The effect of non-coherency on the intensity of resonantly scattered sunlight in a planetary atmosphere

Abstract

Three frequency redistribution functions have been used in Monte Carlo calculations of the intensities due to resonance scattering of sunlight in an inhomogeneous atmosphere. The three functions used to describe the frequency change on scattering are (1) complete frequency redistribution (CFR), in which the scattered frequency is assumed independent of the initial frequency and has the same probability distribution as the absorption coefficient; (2) monochromatic radiative equilibrium (MRE), in which there is assumed to be no frequency shift in the frame of the observer; and (3) partial frequency redistribution (PFR), which is more precise than CFR or MRE since it is exact for an average scattering angle. The results apply mainly to the cores of saturated lines where Doppler broadening dominates over natural broadening. They confirm that in the core CFR yields results in very good agreement with those obtained with PFR. They also indicate that MRE yields reflected intensities only a few per cent high and intensities internal to the atmosphere no more than 30 per cent in error.