OBSERVATIONS OF LOW-LEVEL BAROCLINITY GENERATED BY ANVIL SHADOWS

Low-level cooling beneath the cirrus anvil canopies of supercell thund erstorms is documented in two Verification of the Origins of Rotation in Tornadoes Experiment cases and in the 17 May 1981 Arcadia, Oklahoma , supercell. Surface temperature decreases of 3 degrees C or more occu rred beneath the anvils within 45 min of the onset of overcast conditi ons. Cooling was confined to the lowest few hundred meters of the boun dary layer, and believed to be due mainly to a deficit in the energy b udget following a reduction of incoming shortwave radiation. In the th ree cases studied, the vertical wind shear was strong; thus, mixing pr evented the formation of an inversion layer Strong insolation at the g round outside of the anvil shadows coupled with the cooling beneath th e cirrus canopies led to corridors of baroclinity along the shadow edg es. It is shown that residence times in these baroclinic zones may be long enough for parcels to acquire considerable horizontal vorticity ( e.g., similar to 10(-2) s(-1)) cn route to a storm updraft. Enhancemen t of the horizontal vorticity of parcels ingested by an updraft may ha ve implications for the dynamics of storm rotation.