Surface temperature variations of gyrating hailstones and effects of pressure-temperature coupling on growth

Simultaneous measurements of surface temperatures in the equatorial and polar regions of gyrating hailstones, growing in a closed circuit wind tunnel, were performed using two infrared microscopes. Results indicate that a temperature difference as high as 5.9°C existed between these regions, with maximum differences occurring in the liquid water content range of 1.5 to 6.4 g m−3. Under such conditions growth was generally characterized by a dry, cold regime at the poles and a wet, warmer regime at the equator. Thus, contrary to standard assumptions, the surface temperature of growing hailstones cannot be considered homogeneous. arison of the hailstone growth results from the present study, performed at laboratory pressure, with those of García-García and List (1992), who varied air pressure with temperature according to the Denver soundings (Beckwith, 1960), indicates that the mass growth rate is enhanced at lower pressures due to the combination of increased terminal velocity and collection efficiency. Smaller ice fractions in deposits were measured at lower air pressures for comparable air temperatures and liquid water contents. This investigation demonstrates the difficulty of extrapolating from laboratory pressure to hail growth regions at lower pressure. An examination of the governing equations shows that such a simulation is physically impossible.