Using CALIOP to estimate cloud-field base height and its uncertainty: the Cloud Base Altitude Spatial Extrapolator (CBASE) algorithm and dataset

• Main Authors: J. Mülmenstädt, O. Sourdeval, D. S. Henderson, T. S. L'Ecuyer, C. Unglaub, L. Jungandreas, C. Böhm, L. M. Russell, J. Quaas
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-12-01
• Series: Earth System Science Data
• Online Access: https://www.earth-syst-sci-data.net/10/2279/2018/essd-10-2279-2018.pdf

<p>A technique is presented that uses attenuated backscatter profiles from the CALIOP satellite lidar to estimate cloud base heights of lower-troposphere liquid clouds (cloud base height below approximately 3&thinsp;km). Even when clouds are thick enough to attenuate the lidar beam (optical thickness <i>τ</i><i>≳</i>5), the technique provides cloud base heights by treating the cloud base height of nearby thinner clouds as representative of the surrounding cloud field. Using ground-based ceilometer data, uncertainty estimates for the cloud base height product at retrieval resolution are derived as a function of various properties of the CALIOP lidar profiles. Evaluation of the predicted cloud base heights and their predicted uncertainty using a second statistically independent ceilometer dataset shows that cloud base heights and uncertainties are biased by less than 10&thinsp;%. Geographic distributions of cloud base height and its uncertainty are presented. In some regions, the uncertainty is found to be substantially smaller than the 480&thinsp;m uncertainty assumed in the A-Train surface downwelling longwave estimate, potentially permitting the most uncertain of the radiative fluxes in the climate system to be better constrained. The cloud base dataset is available at <a href="https://doi.org/10.1594/WDCC/CBASE" target="_blank">https://doi.org/10.1594/WDCC/CBASE</a>.</p>