The Direct Measurement of the Sizes, Shapes and Kinematics of Falling Hailstones

Abstract The kinematic behavior of hailstones falling in their natural environment near the surface was studied using stroboscopic photography in a mobile van. The experimental results permitted determination of the shape and dimensions, velocity, and in a few cases the rotation rate, of hailstones failing into the van. Hailstones were sampled in southeast Wyoming, southwest Nebraska and northeast Colorado. About 84% of the hailstones photographed were classified spheroidal, the remainder being roughly conical. Change in orientation of stones is observed in most photographs, though only ∼6% of the hailstones could be assigned a rotation rate. Velocity data were obtained for more than 600 hailstones in the diameter range 5-25 mm. It is shown that the vertical velocity component of hailstones near the surface (air density =9.93×10−4 g cm−3) can be predicted by the expression VT where De0.50 (±m s−1), Deis the equivalent volume diameter of a spherical hailstone in centimeters. Fall-speed and hailstone oblate...