Continental stratus clouds: A case study using coordinated remote sensing and aircraft measurements

A continental stratus cloud layer was studied by advanced ground-based remo te sensing instruments and aircraft probes on 30 April 1994 from the Cloud and Radiation Testbed site in north-central Oklahoma. The boundary layer st ructure clearly resembled that of a cloud-topped mixed layer, and the cloud content is shown to be near adiabatic up to the cloud-top entrainment zone . A cloud retrieval algorithm using the radar reflectivity and cloud drople t concentration (either measured in situ or deduced using dual-channel micr owave radiometer data) is applied to construct uniquely high-resolution cro ss sections of liquid water content and mean droplet radius. The combined e vidence indicates that the 350-600 m deep, slightly supercooled (2.0 degree s to -2.0 degrees C) cloud, which failed to produce any detectable ice or d rizzle particles, contained an average droplet concentration of 347 cm(-3), and a maximum liquid water content of 0.8 g m(-3) and mean droplet radius of 9 mu m near cloud top. Lidar data indicate that the K-a-band radar usual ly detected the cloud-base height to within similar to 50 m, such that the radar insensitivity to small cloud droplets had a small impact on the findi ngs. Radar-derived liquid water paths ranged from 71 to 259 g m(-2) as the stratus deck varied, which is in excellent agreement with dual-channel micr owave radiometer data, but similar to 20% higher than that measured in situ . This difference appears to be due to the undersampling of the few largest cloud droplets by the aircraft probes. This combination of approaches yiel ds a unique image of the content of a continental stratus cloud, as well as illustrating the utility of modern remote sensing systems for probing nonp recipitating water clouds.