NASA's Airborne Field Mill (ABFM) experiments at Kennedy Space Center (KSC) in 2000 and 2001 were designed to study cloud electrification processes and to assess various lightning launch commit criteria (LLCC) regulations. In February 2001, the experiment included observations by a scanning 35-GHz cloud radar from NOAA's Environmental Technology Laboratory (ETL) to augment data from the project's cloud physics aircraft, ground-based electric field mill network, and operational weather surveillance radar. This Ka-band radar has excellent sensitivity and provides high-resolution (37-m) measurements of the structure and kinematics of nearby non-precipitating and weakly precipitating clouds. Its role in the ABFM was to provide a clearer context for interpreting the aircraft and field mill network data and to assess the cloud information content of the permanent weather surveillance radar that is routinely used as part of KSC launch commit decisions.

On 03FEB01 the University of North Dakota Citation research aircraft took off to investigate clouds over KSC, based on the ETL radar observations. The radar revealed a stratiform cloud layer, approximately 2 km thick, that extended upward to the -5 C altitude at 4.5 km MSL. As such, the cloud violated the LLCC "thick cloud" rule. (To paraphrase, this rule prohibits rocket launches, for fear of triggered lightning strikes, if a cloud is present that is more than 4500 ft thick and any part of it is within the 0 to -20 C temperature interval). As the cloud radar conducted RHI scans to document in detail the cloud's vertical structure, the aircraft made numerous penetrations overhead between -5 C and +1C. Drizzle fell at times during the 2-hour flight. Although the cloud never extended much above the -5 C level, it produced plentiful small ice crystals and some centimeter-size ice particles, according to the aircraft probe measurements. A melting layer bright band was also plainly evident in the cloud radar scan images. Thus, an ice process was definitely operating. Nevertheless, no natural lightning was detected anywhere in the area, and the airborne and ground-based field mills measured only weak (< 0.5 kv/m) electric fields within and beneath the cloud, suggesting a minimal threat of triggered lightning. Therefore, this case is one example where the thick cloud rule was overly restrictive.

Data from the 03FEB01 case are examined in this article with special emphasis on comparisons between the visiting high-resolution cloud radar observations and those of the permanent, coarser resolution weather surveillance radar. Similar comparisons for much weaker clouds on 13FEB01 are also presented.