Abstract
Observations of helium 10,830-A radiation with a grille spectrometer at Socorro, New Mexico, from 1967 to 1970 are presented. The data are discussed in light of new computations of the excitation and emission profiles. The observational data show an intensity increase of a factor of 3 during this period that is closely related to a corresponding change in the solar EUV radiation (λ<380 A). A large seasonal variation is discussed that is caused in part by a 5∶1 variation in the neutral helium abundance and that is augmented by seasonal variation in the conjugate photoelectron flux. In addition, a diurnal variation of the helium abundance of about 30% with a maximum in the morning is suggested.
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