An international team of scientists has developed a numerical 3D model for the melting of single snowflakes. A better understanding of how snow melts can help researchers recognize the signature in radar signals of heavier, wetter snow and could be a step toward improving predictions of this hazard.
The team’s 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. Image credit: Free-Photos.
“Rain often starts as snow higher in the atmosphere, where it is colder. The snowflakes melt as they fall into above-freezing temperatures. The layer of melting snowflakes can, among other things, affect weather patterns, block radio signals, and be a hazard to aircraft,” said study authors Dr. Jussi Leinonen of NASA’s Jet Propulsion Laboratory and Annakaisa von Lerber of Aalto University and Finnish Meteorological Institute.
“Our study was the first to simulate the melting of snowflakes in 3D by reproducing the physical processes involved on a computer.”
The team’s numerical 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 then merge to form a shell of liquid around an ice core, and finally develop into a water drop.
The modeled snowflake shown in the video is less than half an inch (1 cm) long and composed of many individual ice crystals whose arms became entangled when they collided in midair.
“I got interested in modeling melting snow because of the way it affects our observations with remote sensing instruments,” Dr. 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 atmospheric layers above and below it.”
“The reasons for this layer are still not particularly clear, and there has been a bit of debate in the community,” he said.
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 layer is related to both the type of melting snow and the radar wavelengths used to observe it.
A paper on the team’s numerical model was published in the Journal of Geophysical Research – Atmospheres.
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Jussi Leinonen & Annakaisa von Lerber. Snowflake Melting Simulation Using Smoothed Particle Hydrodynamics. Journal of Geophysical Research – Atmospheres, published online February 6, 2018; doi: 10.1002/2017JD027909
