This visualization is based on the first three-dimensional numerical model of melting snowflakes in the atmosphere, developed by scientist Jussi Leinonen of NASA's Jet Propulsion Laboratory in Pasadena, California. A better understanding of how snow melts can help scientists recognize the signature in radar signals of heavier, wetter snow -- the kind that breaks power lines and tree limbs -- and could be a step toward improving predictions of this hazard.
The model reproduces key features of melting snowflakes that have been observed in nature: first, meltwater gathers in any concave regions of the snowflake's surface. These liquid-water regions merge as they grow and eventually form a shell of liquid around an ice core, finally developing into a water drop.
The visualization shows a typical snowflake less than half an inch (one centimeter) long. The snowflake is composed of individual ice crystals whose arms became entangled when they collided in the air. The extremities of the arms melt first because they are more exposed to heat from the surrounding air. Water first fills small cavities within the ice crystals, and then these overflow, allowing water to pool into droplets.
"I got interested in modeling melting snow because of the way it affects our observations with remote sensing instruments," Leinonen said. A radar "profile" of the atmosphere from top to bottom shows a very bright, prominent layer at the altitude where falling snow and hail melt, much brighter than the layers above and below. "The reasons for this layer are still not particularly clear, and there has been a bit of debate in the community," Leinonen explained.
Simpler models can reproduce the bright melt layer, but a more detailed model like this one can help scientists to understand it better, particularly how the type of melting snow and the radar wavelengths used to observe it relate to the brightness of the layer.
A paper on the numerical model, titled "Snowflake melting simulation using smoothed particle hydrodynamics," recently appeared in the Journal of Geophysical Research - Atmospheres.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 18.104.22.168.0