Cloud edges: the spectral-invariant relationship between ratios of zenith radiances near them
Poster PDF
Authors
Warren J. Wiscombe — Brookhaven National Laboratory
Alexander Marshak — NASA - Goddard Space Flight Center
Yuri Knyazikhin — Boston University
J.-Y. Christine Chiu — Colorado State University
Description
The transition zone between cloudy and cloud-free areas is where strong aerosol-cloud interactions take place. We have discovered a surprising spectral-invariant relationship between ratios of zenith radiance spectra measured by the ARM shortwave spectrometer (SWS) in this transition zone. This relationship demonstrates, as a consequence, that the shortwave spectrum within the transition zone is fully determined by zenith radiance spectra of fully cloudy and fully cloud-free regions. We also report the results of radiative transfer calculations that confirm the spectral invariance and show how the spectral-invariant relationship is affected by factors such as cloud thermodynamic phase, underlying surface types, aerosol properties, and the finite field-of-view of the spectrometer. Finally, we illustrate the dependence of spectral-invariant characteristics of the transition zone on aerosol properties using measurements from the AMF two-channel narrow field-of-view radiometer (2NFOV).
