E.A. Brandes, J. Vivekanandan, J.D. Tuttle, and C.J. Kessinger
Monthly Weather Review, Volume 123 (11), pages 3129-3143.
ABSTRACT
Excellent agreement was found between multiparameter radar signatures of hail, raindrops, and mixed-phase precipitation and in situ precipitation particle measurements made by aircraft in a northeastern Colorado hailstorm. Radar reflectivity estimates determined by remote measurement and from observed particle distributions generally agreed within 5 dB. Maximum values of differential reflectivity (Z_dr) and the fractional contribution of liquid water to total reflectivity (f_rain) differed by less than 0.8 dB and a factor of 2, respectively.
A positive Z_dr column, which extended more than 2 km above the freezing level, was nearly coincident with the storm updraft. The column contained mixed-phase precipitation, but the Z_dr measurement was dominated by a small number of very large raindrops (some exceeding 5 mm in diameter). Trajectories computed with a precipitation growth model suggest that many drops originated with partially or totally melted particles from a quasi-stationary feeder band within the inflow region of the storm. The terminal velocity of the drops composing the Z_dr column exceeded updraft speeds, and therefore, they may have simply fallen from the storm. Although particle observations and radar measurements in the column at approximately 3 km AGL and a temperature of -2 degrees Celsius revealed that the fractional contribution of drops to radar reflectivity was roughly 0.5-0.8, the concentration of supercooled water represented by the drops (a maximum of 0.5 g/m**(-3) and an average of 0.2 g/m**(-3)) was about half that associated with cloud water. Hence, the relative importance of the large drops and consequently that of the Z_dr column as a source of hail embryos, and a factor in hail growth, may have been minor.