Sun effect on surface hoar illustrated by three case studies

Three case studies demonstrate solar effects on surface hoar crystal size. These effects are presented via: (a) a comparison of night and day time crystal sizes and surface temperatures, (b) a comparison of crystal sizes over different times in one day, and (c) a spatial comparison of tree shadows and surface hoar presence. The three case studies include surface hoar size with overall area sample means from 0.2 mm to 10.3 mm and across the treeline and alpine elevation bands. Although sample locations include various aspects, most of the data are from east aspects. As previous studies have found difficulty explicitly linking physical shortwave and latent heat measurements with surface hoar growth and destruction, this paper takes an empirical approach. Through correlations between temperature and surface hoar size, we find that different processes dominate in alpine versus treeline areas. Also, previous work presents different opinions as to whether summed shortwave or maximum shortwave plays a more important role in surface hoar size change; here, we present data which show the maximum change in incoming direct shortwave affects surface hoar crystal size.

Research highlights► Surface hoar size is affected by maximum increase in direct shortwave input. ► Size change due to shortwave input remains constant independent of crystal size. ► Treeline areas have surface hoar sizes strongly correlated to surface temperature. ► Alpine area has sizes correlated to a delay in surface temperature. ► Findings are applicable with moderate east-facing area shortwave input.