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A Method for Estimating Particle Fall Velocities from Vertically Pointing Doppler Radar

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  • 1 NOAA/ERL/Environmental Technology Laboratory, Boulder, Colorado
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Abstract

A method is presented that estimates particle fall velocities from Doppler velocity and reflectivity measurements taken with a vertically pointing Doppler radar. The method is applicable to uniform, stratified clouds and is applied here to cirrus clouds. A unique aspect of the technique consists of partitioning the Doppler velocities into discrete cloud height and cloud reflectivity bins prior to temporal averaging. The first step of the method is to temporally average the partitioned Doppler velocities over an hour or two to remove the effects of small-scale vertical air motions. This establishes relationships between particle fall velocity and radar reflectivity at various levels within the cloud. Comparisons with aircraft in situ observations from other experiments show consistency with the remote-sensing observations. These results suggest that particle fall speeds can be determined to within 5–10 cm s−1 by means of this technique.

Corresponding author address: Brad W. Orr, NOAA/ERL/ETL, 325 Broadway, Boulder, CO 80303.

Email: borr@etl.noaa.gov

Abstract

A method is presented that estimates particle fall velocities from Doppler velocity and reflectivity measurements taken with a vertically pointing Doppler radar. The method is applicable to uniform, stratified clouds and is applied here to cirrus clouds. A unique aspect of the technique consists of partitioning the Doppler velocities into discrete cloud height and cloud reflectivity bins prior to temporal averaging. The first step of the method is to temporally average the partitioned Doppler velocities over an hour or two to remove the effects of small-scale vertical air motions. This establishes relationships between particle fall velocity and radar reflectivity at various levels within the cloud. Comparisons with aircraft in situ observations from other experiments show consistency with the remote-sensing observations. These results suggest that particle fall speeds can be determined to within 5–10 cm s−1 by means of this technique.

Corresponding author address: Brad W. Orr, NOAA/ERL/ETL, 325 Broadway, Boulder, CO 80303.

Email: borr@etl.noaa.gov

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