Validation of a New Cloud Layer Detection Method
Cloud vertical structure, a key parameter affecting the impact of clouds on Earth’s energy balance, is among the most difficult atmospheric quantities to observe. Operational long-term measurements of cloud vertical structure are only available from remote-sensing measurements made at a few ground sites around the world, such as the U.S. Department of Energy’s (DOE) Atmospheric Radiation Measurement (ARM) sites. However, radiosondes are routinely launched for meteorological observations around the world, and their information on temperature and humidity profiles can be used to derive information on cloud vertical layers. DOE scientists have now developed a new method to detect cloud layers from radiosonde data. The method was rigorously evaluated using multiple years of radar measurements from the ARM sites. Overall, the location of cloud layers derived from radiosonde and cloud radar measurements agree reasonably well. Some near-surface cloud layers were classified as cloud layers by the radar but as clear from radiosonde measurements; a few cloud layers at high altitudes were detected by the radiosonde but missed by the cloud radar. Absolute differences in cloud-base heights and cloud-top heights from radiosonde and cloud radar matched retrievals at the ARM Southern Great Plains (SGP) site were less than 500 m for 86% and 79% of the cases analyzed, respectively. The large differences between cloud boundaries from the two retrieval methods are mostly due to balloon drift, resulting in the radiosonde sampling different parts of the cloud field than the vertically pointing radars. Application of the new method to radiosonde datasets from around the world will increase the available information on cloud vertical structure, which will be useful for understanding cloud impacts on the radiation budget and for evaluation of cloud structure in climate models.
Zhang, J., Z. Li, H. Chen, and M. Cribb. 2013. “Validation of a Radiosonde-Based Cloud Layer Detection Method Against a Ground-Based Remote Sensing Method at Multiple ARM Sites,” Journal of Geophysical Research: Atmospheres 118(2), 846—58. DOI: 10.1029/2012JD018515.