Average photospheric poloidal and toroidal magnetic field components near solar minimum

Abstract

Average (over longitude and time) photospheric magnetic field components are derived from 3′ Stanford magnetograms made near the solar minimum of cycle 21. The average magnetograph signal is found to behave as the projection of a vector for measurements made across the disk. The poloidal field exhibits the familiar dipolar structure near the poles, with a measured signal in the line Fe i λ 5250 A of ≈ 1 G. At low latitudes the poloidal field has the polarity of the poles, but is of reduced magnitude (≈ 0.1 G). A net photospheric toroidal field with a broad latitudinal extent is found. The polarity of the toroidal field is opposite in the nothern and southern hemispheres and has the same sense as subsurface flux tubes giving rise to active regions of solar cycle 21.