资源环境科技发展态势分析平台

This study documents an environment for which small changes therein significantly impacted electrification and for which current theories of electrification lacked the ability to discriminate storm polarity. Thirty single-cell and multicell storms from 1900 to 2200 UTC on 4 June 2012 over a 150- by 100-km West Texas region were examined. Some of these storms had anomalous charge structures (primarily positive charge in the midlevels at -10 degrees C to -30 degrees C or 6.3 to 8.8km above MSL locally) and some normal (primarily negative at midlevels), even though they existed concurrently and did not statistically differ in overall flash sizes, flash rates, radar volume, or echo top height. Overall, the normal storms ingested lower equivalent potential temperature surface air and were estimated to experience lower convective available potential energy than the anomalous storms, as observed in other studies. They were, however, estimated to have smaller warm cloud depth and surface dew point temperatures, contrary to expectations. Significant overlap between the storm environments suggested that lower instability may have contributed to some storms becoming normally electrified, but it was not a sufficient condition. Additionally, there had been previous convection in the region dominated by normal-polarity storms. A Weather Research and Forecasting ensemble suggested that the previous convection moistened the midlevels of the atmosphere near cloud base. We propose that future studies investigate dry-air entrainment as an additional, intertwined environmental factor that could decrease droplet sizes and effective warm rain processes, promoting positive graupel charging in the midlevels and anomalous charge structures.