The Harvard-Smithsonian reference atmosphere

We present a model of the solar atmosphere in the optical depth range from τ5000 = 10−8 to 25. It combines an improved model of the photosphere that incorporates recent EUV observations with a new model of the quiet lower chromosphere. The latter is based on OSO 4 observations of the Lyman continuum, on infrared observations, and on eclipse electron densities.Our model differs from the Bilderberg Continuum Atmosphere (BCA) in the low chromosphere (τ5000 < 10−4), where deviations from local thermodynamic equilibrium in hydrogen and carbon have been taken into account. It also differs in the transition region between the chromosphere and the photosphere (10−4 < τ5000 < 10−2), where the temperature is lower than in the BCA, and in the convective region (τ5000 ≳ 2), where the temperature is higher than in the BCA.

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