Hailstones, the main source of the cold rain process

Robust new heat and mass transfer equations, accommodating measured effects of drag, turbulence and gyration, address the growth of hailstones within a diameter range of 0.5 to 8 cm They also form the basis of the new findings on the importance of shedding of rain drops. Hailstone growth is governed by seven variables. A new classification into three types, applied to a Denver hail cloud environment, is presented. Together with case-specific heat and mass transfers a reduction to three variables is possible. Two of those, however, are new variables based on pairs of four “old” ones. Finally, the understanding that spherical hailstones grow while gyrating, allows the conclusion that homogeneous radial growth produces homogeneous surface temperatures. This is a consequence of all surface points being equally exposed to accretion. Evidence is produced showing that nearly all in-cloud growth conditions lead to spongy hailstones that shed rain sized drops. [A gyration is composed of a nutation and a precession of the spin axis that moves about the horizontal gyration axis at an angle of 45o, the intersection at the center of the hailstone.] Gyration and spin rates exceeding 15 Hz are further enhancing shedding. Shed rain drop-sized particles continuously initiate and feed a warm rain process that is parallel to the hail process. [Melting of hailstones adds to the rain, but does not control it.] Observations that the ice phase is required to produce decent rain in Malaysia and Indonesia, strongly points to the existence of substantial shedding – even in the tropics.