New measurements of magnetic field of the Sun-as-a-star: Observations at the Sayan Observatory in 1993-1997

A currently central experimental problem in modern helio-physics is that of measuring global parameters of the Sun. One such parameter, characterizing the Sun as a magnetically variable star, is the mean (general) magnetic field (MMF). Unfortunately, in recent years J.Wilcox Solar Observatory (WSO) at Stanford University has been the only observatory doing regular solar MMF (SMMF) measurements. However, to judge in an unbiased manner the reliability of SMMF observations and results obtained on their basis, it seems appropriate and very useful to compare different observational sequences. Towards this end, an analysis is made of observational data on SMMF obtained with the STOP telescope at Sayan Solar Observatory (SSO) during 1993-1997, or the declining phase of the 22nd activity cycle. During that time interval, after the STOP equipment was step-wise modernized, it was possible to improve significantly the accuracy and reliability of data, as well as to ensure their reasonably high regularity. Correlation and regression analyses of SMMF observations from WSO and SSO showed a very good agreement of the two observational series from 1993 and 1994 and a somewhat poorer agreement for 1995-1997. A certain decrease in correlation is most likely to be caused by a significant fall in SMMF strength during 1995-1997 corresponding to minimum solar activity and, as a consequence, by an increase in the influence of instrumental effects. The paper gives a discussion of some of such effects, as well as of main procedural features of SMMF observations at WSO and SSO.