Determining the characteristics of anvil and thunderstorm lightning for use in the Lightning Launch Commit Criteria at Cape Canaveral Air Force Station and Kennedy Space Center.

摘要

The 45th Weather Squadron (45WS) provides weather support to America's space program at Florida's Cape Canaveral Air Force Station (CCAFS), Kennedy Space Center (KSC), and Patrick Air Force Base (PAFB). Since CCAFS/KSC lies within Florida's "Lightning Alley", summer thunderstorms and associated hazards are a special concern for space launches and all other outdoor activities at CCAFS/KSC. Therefore, the 45WS has developed the Lightning Launch Commit Criteria (LLCC) to help minimize hazards from lightning (both naturally occurring and triggered) and vehicle electrification during the ascent phase of launch.;This study has documented the spatial distributions and time evolution of total lightning and radar reflectivity in and around thunderstorms, attached anvil clouds, and detached anvil clouds near CCAFS/KSC on 30 active lightning days between 2008-11. Our goal was to determine if some of the current LLCC thresholds are too restrictive and represent missed launch opportunities, or not restrictive enough and represent a safety risk. CG flashes originating inside the convective core or its anvil can strike the ground away from the cloud edge. Since these side flashes often strike the ground under clear skies, they commonly are referred to as "bolts from the blue". Our results indicate that the vast majority of CG flashes (∼94%) strike the ground ≤ 5 n mi from cloud edge (0 dBZ) whereas 73% of CG flashes are ≤ 3 n mi outside 0 dBZ. Three positive bolts from the blue were documented, and all came from the same storm on 29 May 2009. One of the positive flashes propagated 8.91 n mi from cloud edge. Anvil initiated lightning can distribute charge after detachment, but only for a short period.;We analyzed 100 anvils within 100 km of KSC; 895 IC flashes in the anvil were initiated in the core of the storms. The first core initiated flash of each anvil typically propagated = 10 n mi. Cellular thunderstorms produce the greatest percentage of total lightning (∼84%) in our dataset, but average flash distances from the core are greatest in attached anvils (∼4.98 n mi).;To our knowledge this is the first study to quantify the distances that lightning can extend beyond the edge of clouds. We believe the results of this research should be considered before making additional changes to the LLCC.