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 atmospheric wave generation. Several tornadic supercells were initiated by such waves in Mississippi, before tracking through north and central Alabama. Additionally, several interactions between waves and preexisting mesocyclones were observed, possibly leading to tornadogenesis. One such interaction occurred within a dual-Doppler analysis domain formed by the Mobile Alabama X-band (MAX) radar and the KHTX WSR-88D, and led to an eventual EF-4 tornado in Jackson Co., AL. Also of particular interest was the development of a wave duct in North Alabama, leading to the generation of ducted gravity waves after 18 UTC. These ducted gravity waves propagated through the UAHuntsville/NSSTC THOR Center and Hazardous Weather Testbed, which includes measurements from the KHTX, the Advanced Radar for Meteorological and Operational Research (ARMOR) C-band radar, the MAX 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 (XPR). 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 expectation of a linear impedance relation between those variables for a gravity wave (Koch and Golus 1988). The ducted gravity waves moved within the ARMOR-KHTX dual-Doppler analysis regions such that complete kinematic analyses could be completed.

The dual-Doppler analyses coupled with the high-resolution MIPS measurements are likely the first complete set of observational analyses on the kinematics of ducted gravity waves and the dynamics of their interactions with convection. This presentation will describe the wave environment over Mississippi and Alabama and also show observations and preliminary analyses of, 1) wave initiated convection, 2) wave-mesocyclone interactions, and 3) ducted gravity waves over North Alabama.