A preliminary investigation of an atmospheric bore and a waves atop a cold front that moved across northern Alabama on 4 December 2008 Patrick Gatlin ATS 651 Class Project Spring 2009

NEXRAD Mosaic 03,06,07 UTC

Mesoscale Analysis Dashed line represents cold front position

NSSTC Observations Outflow boundary from cold front convection triggers an atmospheric bore Bore passes through NSSTC at 0800 UTC  2.5 mb pressure rise in 10-min  BL deepens Hydraulic jump

ARMOR image of bore Bore already past radar at 0800 UTC Large variations in wind field behind bore

Surface Observations cold fropa Hydraulic jump Bore speed ~ 14 m s -1

ARMOR images of cold front RSA sounding shows very shallow duct (D ~ 500 m)  conducive to wave propagation Well delineated fine line in radar data (convergence ~ 0.06 s -1 ) Radial velocity was all outbound at 2deg elevation  very shallow airmass behind cold front Redstone 1200 UTC Duct 0.7 deg 2.0 deg

ARMOR reflectivity RHI scans perpendicular to cold front 2 distinct airmasses are shown by the reflectivity field Denser airmass is ~ 1.5 km deep Flow up and over the denser airmass can be seen in the radial velocity field Watch as waves propagate along the interface of the airmasses λ ~ 1.2 km