On the apparent velocity of integrated sunlight. I - 1983-1985

The authors have measured absolute frequencies for the ΔV = 2 transitions of 12C16O in the 2.3 μm spectrum of integrated sunlight. The data consist of 78 interferograms taken over a 3 yr period with the McMath Fourier transform spectrometer on Kitt Peak. The spectra cover the 4000 - 4800 cm-1 region with 0.012 cm-1 resolution. At a given epoch, the absolute velocity of integrated sunlight were obtained with an uncertainty of ⪉5 m s-1. The authors find that the integrated light velocity varies by ⪉3 m s-1 over a 1 day period, consistent with expectations based on the properties of supergranulation. Over the long term, the data indicate an increasing blueshift in these weak infrared lines, amounting to 30 m s-1 from 1983 through 1985. The sense of the drift is consistent with a lessening in the magnetic inhibition of granular convection at solar minimum.