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Microburst Rotation: Simulations and Observations

Ronald E. RinehartDepartment of Atmospheric Sciences, University of North Dakota, Grand Forks, North Dakota

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Alan BorhoDepartment of Atmospheric Sciences, University of North Dakota, Grand Forks, North Dakota

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Charles CurtissDepartment of Atmospheric Sciences, University of North Dakota, Grand Forks, North Dakota

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Abstract

Microburst rotation can be determined by measuring the difference in azimuths between the maximum approaching and maximum receding velocity centers on a Doppler radar. Nonrotating microbursts would have these centers exactly along the same radial from the radar. Microbursts rotating clockwise would have the approaching center clockwise of the receding center, and vise versa. In the fist part of this study the authors develop the relationships between the uniform wind, source strength, and rotational strength using potential flow theory and apply this to simulating real microbursts. In the second part the authors give observations of microburst rotation based on measurements of 908 microbursts made near Orlando, Florida, during 1992. While most microbursts had little rotation, 55.4% rotated cyclonically. The average tangential velocity of the rotational component was 1.1 m s−1; 5% had rotations equal to or greater than 2.5 m s−1. This may have significant implications for aviation. Finally, microburst strength measurements are compared with velocity shear and F factors for the 908 microbursts.

Abstract

Microburst rotation can be determined by measuring the difference in azimuths between the maximum approaching and maximum receding velocity centers on a Doppler radar. Nonrotating microbursts would have these centers exactly along the same radial from the radar. Microbursts rotating clockwise would have the approaching center clockwise of the receding center, and vise versa. In the fist part of this study the authors develop the relationships between the uniform wind, source strength, and rotational strength using potential flow theory and apply this to simulating real microbursts. In the second part the authors give observations of microburst rotation based on measurements of 908 microbursts made near Orlando, Florida, during 1992. While most microbursts had little rotation, 55.4% rotated cyclonically. The average tangential velocity of the rotational component was 1.1 m s−1; 5% had rotations equal to or greater than 2.5 m s−1. This may have significant implications for aviation. Finally, microburst strength measurements are compared with velocity shear and F factors for the 908 microbursts.

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