Mean line bisector positions were found for the neutral iron line at 25250.2 using disk-integrated sunlight. After correction for the apparent time variation of the instrumental profile, it was found that the mean bisector position was constant during the period from May 1982 to February 1983. The correlation between the total magnetic flux as measured at Mount Wilson and the line asymmetry results of Livingston is not high. In particular, the magnetic flux dropped in 1982, suggesting a large line asymmetry that was not observed. However, the correlation between the 30-day average of the mean magnetic field and Livingston's results is quite high (-0.95), suggesting that the asymmetry of the disk-integrated line profile is related to the old plage regions rather than to the active regions.
I. Introduction
Line profiles were first observed to be asymmetric by Higgs (1960Higgs ( , 1962) ) in her interferometric study of the solar limb red-shift. Many studies of the line asymmetry have followed and it is fairly well known that the asymmetry is caused by the superposition of many different Doppler shifts in convective cells (Beckers and Nelson, 1978;Nordlund, 1980). The weighting of the upward and downward motions by their respective temperatures and intensities results in a line profile that is asymmetric. Although most studies of line asymmetry have concentrated on the interpretation of the convective shifts and possible effects of waves on the line shape, Livingston (1982) has searched for possible time variations in the line asymmetry.
Livingston (1982, 1983) reported that the asymmetry of the neutral iron line at 2 5250.6 A varies with time. From 1976 to 1982, the line bisector became less C-shaped and the mean line bisector position shifted redward. In particular, the bisector curvature (defined as the distance from line minimum to the point of maximum bisector curvature) changed nearly linearly from a value of 2.95 m* in mid-1980 to a value of 2.72 m]~ in mid-1982. This corresponds to a change in the mean line bisector position of 3 m s -1 yr-1 redward (roughly one-half the change of the bisector curvature).
To help determine the reason for this change, Livingston (1982) observed the magnetically sensitive 2 5250.6 line inside and outside a magnetic region on the Sun.