Nowcasting thunderstorm anvil clouds over Kennedy Space Center and Cape Canaveral Air Force Station

摘要

Electrified thunderstorm anvil clouds extend the threat of natural and triggered lightning to space launch and landing operations far beyond the immediate vicinity of thunderstorm cells. The deep convective updrafts of thunderstorms transport large amounts of water vapor, supercooled water droplets, and ice crystals into the upper troposphere, forming anvil clouds, which are then carried downstream by the prevailing winds in the anvil-formation layer. Electrified anvil clouds have been observed over the space launch and landing facilities of the John F. Kennedy Space Center and Cape Canaveral Air Force Station (CCAFS), emanating from thunderstorm activity more than 200 km away. Space launch commit criteria and flight rules require launch and landing vehicles to avoid penetration of the nontransparent portion of anvil clouds. The life cycles of 163 anvil clouds over the Florida peninsula and its coastal waters were documented using Geostationary Operational Environmental Satellite (GOES)-8 visible imagery on 49 anvil-case days during the months of May - July 2001. Anvil clouds were found to propagate at the speed and direction of upper-tropospheric winds in the layer from 300 to 150 hPa, approximately 9.4 - 14 km in altitude, with an effective average transport lifetime of approximately 2 h and a standard deviation of approximately 30 min. The effective lifetime refers to the time required for the nontransparent leading edge of an anvil cloud to reach its maximum extent before beginning to dissipate. The information about propagation and lifetime was incorporated into the design, construction, and implementation of an objective short-range anvil forecast tool based on upper-air observations, for use on the Meteorological Interactive Data Display System within the Range Weather Operations facility of the 45th Weather Squadron at CCAFS and the Spaceflight Meteorology Group at Johnson Space Center.