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Criteria for the Detection of Hail Cells

A. WaldvogelAtmospheric Physics, ETH, 8093 Zürich, Switzerland

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B. FedererAtmospheric Physics, ETH, 8093 Zürich, Switzerland

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P. GrimmAtmospheric Physics, ETH, 8093 Zürich, Switzerland

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Abstract

One of the Soviet seeding criteria used to detect hail cells at an early stage of development is examined. The radar history of 195 strong convective cells is studied and compared with information of a dense hailpad network (323 pads per 1292 km2). It is found that all hail-bearing cells are detected early in their development. About 50% of the 71 cells which met the seeding criterion never produced hail on the ground. This corresponds to a 30% waste of seeding rockets. The criterion which uses six radar parameters can be replaced by a simpler and slightly more efficient criterion which necessitates only the determination of the height of the 45 dBZ contour H45 in relation to the melting level H0. The new criterion is compared with other criteria and its microphysical implications are discussed.

Abstract

One of the Soviet seeding criteria used to detect hail cells at an early stage of development is examined. The radar history of 195 strong convective cells is studied and compared with information of a dense hailpad network (323 pads per 1292 km2). It is found that all hail-bearing cells are detected early in their development. About 50% of the 71 cells which met the seeding criterion never produced hail on the ground. This corresponds to a 30% waste of seeding rockets. The criterion which uses six radar parameters can be replaced by a simpler and slightly more efficient criterion which necessitates only the determination of the height of the 45 dBZ contour H45 in relation to the melting level H0. The new criterion is compared with other criteria and its microphysical implications are discussed.

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