Identifying cloud-free period is an important task as they are common references in cloud and aerosol radiative forcing studies. Their identification requires precise methods to distinguish condensed water from other aerosols (eg mineral or moist hydrophyle aerosols). In this study we combine analyses of wide field of view shortwave and longwave irradiances and lidar backscatter measurements to explore situations that are considered neither completely clear nor cloudy. We find that cloud-free periods detected by analysis of the broadband measurements are also identified as cloud free by the lidar in more than 60% of situations. Residual occurrences are composed of 90% high-altitude cirrus clouds, partitioned equally between subvisible and semi-transparent optical thickness classes.
Revised: September 3, 2008 |
Published: May 30, 2008
Citation
Dupont J., M. Haeffelin, and C.N. Long. 2008.Evaluation of cloudless-sky periods detected by shortwave and longwave algorithms using lidar measurements.Geophysical Research Letters 35, no. 10:Art. No. L10815.PNNL-SA-59793.doi:10.1029/2008GL033658