Optimal estimation of optical properties of mixed phase Arctic clouds observed from a tethered balloon platform

Clouds play an important role in the radiation budget of polar regions and mixed phase clouds are prevalent in the Arctic. These mixed phase clouds, consisting of ice crystals and liquid water droplets, are important to understand climate change in the Arctic. A unique observational study using a tethered balloon system was conducted in Ny-Alesund, Norway, located high in the Arctic at 78.9°N and 11.9°E, in May--June 2008 to collect radiometric and microphysical data of mixed phase clouds. A reliable knowledge of cloud microphysical and radiative properties is important to improve the accuracy of climate predictions. This research addresses the challenge associated with the estimation of cloud optical properties that are required in climate models. An accurate radiative transfer model is used to simulate radiative quantities including mean intensities and irradiances that can be compared directly to the corresponding observed quantities. Analyses of the unique vertical profiles of boundary layer mixed phase clouds observed in the Arctic demonstrate that cloud layering has little impact on the downward irradiance at the surface as long as the total optical depth remains unchanged. In contrast, the mean intensity estimated from the irradiances measured by the radiometer deployed on the balloon depends upon the vertical cloud structure and was used to quantify the partitioning between ice and liquid water. This research also reflects on some of the latest advancements in the analysis of data related to Earth's radiation budget and our understanding of climate change and global warming.