Observations and Analysis of Atmospheric Waves during the Historic April 27, 2011 Tornado Outbreak

The environment that led to the historic 27 April 2011 tornado outbreak in the Southeast was one also conducive to the generation of shear based atmospheric waves. Several interactions between waves or wave packets and preexisting mesocyclones were observed, similar to those described by Coleman and Knupp (2008). One interaction occurred within a dual-Doppler (DD) analysis domain formed by UAHuntsville's Mobile Alabama X-band (MAX) polarimetric radar, which was deployed 34 km west of the WSR-88D radar located in Hytop, AL (KHTX). The interaction preceded development of an EF-4 tornado in Jackson Co., AL, within the DD domain. This case affords the opportunity to study the dynamics of the wave interaction and determine what (if any) role it played in tornadogenesis.

Also of particular interest was the development and propagation of ducted gravity waves after 1800 UTC in north Alabama. These ducted waves propagated through the heart of the UAHuntsville/NSSTC THOR Center and Hazardous Weather Testbed, which includes measurements from KHTX, MAX, the Advanced Radar for Meteorological and Operational Research (ARMOR) C-band polarimetric radar, as well as the instrument suite on board the Mobile Integrated Profiling System (MIPS), including high temporal measurements (6 Hz) by a vertically pointing X-band profiling radar. As the waves moved over the MIPS site, they were associated with correlated surface pressure and wind speed perturbations of > 1 mb and 5 m/s, respectively, which matches expectations of a linear impedance relation for a gravity wave (Koch and Golus 1988). The ducted gravity waves moved within the ARMOR–KHTX DD analysis domain such that complete kinematic analyses could be completed. This multi-sensor approach is likely the first complete set of observational analyses on the kinematics of ducted gravity waves within a tornadic environemnt.