Observations of atmospheric waves that moved across northern Alabama on 4 December 2008 using the ARMOR Doppler radar and the Mobile Integrated Profiling System

An atmospheric bore and internal gravity wave were observed on 4 December 2008, using the ARMOR dual-polarimetric Doppler radar and the Mobile Integrated Profiling System, both located in Huntsville, Alabama. These waves occurred as a cold front moved across the Mississippi Valley and into the southeastern United States. The atmospheric bore initiated in the lower Mississippi Valley during the overnight hours and propagated across northern Mississippi and Alabama, away from the front, causing 2 hPa hydraulic jumps in the pressure field. The internal gravity waves were observed in northern Alabama several hours after the bore and as the cold front moved through the region. The environment ahead of the cold front was statically stable (N = 1.6 x 10^-2 s^-1). The speed of the cold front was initially 5 m s^-1 as it moved across northwest Alabama, but it accelerated to 7 m s^-1. The depth of the front as it arrived in Huntsville, AL was only 500-1000 m. Since the cold front was embedded within weak stratiform precipitation, the flows are well represented in the ARMOR data, which was used to conduct a series of RHI scans across the frontal zone while it was within 20 km of the radar. The RHI scans revealed wave-like features propagating atop the cold front. These waves existed in a shear zone between the more statically stable air behind the front and the air forced up and over the front. Thermodynamic and Doppler wind profiles of the cold front indicate these waves are internal gravity waves induced by the shear zone atop the front. A comparison of the wave properties and those of the undular bore as they moved across northern Alabama will be carried out using both in-situ and ground-based remote sensing instruments.