Dissertation/Thesis Abstract

The Spectral Signature of Cloud Spatial Structure in Shortwave Radiation
by Song, Shi, Ph.D., University of Colorado at Boulder, 2016, 158; 10151129
Abstract (Summary)

In this thesis, we aim to systematically understand the relationship between cloud spatial structure and its radiation imprints, i.e., three-dimensional (3D) cloud effects, with the ultimate goal of deriving accurate radiative energy budget estimates from space, aircraft, or ground-based observations under spatially inhomogeneous conditions. By studying the full spectral information in the measured and modeled shortwave radiation fields of heterogeneous cloud scenes sampled during aircraft field experiments, we find evidence that cloud spatial structure reveals itself through spectral signatures in the associated irradiance and radiance fields in the near-ultraviolet and visible spectral range.

The spectral signature of 3D cloud effects in irradiances is apparent as a domain- wide, consistent correlation between the magnitude and spectral dependence of net horizontal photon transport. The physical mechanism of this phenomenon is molecular scattering in conjunction with cloud heterogeneity. A simple parameterization with a single parameter ϵ is developed, which holds for individual pixels and the domain as a whole. We then investigate the impact of scene parameters on the discovered correlation and find that it is upheld for a wide range of scene conditions, although the value of ϵ varies from scene to scene.

The spectral signature of 3D cloud effects in radiances manifests itself as a distinct relationship between the magnitude and spectral dependence of reflectance, which cannot be reproduced in the one-dimensional (1D) radiative transfer framework. Using the spectral signature in radiances and irradiances, it is possible to infer information on net horizontal photon transport from spectral radiance perturbations on the basis of pixel populations in sub-domains of a cloud scene.

We show that two different biases need to be considered when attempting radiative closure between measured and modeled irradiance fields below inhomogeneous cloud fields: the remote sensing bias (affecting cloud radiances and thus retrieved properties of the inhomogeneous scene) and the irradiance bias (ignoring 3D effects in the calculation of irradiance fields from imagery-based cloud retrievals). The newly established relationships between spatial and spectral structure lay the foundation for first-order corrections for these 3D biases within a 1D framework, once the correlations are explored on a more statistical basis.

Indexing (document details)
Advisor: Schmidt, Konrad Sebastian
Commitee: Feingold, Graham, King, Michael, Pilewskie, Peter, Randall, Cora, Toon, Brian
School: University of Colorado at Boulder
Department: Atmospheric and Oceanic Sciences
School Location: United States -- Colorado
Source: DAI-B 78/03(E), Dissertation Abstracts International
Subjects: Atmospheric sciences, Remote sensing
Keywords: 3D cloud effects, Accurate radiative energy budget estimates, Cloud spatial structure, Radiation imprints
Publication Number: 10151129
ISBN: 978-1-369-05893-2
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