NASA Visualizes the Dance of a Melting Snowflake

A new video features a visualization of the first three-dimensional numerical model of melting snowflakes in the atmosphere, developed by scientist Jussi Leinonen.
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.

Snowflake research is one of many ways that NASA studies the frozen regions of Earth, collectively known as the cryosphere.

Leinonen’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 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 (one centimeter) long and composed of many individual ice crystals whose arms became entangled when they collided in midair.

Leinonen said he became interested in modeling melting snow because of the way it affects observations with remote sensing instruments. 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,” Leinonen said.

Simpler models can reproduce the bright melt layer, but a more detailed model like this one can help scientists understand it better, particularly how the layer is related to the type of melting snow and the radar wavelengths used to observe it.

A paper on the numerical model, titled “Snowflake melting simulation using smoothed particle hydrodynamics,” recently appeared in the Journal of Geophysical Research -Atmospheres.