A three-dimensional radiative transfer model to investigate the solar radiation within a cloudy atmosphere. Part 2: Spectral effects
- Univ. of California, Santa Barbara, CA (United States)
In this second part of a two-part paper, the spectral response of the interaction between gases, cloud droplets, and solar radiation is investigated using a Monte Carlo-based three-dimensional (3D) radiative transfer model with a spectral resolution of 0.005 {micro}m. Spectrally resolved albedo at the top of the atmosphere, transmission to the surface, and absorption throughout the atmospheric column between 0.25 and 4.0 {micro}m are computed and compared for 3D and independent pixel approximations at various solar zenith angles. Analysis of a topical cloud field shows that for overhead sun, the effects of cloud morphology reduce absorption in the UV and increase absorption in the water-vapor absorption bands. At steep solar zenith angles, the enhanced absorption shifts spectrally to the near-infrared atmospheric windows, where increases up to 50% in absorption by cloud droplets are obtained. While there is no change in absorption in the visible, the 3D effect is shown to produce false estimates of cloudy-column absorption based on residual net fluxes in this spectral region. Alterations to the albedo and enhanced absorption in the 3D computations generate reduced estimates in remotely sensed cloud optical thickness and overestimates in cloud-droplet size distribution. Finally, a band ratio of 0.94 to 1.53 {micro}m downwelling irradiance at the surface is proposed as a possible measure of 3D enhanced atmospheric absorption.
- Sponsoring Organization:
- USDOE, Washington, DC (United States); National Science Foundation, Washington, DC (United States); National Aeronautics and Space Administration, Washington, DC (United States)
- OSTI ID:
- 659012
- Journal Information:
- Journal of the Atmospheric Sciences, Vol. 55, Issue 19; Other Information: PBD: 1 Oct 1998
- Country of Publication:
- United States
- Language:
- English
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