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Airborne Pseudo–Dual Doppler Analysis of a Dryline–Outflow Boundary Intersection

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  • 1 School of Meteorology, University of Oklahoma, Norman, Oklahoma
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Abstract

On 3 June 1995, as part of the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX), the Electra Doppler Radar (ELDORA) onboard the National Center for Atmospheric Research (NCAR) Electra aircraft made possible a high-resolution examination of clear-air motions in the Texas panhandle in and around the intersection of the dryline and a surface baroclinic boundary, a location commonly referred to as the “triple point.” The ELDORA observations, as well as conclusions drawn from analyses of these data, are presented and discussed.

A transverse secondary circulation associated with the dryline is visualized through analyses of the ELDORA data. Typical values of rising and sinking air are found to be 2 m s−1 and 2–3 m s−1, respectively. These vertical velocities are approximately the same as those indicated by in situ data collected onboard the Electra. Because the maximum in rising motion is found at the western edge of the dewpoint gradient and because the low-level relative airflow was from the west, it is suggested that the source region for ascending updraft parcels was primarily from the dry side. The existence of a tilted circulation is also confirmed by dryline-normal cross sections of horizontal divergence, which exhibited a shift of the dryline convergence maximum to the east with height.

Based on vertical cross sections of analyses of ELDORA data just to the north of the triple point, it is shown that there is a residual dryline secondary circulation (RDSC) elevated above the cold pool. Composite hodographs representative of either side of the RDSC identify a distinct difference in the wind profile. The possible roles of the RDSC and outflow boundary to convective initiation are also discussed.

Corresponding author address: Christopher Weiss, University of Oklahoma, 100 E. Boyd, Suite 1310, Norman, OK 73069. Email: cweiss@rossby.metr.ou.edu

Abstract

On 3 June 1995, as part of the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX), the Electra Doppler Radar (ELDORA) onboard the National Center for Atmospheric Research (NCAR) Electra aircraft made possible a high-resolution examination of clear-air motions in the Texas panhandle in and around the intersection of the dryline and a surface baroclinic boundary, a location commonly referred to as the “triple point.” The ELDORA observations, as well as conclusions drawn from analyses of these data, are presented and discussed.

A transverse secondary circulation associated with the dryline is visualized through analyses of the ELDORA data. Typical values of rising and sinking air are found to be 2 m s−1 and 2–3 m s−1, respectively. These vertical velocities are approximately the same as those indicated by in situ data collected onboard the Electra. Because the maximum in rising motion is found at the western edge of the dewpoint gradient and because the low-level relative airflow was from the west, it is suggested that the source region for ascending updraft parcels was primarily from the dry side. The existence of a tilted circulation is also confirmed by dryline-normal cross sections of horizontal divergence, which exhibited a shift of the dryline convergence maximum to the east with height.

Based on vertical cross sections of analyses of ELDORA data just to the north of the triple point, it is shown that there is a residual dryline secondary circulation (RDSC) elevated above the cold pool. Composite hodographs representative of either side of the RDSC identify a distinct difference in the wind profile. The possible roles of the RDSC and outflow boundary to convective initiation are also discussed.

Corresponding author address: Christopher Weiss, University of Oklahoma, 100 E. Boyd, Suite 1310, Norman, OK 73069. Email: cweiss@rossby.metr.ou.edu

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