Cloud Altitude Determination of Overshooting Tops in Severe Thunderstorms

The maximum heights of deep convective clouds and overshooting tops have been analyzed and compared using a combination of space and ground-based measurement systems. Deeply convective cumulonimbus clouds are capable of reaching and penetrating the tropopause. The portions of convective clouds that extend into the stratosphere are known as overshooting tops. Instances of tornado onset have been observed to match or slightly lag the timing of maximum cloud-top altitudes. In addition, precise forecasting and measurement of convective cloud-top heights are of critical importance to the safety and efficiency of commercial aviation flight routings. This study included the use of data from three NASA A-Train satellites, 88-D and TDWR Doppler radar, NAM modeling output, and direct visual sightings. The three polar-orbiting satellites included Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, and Aqua. CALIPSO and CloudSat return a vertical profile of microphysical parameters as their near-nadir beams intersect clouds. CALIPSO uses a lidar instrument (CALIOP), operating at 532 and 1064 nm, that is capable of detecting aerosol and small cloud particles. CloudSat uses a radar system called Cloud Profiling Radar (CPR), operating at 94 GHz (3.2 mm), that can penetrate thicker clouds, including those with precipitation. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board Aqua provided a 250m resolution map view that permitted identification of the unique texture of overshooting tops. Satellite data and ground-based Doppler radar were co-located and used to compare cloud-top and echo-top measurements and products. In addition to co-located observational data, North American Mesoscale (NAM) model output with maximum 6-hour lead time was analyzed for convective cloud top forecasts. Finally, direct sightings of cloud tops were made at the time of CALIPSO overpasses of New Jersey. Using a surveyor's transit, the angle from the observation spot to the cloud top was measured and the geographic position of the cloud was determined using MODIS images and Google Earth. After cataloging about 125 A-Train intersects of deep convection from January 1 to July 1 of 2011, the maximum convective cloud altitudes were collected from CALIPSO, CloudSat, radar, and modeling data. Our results confirm previous findings that CALIPSO consistently detects cloud tops at a higher altitude than CloudSat. It was also found that CALIPSO cloud tops were consistently higher than Doppler-radar echo tops or NAM cloud tops. However, CALIPSO altitudes were very consistent with altitudes determined by direct sighting. Doppler radar and modeling data often closely matched satellite observations, but on occasion they showed large differences. Careful analysis of the limitations and the biases of these data could improve our understanding of convective cloud-top dynamics and improve in-flight routing decisions for commercial aviation.