The Detection of Global Convection on the Sun by an Analysis of Line Shift Data of the John M. Wilcox Solar Observatory at Stanford University

Abstract

The first significant signatures of the real existence of the global convection in the Sun were found in the absorption line shift data of the John M. Wilcox Solar Observatory at Stanford University. The signatures consist of persistent periodic time variations in the east-west component of the velocity fields defined by fitting a slope to the line shift data in a certain longitude window at a specified latitude and longitude by a least square method. The variations show that the amplitude of the velocity fields is on the order of 100 m/s. The spacial structure of the east-west flows on the visible hemisphere of the Sun propagates along with the rotation of the Sun at a slightly slower speed than that of the Sun at the equator. The structure extends across the equator as predicted by theory. The periodicity of the time variation indicates that the wave numbers of the structure are 7 and 5 in Septembers of 1979 and 1981 with faster propagation velocity for the larger wave number during these two time intervals, when clear signals of the global convection were found. This implies that several modes of the global convection are coexisting in the solar convection zone. A personal account of the analysis and its interpretation are given.

National Academy of Sciences / National Research Council Senior Resident Research Associate on leave of absence from Department of Astronomy, University of Tokyo.