Observations of cloud properties in cloudy-to-clear transition zones during MAGIC field campaign
Authors
Alexander Marshak — NASA - Goddard Space Flight Center
Weidong Yang — Universities Space Research Association
Patrick McBride — Atmospheric and Space Technology Research Associates (ASTRA)
J.-Y. Christine Chiu — Colorado State University
Yuri Knyazikhin — Boston University
Sebastian Schmidt — University of Colorado, Boulder
Connor J. Flynn — University of Oklahoma School of Meteorology
Ernie R. Lewis — Brookhaven National Laboratory
Category
General topics – Clouds
Description
The time-resolved hyperspectral measurements from SSFR (Solar Spectral Flux Radiometer) and SASZe (Shortwave Array Spectroradiometer-Zenith) during MAGIC (Marine ARM GPCI Investigation of Clouds) field campaign provide a unique opportunity to study cloud properties such as optical thickness and effective radius in the transition zone between cloudy and clear sky air. The measurements from the SSFR and the SASZe are different in values, however we found that inter-instrument differences between self-normalized measurements (divided by their own spectra at a fixed time) are small. In this study, cloud properties are analyzed using the spectrally invariant technique developed earlier by our group. This technique approximates the spectra in the cloud-clear transition zone as a linear combination of definitely clear and definitely cloudy spectra; the coefficients of the linear approximation, slope and intercept, characterize the spectrally invariant cloud properties in the transition zone. Simulations with the SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model demonstrate that (1) the slope in the visible spectral band is well correlated with cloud optical thickness while the intercept of the near-infrared spectral band has a high negative correlation with cloud drop effective radius even without the exact knowledge of optical thickness; (2) The above relations hold for all solar angles and for cloud contaminated skies. Analyzing SSFR and SASZe observations, we found that during cloudy-to-clear transitions (a) the slopes of the visible band decrease towards cloud edges while (b) the intercepts of the near-infrared band remain almost constant near cloud edges. These findings suggest that, while the optical thickness decreases during cloudy-to-clear transition, the cloud drop effective radius does not change approaching cloud edges. These results support the hypothesis that inhomogeneous mixing dominates near cloud edges.
