Why the speed snowflakes fall matters for climate change

By James Gamble via SWNS

How fast snowflakes fall can have important implications for the speed of climate change, according to new research.

Scientists studying how snowflakes swirl towards the ground found they all fall in the same pattern - regardless of their type or turbulence in the atmosphere.

But they now believe that tracking the slight differences in how fast they fall can have an important impact on how fast we can expect the climate to warm.

The American research team added that tracking snowflakes using lasers could also help them in forecasting the durations of storms.

Snowflakes - single ice crystals that have achieved sufficient size and fall through the Earth's atmosphere as snow - swirl and dance their way to the ground instead of plummeting, and their path can have implications far beyond the interests of skiers and children hoping for a snow day.

Researchers from the University of Utah say determining snowflake fall speed can also be crucial for predicting weather patterns and measuring climate change.

In a study published in the journal Physics of Fluids, the researchers investigated snowflake accelerations in atmospheric turbulence.

They found that, regardless of turbulence or snowflake type, acceleration follows a universal statistical pattern that can be described as an 'exponential distribution'.

Professor Timothy Garrett, one of the lead authors of the study, explained: "Even in the tropics, precipitation often starts its lifetime as snow.

“How fast precipitation falls greatly affects storm lifetimes and trajectories and the extent of cloud cover that may amplify or diminish climate change.

"Just small tweaks in model representations of snowflake fall speed can have important impacts on both storm forecasting and how fast climate can be expected to warm for a given level of elevated greenhouse gas concentrations."

The researchers set up in a ski area near Salt Lake City in Utah, where they battled an unprecedented 900 inches of snow.

They filmed snowfall and measured atmospheric turbulence, using a self-invented device that employs a laser light sheet to gather information about snowflake mass, size, and density.

"Generally, as expected, we find that low-density ‘fluffy’ snowflakes are most responsive to surrounding turbulent eddies,” Dr. Garrett said.

However, the researchers found snowflake accelerations follow an exponential frequency distribution with an exponent of three halves.

In analyzing their data, they also discovered that changes in the terminal velocity frequency distribution followed the same pattern.

“Snowflakes are complicated, and turbulence is irregular," Dr. Garrett said.

"The simplicity of the problem is actually quite mysterious, particularly given there is this correspondence between the variability of terminal velocities – something ostensibly independent of turbulence – and accelerations of the snowflakes as they are locally buffeted by turbulence."

Because size determines terminal velocity, a possible explanation for the team's findings is that the turbulence in clouds that influences snowflake size is related to the turbulence measured at the ground - though the factor of three halves remains a mystery.

Dr. Garrett's team will revisit their experiment this winter, using a mist of oil droplets to obtain a closer look at turbulence and its impact on snowflakes.