TY - JOUR

T1 - The spectral signature of cloud spatial structure in shortwave irradiance

AU - Song, Shi

AU - Sebastian Schmidt, K.

AU - Pilewskie, Peter

AU - King, D. Michael

AU - Heidinger, K. Andrew

AU - Walther, Andi

AU - Iwabuchi, Hironobu

AU - Wind, Gala

AU - Coddington, M. Odele

PY - 2016/11/8

Y1 - 2016/11/8

N2 - 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.

AB - 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.

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U2 - 10.5194/acp-16-13791-2016

DO - 10.5194/acp-16-13791-2016

M3 - Article

AN - SCOPUS:84995495543

SN - 1680-7316

VL - 16

SP - 13791

EP - 13806

JO - Atmospheric Chemistry and Physics

JF - Atmospheric Chemistry and Physics

IS - 21

ER -