1. Large-Scale Solar Magnetic Fields – How is Solar Cycle 24 Different?
SH31B-2549
Dipole and other Large-scale Solar Magnetic Field Parameters:
HCS “Tilt’’ Dipole Components Di- Quad- Octo-pole Axial (m=0) Comp.
Total Dipole
Polar
Equatorial
HCS Maximum Latitude
Octopole
Quadrupole
> 2016
J. Todd Hoeksema, Stanford University
Solar Cycle 24 has been relatively quiet compared to the last several Solar Cycles. Since its late onset, solar activity has been more asymmetric between north and south.
The northern polar field reversed tentatively earlier, but lingered near 0; the south reversed more definitively, but is now weakening. The north is now strengthening due to increased activity late in the cycle.
Zonal averages of the field show how magnetic flux that originates in active regions moves poleward. A few active regions contribute much of the flux that reaches the poles.
The dipole is about as strong as it was during weak Cycle 23. As in Cycle 23, the weak polar field allows the heliospheric current sheet to reach higher latitude. If new activity does not increase the polar field strength, Cycle 25 is likely to be no stronger than Cycle 24.
The heliosphere responds to the photospheric and coronal field configuration and evolves differently depending on the strength of the dipole and other large-scale field components.
Zonal Averages of the magnetic field from 1976 to the present (WSO). Bottom panel is the familiar ‘butterfly’ diagram of total flux vs time. Next panel shows the net flux for each solar rotation vs latitude and time. Flux emerges in active regions in each cycle and the unbalanced flux that does not cancel makes its way poleward to reverse and strengthen the polar caps. The top two panels show the symmetric and antisymmetric components of the net flux.
Close-up net zonal flux maps from HMI show how polarity patterns move poleward in surges in Cycle 24.
Polar Field above 55◦ from WSO –
Polar Field above 60◦ from HMI –
(X. Sun, M. Bobra - hmi.stanford.edu/magnetic)
North-South Asymmetry in Solar Activity
Sunspot Number – Solar Cycles
Cycle 21 ( ) Cycle 22 ( ) Cycle 23 ( ) Cycle 24 ( )
Evolving configuration of the computed Heliospheric Current Sheet for Solar Cycles 21 – 24 (1976 – 2016) at 6 CR (~month) intervals
The HCS progresses from equatorial to azimuthal during the rise of the cycle, then slowly relaxes after the polar field reversal. Cycle 24 was slower and weaker. Poles only strengthen in 2014