Background magnetic fields during last three cycles of solar activity

Abstract

This paper describes our studies of evolution of the solar magnetic field with different sign and field strength in the range from -100 G to 100 G. The structure and evolution of large-scale magnetic fields on the Sun during the last 3 cycles of solar activity is investigated using magnetograph data from the Kitt Peak Solar Observatory. This analysis reveals two groups of the large-scale magnetic fields evolving differently during the cycles. The first group is represented by relatively weak background fields, and is best observed in the range of 3-10 Gauss. The second group is represented by stronger fields of 75-100 Gauss. The spatial and temporal properties of these groups are described and compared with the total magnetic flux. It is shown that the anomalous behaviour of the total flux during the last cycle can be found only in the second group

Positive and Negative Photospheric Fields in Solar Cycles 21–24

“…If we consider the whole hemisphere, the percentage is about 60% (see Figure 3a). Two characteristic groups of the large-scale magnetic fields were described by Andryeyeva and Stepanian (2008): the first group represented weak background fields 3 − 10 G, the second group represented stronger fields 75 − 100 G. It was shown that weak fields with the N-polarity in the northern hemisphere correlate with the S-polarity fields in the southern hemisphere. This result is in good agreement with Figure 5.…”

“…The distribution of magnetic fields over the surface of the Sun and its change in the course of the solar cycle is one of the key points in creating of the solar dynamo models (see, for example, Charbonneau, 2010). Evolution of zonal distribution of the Sun's magnetic field was considered by Hoeksema (1991) on the basis of magnetograms of the Wilcox Solar Observatory (WSO). It was shown that the magnetic flux is closely connected to the level of activity and is similar to the Maunder butterfly diagram which reflects the distribution of sunspots.…”

“…The dipole character of the global field is manifested in the defining role of the dipole moment among coefficients of the magnetic field multipole expansion according to the PFSS model (the potential-field source-surface model (Hoeksema and Scherrer, 1986)). The dominating terms of the expansion are the dipole, hexapole, and quadrupole, the main field components during minima of SA being the axial ones (Bravo and González-Esparza, 2000). While the dipole and hexapole have opposite polarities at the Sun's poles, the quadrupole has the same sign at both poles.…”