Stokes-meter observations of the solar mean magnetic field: Probable manifestations of strong small-scale magnetic fields

A paradox in measuring the magnetic field of the Sun

“…Information on methods of MMF measurement and the data can be found in Sherrer et al (1977aSherrer et al ( , 1977b, Kotov et al (1998aKotov et al ( , 1988b, Chaplin et al (2003), and Demidov et al (2005b). The WSO and KPO data were downloaded from the sites http://wso.stanford.edu and http://solis.nso.edu, respectively.…”

“…In this case, the nonlinear instrumental effects are a fortiori absent, so that a univocal correspondence should exist between p 0 and B with accuracy up to the δ -effect, random errors, and the effect of line-profile asymmetry (Demidov et al, 2005b). It would be specially noted that the MMF is determined by large-scale, i.e., background fields of the quiet Sun, while the contributions by sunspot and active-region fields are negligible (Severny, 1971;Kotov et al, 1977).…”

“…This is confirmed by five standard deviations S given in Table 1 Temporal variations in b can be caused by timedependent technical differences of the instruments and the dependence of the average values of |B| and/or the δ-effect on the solar-cycle phase. Within the framework of the fine-rope model, the latter can be related to the varying relative contribution of strong and weak fields to the total MMF signal (Demidov et al, 2002(Demidov et al, , 2005b, as well as to the evolution of the large-scale magnetic field distribution during a cycle. Accordingly, this can result in strengthening or weakening of the saturation during a cycle, whereas the saturation effect itself (Howard and Stenflo, 1972) is caused by strong fields resulting in such a line splitting, then the extremums of the Stokes parameter V in the line wings reach the output slits of the magnetograph or even go beyond.…”

“…However, it has been known for a long time that the results of measurements by different instruments in different lines differ strongly even for the "quiescent" photosphere outside active regions. The discrepancies are believed to be caused mainly by measurement errors and "saturation" of the magnetograph signals in magnetic rope-fibril-filament-fluxtube elements of the photosphere with angular widths less than an arcsecond with a strong magnetic field of about 1.0-1.5 kG, as well as by different temperature sensitivity of different lines (Howard and Stenflo, 1972;Stenflo, 1973;Demidov et al, 2002Demidov et al, , 2005aDemidov et al, , 2005b. In the case of measurements of the "local" fields in sunspots and active regions, additional discrepancies are caused by variations in the line profile and "expansion" of the solar magnetic fluxtubes with height in the solar atmosphere (Howard and Stenflo, 1972;Gopasyuk et al, 1973Gopasyuk et al, , 2000.…”

“…About 35 years ago, the main reason for discrepancies about the quiescent photosphere has been attributed to the superfine structure of the field, and the method of "magnetic field ratio," or δ -effect (measured using different lines), began to be widely used to interpret the magnetic measurements of the photosphere (Wang and Sheeley, 1995;Demidov et al, 2002Demidov et al, , 2005b. However, attention has been recently focused on quantitative discrepancies in the results by different authors who analyzed discrepancies in measurements by different instruments in different lines (Kotov, 2003).…”