Sunday, 22 January 2012
Investigating Diurnal Variations of Tornadic Environments in the Southeast United States
Hall E (New Orleans Convention Center )
Although previous studies have determined that the nocturnal low-level jet enhances nighttime tornadogenesis by adding moisture and shear to the pre-tornadic environment (e.g., Kis and Straka 2010), the behavior and genesis mechanisms of severe nighttime tornado environments are otherwise not well understood. Other studies have focused primarily on the pre-tornadic nighttime environments in the Great Plains and eastern two-thirds of the United States, but this phenomenon has not been examined extensively in the Southeast United States (the location of “Dixie Alley”). Since 42% of tornado fatalities occur at night, and the majority of those happen outside “Tornado Alley” (Ashley 2008), nocturnal tornadoes in the Southeast warrant further analysis. This study investigates diurnal variations of tornadic environments in the Southeast using CFS reanalysis data to represent EF-1 or greater daytime and nighttime tornado events from 1979 to 2009. Tornado events are separated into daytime and nighttime occurrences using the top of the atmosphere downward shortwave radiation flux parameter from reanalysis. Statistical tests show that both dynamic and thermodynamic variables are significantly different for daytime and nighttime tornadoes.