Unlocking potential: A case study on reducing shortwave radiation bias
in the Southern Ocean through improved cloud phase retrievals based on
machine learning
Abstract
There are significant gaps in both experimental and theoretical
understanding of mixed-phase clouds, their impacts on the hydrological
cycle as well as their effects on atmospheric radiation. Accurately
identifying liquid water layers in mixed-phase clouds is crucial for
estimating cloud radiative effects. A proof-of-concept study utilizing a
machine-learning-based liquid-layer detection method called VOODOO is
presented. This method was applied alongside a single-column radiative
transfer model to compare downwelling shortwave fluxes of mixed-phase
clouds detected by the standard Cloudnet processing chain and VOODOO to
ground-based pyranometer observations. Our findings reveal that VOODOO
creates more realistic liquid water content distributions and
significantly influences profiles of heating rates. Moreover, our study
demonstrates a substantial enhancement in the estimation of shortwave
cloud radiative effects of VOODOO compared to conventional method
Cloudnet. Specifically, we observe a remarkable reduction in the mean
absolute error of simulated shortwave radiation at the surface of
70\%, particularly in homogeneous cloud conditions. The
mean percentage error of SW cloud radiative effects between Cloudnet and
pyranometer observations is 44\%, while VOODOO+Cloudnet
reduces this error to 8\%. Overall, our results
underscore the potential of VOODOO to provide new insights into deep
mixed-phase clouds, which were previously inaccessible using traditional
lidar-based remote sensing techniques.