Utah's Mountains Vasatch are famous for having "the biggest snow on earth". Snow seekers looking for skiing and world-class snowboarding contribute to the economy over a billion dollars a year. Snovmelt also supplies most of the fast-growing populations along the Vasatt Front, including Salt Lake City. Understanding what controls the timing and size of snow melting is critical to Yut.
It's more complicated than warming air temperature; Solar energy and longer light in the spring are the main drivers of snow melting. As you wear a black shirt on a hot day, everything that darkens the surface of the snow – such as dust – will absorb more sunlight and accelerate melting. As people continue to change landscapes, dust will probably hit nearby peaks. However, scientists are just beginning to understand the impact of dust on the snow.
A new study by the University of Utah has analyzed the effects of dust deposition on mountain studying land in Alta, Utah in the Vasatt Mountains. For the first time, researchers measured dust in the air and snow at the same time. They found that one storm of dust on April 13, 2017 deposited half of the dust for the season. The additional sunlight absorbed by the dust darkened the snow surface and a week earlier it led to the melting of snow.
Using computer simulations, the team modeled where the dust came from. They found that first, before the storm, the dust came from the south, but then moved to the west. The Western winds brought dust from "hot spots" in the dry summit of the Great Salt Lake, a relatively new source of dust due to the historically low levels of the lake.
"What is important for the Great Salt Lake is that there are no water rights, nor a policy to maintain the level of the lake. As the lake is diminishing, it is predicted that dust events will become more frequent, "says McKenzie Skiles, assistant professor of geography at U and the lead author of the study. "Anything that affects the melting of snow could have economic and hydrological consequences. And now it's one of the regions with dust sources in the immediate vicinity. Could we do something about this issue by adopting a policy that maintains the minimum level of the lake? "
Study published online December 21st in the journal Environmental Research Letters.
Sinking snow in Vasatch
Skiles and her team watched five dust events in the spring of 2017, but focused on a storm on April 13, as it deposited the largest amount of dust, and because it seemed that dust came from a dry lake of the Great Salt Lake. The team collected data from the Atvater studio, near the Alta ski resort in Alta, Utah. They collected data in three ways. First, they sampled the size and number of particles transmitted by air. Second, the caves were dug to analyze the properties of snow and the concentration of dust samples. Thirdly, they used computer simulations to evaluate where the dust came from and where it would be expected to go. They were confident in simulations as they captured samples in samples from the air and snow.
To measure how the dust was affecting the snow, Skiles calculated the difference in energy absorption between the snow that was darkened by dust and the same snow if it was dust free. The equation includes snow features such as snow size, snow depth, depth and aerosol mixing. The total impact of dust is a melting acceleration of 25%.
They found that most of the dust was deposited about an hour after the real storm had passed, in the so-called "post-frontal" winds. Sources such as the Great Salt Lake Desert were the biggest dust emitters; dust from the dry lakes of the lake made up about 10% of the deposited dust. However, computer simulations suggest that much of the dust has exploded north of the study pit. Without observing snow in the region, the researchers were unable to confirm more dust deposition, but assumed that the effect was probably higher in northern Vasatch.
"In the minds of most people, dust is a natural aerosol. However, the size and frequency of airborne dust affects human activity, changing the landscape makes dust more likely for the wind, "said Skiles. "We know that since the settling of the West, dust has increased in the air. At the same time, due to the withdrawal of water, the levels of the lake also decrease, exposing even more dust. "
Dust is a global problem
In October, Skiles co-authored the article that reviewed the literature on the growing global issue of "light-absorbing particles" in the Nature magazine. The Climate Scientific Society has recognized the impact of aerosols that are clearly associated with human activity, such as soot, but still need to consider other particles that make the snow darker and accelerate melting.
"Snow is global in decline and it's not just because of the climatic climate – it's more complicated than that – the snow gets darker," Skiles said. "We know that in some places aerosols affect water resources and have a long-term impact on climate change. We also know that deposition levels will not decrease in the future. Although we still do not understand the exact size of the impact, we know that dust requires more attention. "
Skiles studied snow dust in Colorado Rockies, but he wants to keep looking at other mountain areas.
"I'm interested in watching in Wyoming, Montana and here in Yute because we need a regional perspective – we know that dust has a dramatic impact on snow melting in Colorado, but what's the impact on other places? If dust is not so important in these regions, what then controls the change of snow melting patterns? "She asked.