Extended Abstract (5.0M)5A.8
Centrifuging of scatterers in tornadoes
David C. Dowell, NOAA/NCAR, Boulder, CO; and J. Wurman and L. J. Wicker
Fine resolution radar observations typically indicate a region of low reflectivity surrounded by a ring of high reflectivity in a tornado. This reflectivity distribution presumably results from centrifuging of scatterers away from the core of the vortex.
The radar scatterers surrounding tornado weak-echo holes are likely debris, rain, and/or hail. We employ a simple axisymmetric numerical model to simulate the distribution of scatterers of varying types in a vortex. We will compare the simulations to several cases of the formation of weak-echo holes in tornadoes that have been captured at close range with the Doppler on Wheels.
Since the radar measures scatterer motion, rather than air motion, attempts to synthesize the wind field in a tornado from Doppler radar measurements are biased by the motion of the scatterers away from the vortex center. The magnitude of the bias in horizontal divergence estimates depends on both the characteristics of the velocity profile and the nature of the scatterers.
Session 5A, Severe Weather—Supercells & Tornadoes (Parallel with Session 5B)
Friday, 20 July 2001, 4:00 PM-6:00 PM
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