SEET

The main goal of the Study of Electrical Evolution in Thunderstorms was to measure the evolution of principal charge regions inside small thunderstorms that occurred over central New Mexico.

In order to meet his needs, SSSF modified their GPS dropsondes to be used in a balloon-borne, "up-sonde" mode of operation, tracking four sondes simultaneously to permit multiple, simultaneous, electric field soundings. Three to six sondes were launched into each thunderstorm with individual launches separated by 5 to 10 minutes. Each balloon carried an electric field meter to provide electric field data and the dropsonde to provide position data and thermodynamic sounding throughout the cloud. To meet positioning requirement, an OEM code-correlating GPS receiver was replaced by the standard codeless GPS receivers, i.e., full GPS position calculations happened with in the sonde itself rather than in the ground- or air-based receiver system. An air flow scoop was also added to the sonde for ventilation of the temperature and relative humidity sensors.

A total of 30 soundings were made and the "upsonde GPS dropsondes" performance was excellence not just meeting but exceeding data and accuracy requirements as well as quality control aspects of data compilation. For the first time precise locations of charge regions inside thunderstorms were measured and the scientific data exceeded all other thunderstorm electric field measurements collected so far.

The lead engineers for the development of the GPS dropsondes are Terry Hock and Dean Lauritsen of NCAR/EOL.