Waterspout Velocity Measurements by Airborne Doppler Lidar

R. L. Schwiesow National Oceanic and Atmospheric Administration, Wave Propagation Laboratory, Boulder, Colorado 80303

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R. E. Cupp National Oceanic and Atmospheric Administration, Wave Propagation Laboratory, Boulder, Colorado 80303

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P. C. Sinclair Colorado State University, Atmospheric Science Department, Ft. Collins 80521

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R. F. Abbey Jr. U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, Washington, D.C. 20555

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Abstract

A Doppler lidar measures the line-of-sight velocity of cloud droplets in a waterspout much as a meteorological Doppler radar measures the velocity of larger hydrometeors. We discuss details of the application of an airborne Doppler lidar to waterspout velocity measurements, including intensity weighting and limitations of the technique. One type of result available from the lidar data is the velocity spectrum of the line-of-sight velocity component of scatterers in the flow, integrated along the lidar axis, as a function of distance from the vortex axis. From the velocity spectra, peak winds in the portion of the waterspout marked by cloud droplets, turbulence levels, and interaction with the ambient flow can be inferred. In one example the maximum velocity observed in the visible part of the waterspout is 10 m s−1. This double-walled waterspout showed a two-peaked velocity spectrum, which we interpret as a dynamic difference between the two coaxial components of the vortex.

Abstract

A Doppler lidar measures the line-of-sight velocity of cloud droplets in a waterspout much as a meteorological Doppler radar measures the velocity of larger hydrometeors. We discuss details of the application of an airborne Doppler lidar to waterspout velocity measurements, including intensity weighting and limitations of the technique. One type of result available from the lidar data is the velocity spectrum of the line-of-sight velocity component of scatterers in the flow, integrated along the lidar axis, as a function of distance from the vortex axis. From the velocity spectra, peak winds in the portion of the waterspout marked by cloud droplets, turbulence levels, and interaction with the ambient flow can be inferred. In one example the maximum velocity observed in the visible part of the waterspout is 10 m s−1. This double-walled waterspout showed a two-peaked velocity spectrum, which we interpret as a dynamic difference between the two coaxial components of the vortex.

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