Observations of the Finescale Structure of a Dryline during VORTEX 95

Abstract

The three-dimensional finescale structure of a dryline observed over the Texas panhandle during the Verification of the Origins in Tornadoes Experiment (VORTEX) on 6 May 1995 is presented. High-resolution observations documenting dryline evolution were collected from midafternoon while it moved slowly eastward until late afternoon as it retrogressed back to the west. Dryline variability in the horizontal along-line direction was revealed by airborne Doppler radar observations from the National Center for Atmospheric Research Electra Doppler radar and ground-based measurements from the nearby WSR-88D at Amarillo, Texas. This variability was created as the dryline interacted with horizontal convective rolls forming west of the dryline. The rolls intersected the dryline at periodic locations creating radar reflectivity and vertical velocity maxima. More importantly, clouds initiated at these intersection points. Additional dryline variability was generated through the interaction of the low-level flow with the local topography. The kinematic and thermodynamic characteristics of the leading edge of the dryline circulation closely resembles those of laboratory and atmospheric density currents such as the sea breeze. A comparison between the observed and calculated dryline propagation speeds suggests that the flow?force balance between the cross-frontal acceleration and the density gradient, which exists for density currents, occurs only on the horizontal scale of the leading edge (2?5 km) of the dryline circulation.