New Hailstone Physics. Part II: Interaction of the Variables

Abstract

Abstract The reduction of parameter dimensions in Part I is complemented by the compaction of parameter space in Part II. The range of diameters is 0.5 ≤ D ≤ 8 cm, and the assumed liquid water content varies within 1 ≤ Wf ≤ 3 for dry growth and Wf ≤ 6 g m−3 for shedding. Entirely new data throw new light onto HMT and growth. Results are as follows: (i) dry growth is unimportant, since most hailstones grow spongy; (ii) radial growth is slow for dry and fast for spongy growth because less latent heat of freezing needs to be discarded if a smaller portion of the accreted water is frozen: this growth with shedding is particularly effective if the product Y of the net collection efficiency and ice mass fraction of the deposit is 0.2 ≤ Y ≤ 0.6; (iii) the lowest possible surface temperature tS for dry growth is −32.3°C. For water-skin-covered, spongy particles tS > −5°C, and tS > −0.55°C for shedding from wet surfaces without water skins; and (iv) the interplay between water-skin thickness and surface temperature allows interconnection of all variables. However, new icing experiments are necessary to prove the proposed sphere growth by special gyration, to quantify the components of Y, and to address water-skin properties and growth. Radically redesigned dynamic cloud models need to incorporate hail packaging and rain spectra evolution in clouds. The latter will connect hailstone shedding with a warm rain process that is parallel to and interacts with hail formation.