THERMAL-CONDUCTIVITY OF POROUS ICE IN HAILSTONE SHELLS

The thermal conductivity and diffusivity of porous ice accreted on sph erical and spheroidal hailstone models were measured over a density ra nge of 620-915 kg m(-3). By scanning the evolving surface temperature distributions during cooling in a cold airflow the thermal conductivit y was varied in iterative fashion until the internal heat flux produce d the correct surface temperature distribution. The results indicate a linear dependence of the thermal conductivity, k(i), and diffusivity, alpha(i), on density. For example, lowering the density by 10% lowers k(i) by 15%. Within the range of cloud conditions; the density variat ions affect the thermal parameters more than temperature does. The res ults also indicate a continuous decrease of the thermal conductivity f rom bulk ice via consolidated porous ice to loosely packed snow.