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John W. Conway
and
Dušan S. Zrnić

Abstract

The origin and importance to embryo and hail production of a region of drops advected above the freezing level in the updraft of a severe Colorado hailstorm is examined using radar polarization measurements in conjunction with dual-Doppler and trajectory analysis. These drops, which give a distinct radar signature termed the “differential reflectivity column,” originate from 1) melted hydrometeors that fall from the back-sheared anvil, through the embryo curtain, and are recirculated into the storm updraft, and 2) in situ drop growth within the updraft. Some of the drops refreeze and likely produce frozen-drop hailstone embryos.

Numerous hailstone trajectories are found to cross either through, or over, the drop column where the hailstones undergo a significant growth phase. Two separate hailstone fallout regions are identified. Some hailstones in the northern fallout region show anticyclonic trajectories and in situ updraft and column growth. Others grow while crossing the top of the vault. Hailstones in the southern region exhibit growth while passing cyclonically through the column or over the vault.

A new method to determine hydrometeor fall speeds from radar polarization measurements for use with dual-Doppler analysis is introduced.

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