The influence of broken and inhomogeneous clouds on satellite cloud-phase retrievals is investigated. The research comprises two parts: First, an assessment of the effect of broken and inhomogeneous water clouds on the cloud-phase retrieval is performed through an evaluation of the errors in retrieved optical thickness (τ) and effective radius (reff) using synthetic datasets. Second, a comparison of MODIS low-resolution (3x3 km) cloud properties against corresponding high-resolution (1x1 km) retrievals for low-resolution cases of broken and inhomogeneous clouds was carried out. The evaluation of the synthetic datasets reveal that, for water clouds with high values of τ and reff, a shift in cloud phase from ‘water’ to ‘ice’ can be expected at cloud fractions between 0.4 and 0.8. For overcast fields of inhomogeneous water clouds, reff is overestimated by ~3-5 μm at low-resolution as compared to high-resolution. Depending on the amount of cloud variability and the underlying surface this overestimation may lead to a shift in cloud phase from ‘water’ to ‘ice’. Although the MODIS observations do not reveal a sharp increase in reff with decreasing cloud fraction, the expected increase in reff for inhomogeneous overcast water clouds is clearly manifested in the observations.
ELA Wolters, HM Deneke, JF Meirink, RA Roebeling. Impact of broken and inhomogeneous clouds in satellite cloud-phase retrieval
2008, 2008, EUMETSAT