The spectral signature of cloud spatial structure in shortwave irradiance

Shi Song, K. Sebastian Schmidt, Peter Pilewskie, D. Michael King, K. Andrew Heidinger, Andi Walther, Hironobu Iwabuchi, Gala Wind, M. Odele Coddington

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


In this paper, we used cloud imagery from a NASA field experiment in conjunction with three-dimensional radiative transfer calculations to show that cloud spatial structure manifests itself as a spectral signature in shortwave irradiance fields – specifically in transmittance and net horizontal photon transport in the visible and near-ultraviolet wavelength range. We found a robust correlation between the magnitude of net horizontal photon transport (H) and its spectral dependence (slope), which is scale-invariant and holds for the entire pixel population of a domain. This was surprising at first given the large degree of spatial inhomogeneity. We prove that the underlying physical mechanism for this phenomenon is molecular scattering in conjunction with cloud spatial structure. On this basis, we developed a simple parameterization through a single parameter μ, which quantifies the characteristic spectral signature of spatial inhomogeneities. In the case we studied, neglecting net horizontal photon transport leads to a local transmittance bias of ±12–19ĝ€%, even at the relatively coarse spatial resolution of 20ĝ€km. Since three-dimensional effects depend on the spatial context of a given pixel in a nontrivial way, the spectral dimension of this problem may emerge as the starting point for future bias corrections.

Original languageEnglish
Pages (from-to)13791-13806
Number of pages16
JournalAtmospheric Chemistry and Physics
Issue number21
Publication statusPublished - 2016 Nov 8


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