown in Figure 4b is different from that shown in other work (contrast with Abramenko et al [2010, Figure 5] and DeRosa et al [2010, Figure 4]).…”

“…These same harmonics have been identified in geomagnetic activity and thermospheric density [ Lei et al , 2008; Thayer et al , 2008], in auroral electrons [ Emery et al , 2009], and in relativistic radiation belt electrons [ Gibson et al , 2009], each for years near minimum 23–24. These observations have been interpreted in terms of low‐latitude coronal holes [ de Toma , 2012] and multipolar ingredients in the solar magnetic field [ Abramenko et al , 2010; DeRosa et al , 2010] that gave structural complexity to the heliospheric current sheet [ McComas et al , 2006; Hathaway and Suess , 2008].…”

Anelastic spherical dynamos with radially variable electrical conductivity

“…These stars are substantially more massive than the Sun ( M > 1.5 M ) hence they are convectively unstable in the core and stably stratified in the radiative outer region, which is known to develop differential rotation ( Triana et al, 2015 ). Further the quadrupolar magnetic moment of the Sun can be substantial at periods during the solar cycle, and was suggested to dominate over the axial and equatorial dipole components at the time of grand solar minima ( Knobloch et al, 1998;Beer et al, 1998;DeRosa et al, 2011 ). The magnetic fields of the ice giants are best described with a strong contribution from the equatorial dipole mode ( Holme and Bloxham, 1996;Stanley and Bloxham, 2004 ).…”