CLOUD BOUNDARY STATISTICS DURING FIRE-II

An 8-mm wavelength radar, 3-mm wavelength radar, and 10.6-mu m wavelen gth lidar operated side by side in vertically pointing mode during the First ISCCP Regional Experiment (FIRE II). This data collection mode yielded detailed information on distribution of cloud and cloud bounda ries as a function of altitude. Statistics on the location of cloud bo undaries during the FIRE II experiment indicate that cloud bases tende d to form at two discrete levels centered around 2.5 and 7.5 km, cirru s cloud tops formed most frequently at 9.5 km, and cloud thicknesses w ere usually 2 km or less. The atmosphere had the highest incidence of cloudiness at 8.5 km AGL, with a secondary maximum at an altitude of 3 .5 km AGL. The incidence of cloudiness fell off rapidly between 8 and 11 km; there was also a distinct minimum in cloudiness at 2 km AGL. Th e diumal variation of upper-level cloud base and top heights was about 1.0 km AGL, with the highest bases and tops occurring at 0500 UTC and the lowest bases and tops occurring at 1500 UTC. Co-occurring cloud l ayers (two or more simultaneous layers) were common, with the conditio n of a single cloud layer accounting for only 40% of the observation p eriod.