A STUDY OF THUNDERSTORM MICROPHYSICS WITH MULTIPARAMETER RADAR AND AIRCRAFT OBSERVATIONS

Excellent agreement was found between multiparameter radar signatures of hail, raindrops, and mixed-phase precipitation and in situ precipit ation particle measurements made by aircraft in a northeastern Colorad o hailstorm. Radar reflectivity estimates determined by remote measure ment and from observed particle distributions generally agreed within 5 dB. Maximum values of differential reflectivity (Z(DR)) and the frac tional contribution of liquid water to total reflectivity (f(rain)) di ffered 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 mi xed-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 exceede d updraft speeds, and therefore, they may have simply fallen from the storm. Although particle observations and radar measurements in the co lumn at approximately 3 km AGL and a temperature of -2 degrees C revea led that the fractional contribution of drops to radar reflectivity wa s 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 i mportance 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 be en minor.