Surface temperature distribution on a spherical ice particle growing by accretion in wet growth regime

Abstract

Experimental evidence has demonstrated that temperature on the surface of an ice particle growing by accretion is not uniform. This non-uniformity is relevant because the ice particle surface temperature is an important microphysical parameter that influences the sign and magnitude of the charge transfer during ice particles collisions. In particular, when high values of ambient temperature and liquid water content are reached, the ice particle surface temperature is expected to reach 0 °C, which is known as wet growth regime. Previous experimental results have shown that wet growth is not uniformly reached on the ice particle surface and a surface temperature distribution is developed. In order to know the surface temperature distribution of a fixed ice particle growing by accretion of supercooled water, numerical calculations were carried out. It was found that the surface temperature distribution has a strong dependence on liquid water content, ambient temperature, airflow velocity and water droplet size. The stagnation point always reaches higher temperatures and, in many cases, its temperature is near 0 °C. For some values of the liquid water content, ambient temperature and airflow velocity, it was possible to determine temperature differences up to 7 °C between the stagnation point and the equator. This variation in the surface temperature implies that the region near the stagnation point would experience wet growth, while the rest of the ice particle surface would remain in dry growth regime, supporting the partial wet growth hypothesis. This could also explain the charge transfer reported during ice particles collisions under wet growth conditions.