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North Carolina State University: "Nowcasting convective activity during space shuttle launches and landings"

Final Report

This project was the first Outreach project sponsored by the Air Force. The primary objective was to improve the lead time and accuracy of forecasting the onset of convective activity (particularly during easterly flow regimes) at the Kennedy Space Center (KSC) and Cape Canaveral Air Station (CCAS). Topics investigated included the role of Rayleigh-Bernard instability in the boundary layer and how it helps to act as a trigger of convection, as well as the roles of conditional symmetric instability, conditional instability of the second kind, and inflection point instability for furthering the development of convection above the boundary layer. Evaluation of large-scale forcings were conducted in conjunction with utilization of satellite imagery to document the moisture distribution over the ocean area and its impact on convective activity. Finally, the Mesoscale Atmospheric Simulation System (MASS) model was used to simulate moisture, kinematic, and stability parameters over the Florida peninsula and to assess their applicability to forecasting convective activity.

Four days of onshore flow during the CAPE experiment (1991) were analyzed, including two active, one passive, and one suppressed convective day at KSC/CCAS. A careful regional analysis that included Global Optimal Interpolation data as a first guess field and 20 m height contouring at 150 mb uncovered several distinctions between the four days. Rawinsonde observations, the regional analysis, and numerical simulations all supported the suggestion that transverse circulations associated with the upper tropospheric jet streak distinguish the active and passive days. In conjunction with enhanced regional analysis and numerical model output, the good spatial and temporal resolution of the satellite observations represent a key resource for predicting the location and timing of convection during easterly flow regimes.

Analysis of sounding data showed elevated moisture above the marine boundary layer on convectively active days. Consequently, only the K stability index, which references 700 mb moisture, was found to have modest utility in discriminating convective activity in the vicinity of KSC. Given the critical importance of the water vapor distribution in forecasting convection, it is interesting to consider the potential improvements to forecasting with the addition of water vapor observations derived from the Global Positioning System.