As alpine mountaineers are all too aware, the sun can be brutally fierce atop snow-capped peaks.
Preliminary data from the weather stations on Mount Everest suggests this effect is amplified to an astounding degree at the top of the world, creating what could be some of the most intense illumination anywhere on Earth's surface.
This epic lighting does more than give hikers nasty sunburns. In a warming world, it might be hastening ice melt atop the world's highest mountains and impacting glaciers in ways scientists do not fully understand.
Presented at the American Geophysical Union annual meeting in San Francisco on Friday, the data is among the first scientific results to emerge from the National Geographic Society's and Rolex's Perpetual Planet Extreme Expedition to Everest, a multidisciplinary effort to study climate change atop the world's tallest mountain.
As part of the field excursion last spring, researchers installed a network of five automatic weather stations at elevations of up to 27,600 feet (8,412 meters), which includes the two highest weather stations on the planet.
These stations are helping to fill a critical gap in our understanding of high alpine meteorology and climate: Before their installation, the highest operating weather station the researchers knew of sat atop nearby Mera Peak, at a paltry altitude of about 21,000 feet (6,400 meters).
"There's still a lot of ice in the Himalayas above that altitude," said Tom Matthews, a climate scientist at Loughborough University in Britain and the meteorology co-lead for the expedition. "It's a monumental data gap."
All five stations are collecting data on air temperature, pressure, relative humidity and wind speed. Every station except for the highest one is outfitted with a net radiometer, an instrument that measures incoming and outgoing radiation, and the lower stations also carry rain gauges and present weather sensors.
Every day, the solar-powered stations beam their data via satellite links so that it can be uploaded in near-real time to the National Geographic Society's Perpetual Planet website. As of this week, the data is also being shared on social media by an Everest weather Twitter bot.
One of the key motivations behind the weather-station network is to better understand the amount of energy available to melt snow and ice in high alpine environments.
As Matthews explained, the highest Himalayan peaks get incredibly sunny both because there is less atmosphere to attenuate the light and because of their near-equatorial latitude.
While Everest hikers experience this viscerally, becoming overheated when the air temperature is close to freezing, solar radiation often is not accounted for when scientists model ice loss, Matthews said. Without available data, scientists may assume ice melt is driven solely by the air temperature.
But early returns from the new weather-station network suggest the sun is a truly dazzling force atop Everest, and its ice-melting power needs to be considered.
In some cases, Matthews said, the stations have registered levels of solar radiation equal to or exceeding the solar constant - that is, the amount of sunlight scientists expect to see at the outermost limits of Earth's atmosphere.
The researchers suspect this unearthly luminescence is the result of sunlight getting ping-ponged around by snow and ice as it falls on Everest's frozen spires.
"It's like a microwave, basically," Matthews said.
The data has not yet been published in a peer-reviewed journal. But if the findings hold up, Matthews says it could mean there is significant melt occurring hundreds of feet above the point where air temperatures drop below freezing.
Extrapolated across High Mountain Asia, "there could be thousands of square kilometers experiencing melt that we didn't know about," he said.
It is helpful to have more direct observations of weather at these extreme elevations, said Surendra Adhikari, an Earth scientist at NASA's Jet Propulsion Laboratory who was not involved in the new research.
While scientists have long understood that solar heating plays a role in glacial melting and that the effect increases with altitude, "we don't have a good idea of the size of that amplification," he said.
At very high altitudes, much of the meltwater produced by the sun is likely refreezing in place as it percolates into the snow. But that it still an important process to account for, said Joseph Shea, an alpine scientist with the University of Northern British Columbia Faculty Association who also was not involved in the analysis.
As this water refreezes, it releases heat energy and fills in air pockets, causing the surrounding snow and ice to become warmer and denser.
This may be impacting the long-term evolution of alpine glaciers in ways that are not being captured by models.
"If you're modeling melt, you want to account for all of these energy influxes," Shea said. "It's really hard to do when we don't have data."
Sorting out the various processes driving ice loss in the Himalayas has never been more urgent. These glaciers, whose water nourishes lands home to over a billion people, are receding at an alarming rate as global temperatures rise.
The region is often referred to as the "Third Pole", because of the huge volume of ice present there.
A groundbreaking report published earlier this year concluded that glaciers across the Hindu Kush Himalayan region could shrink in size by a third even if the ambitious 1.5-degree Celsius (2.7 degrees) global warming target is reached.
In addition to sunlight, the weather station data will provide critical insight into how much and when precipitation is falling on the mountains, as well as the role of the Asian monsoon, which is also affected by climate change.
With a few years' worth of data, Matthews and his colleagues are hoping to be able to say more about how the timing and intensity of monsoon precipitation impacts Earth's highest glaciers.
Before any of that can happen, however, the weather stations will face their biggest test yet: a winter atop Mount Everest. Matthews said he expects to see temperatures at the higher stations plunge below minus-40 degrees in the coming weeks and months.
Because the depths of winter also bring the fiercest winds of the year, a new world record wind chill "is on the cards," he said.
The weather stations are drilled into the bedrock and rated to withstand winds of nearly 240 mph (386 km/h). There is a small concern that there could be faster winds at such lofty heights, but the main worry is wind blowing rocks that would disable critical instrumentation or a solar panel.
"The big concern is really strong winds that do things to the station we can't plan for," Matthews said.
So far, all stations are holding up well. "The sensors seem to be functioning fine," he said. "But this is the moment of truth season."
The Washington Post
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