Solar wind speed and He I (1083 nm) absorption line intensity

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Abstract
Since the pattern of the solar wind was relatively steady during Carrington rotaions 1748 through 1752 in 1984, an average distribution of the solar wind speed on a so‐called “source surface” can be constructed by superposed epoch analysis of the wind values estimated by the interplanetary scintillation observations. The average distribution of the solar wind speed is then projected onto the photosphere along magnetic field lines computed by a so‐called “potential model” with the line‐of‐sight components of the photospheric magnetic fields. The solar wind speeds projected onto the photosphere are compared with the intensities of the He I (1083 nm) absorption line at the corresponding locations in the chromosphere. We found that there is a linear relation between the speeds and the intensities. Since the intensity of the He I (1083 nm) absorption line is coupled with the temperature of the corona, this relation suggests that some physical mechanism in or above the photosphere accelerates coronal plasmas to the solar wind speed in regions where the temperature is low. Further, it is suggested that the efficiency of the solar wind acceleration decreases as the coronal temperature increases.