Dust from the Copper Valley River as seen from space. Credit: You must credit: USGS/NASA Landsat
Giant dust storms in the Gulf of
Alaska can last for many days and send tons of fine sediment or silt into the
atmosphere, and it is having an impact on the global climate system, say
scientists.
The storms are so extensive they
can be seen by satellites orbiting the Earth. An image captured by the Landsat
satellite in 2020 shows dust blowing out of the valley and over Alaska's south
coast.
Exactly how the dust may be
influencing the global climate system is not yet clear, although new research from the University of Leeds
and the National Center for Atmospheric Science suggests the effect is bigger
than previously thought.
How ice forms in clouds
At a low enough temperature, the
silt—microscopic fragments of rock, minerals and vegetation—act as ice
nucleating particles, which encourage the formation of ice crystals in clouds.
Whether ice formation in clouds
will add to global
warming or help
cool the planet depends on how much ice they contain, how many ice nucleating
particles are present and the nature of those particles.
In a paper, titled "Southern
Alaska as a source of atmospheric mineral dust and ice-nucleating
particles," published in the journal Science Advances, the
research team argue that more research is needed to understand the role that
dust plays in the complex global climate system.
Dust storm in the Copper River Valley in Alaska.
Credit: Sarah Barr
Research has focused on Saharan dust
Previous research has focused
on dust particles whipped up into the atmosphere from storms in
the Sahara and across Africa and Asia, all of which are at mid to low latitudes
and involve dust generated from desert environments.
The researchers at Leeds took a
different approach and decided to look at a high-latitude source of dust. They
analyzed dust coming from the Copper River Valley on the south coast of Alaska,
which extends for more than 275 miles. The river is estimated to transport 70
million tons of glacial sediment every year.
During periods of low water—in the
summer and autumn—the silt is picked up by winds and carried over hundreds of
miles across north America, reaching altitudes where it can cause ice formation
in clouds.
Unlike the dust from Sahara,
however, dust particles from the Copper Valley River will contain a greater
volume of biological material, deposited by the rich vegetation and wildlife
that live in the region.
Dust storm, Copper River Valley, Alaska. Credit: Sarah Barr
Ice formation in clouds
Dust particles in the atmosphere
are important agents in ice formation.
In the absence of dust, water in
clouds can remain in liquid form even though temperatures may be well below
freezing.
Professor Benjamin Murray, an
Atmospheric Scientist in the School of Earth and Environment at Leeds who
supervised the study, said, "Only a small fraction of the dust particles
in the atmosphere has the capacity to nucleate ice and we are only just
starting to understand their sources and global distribution.
"Whether a cloud becomes more
or less reflective of sunlight depends on how much ice is in them, so we need
to be able to understand and quantify the various sources of ice-nucleating
particles around the globe.
"At present, climate models
tend not to represent these high-latitude sources of dust, but our work
indicates that we need to."
During the investigation, Sarah
Barr and Bethany Wyld, doctoral researchers in the School of Earth and
Environment at Leeds, collected samples during dust storms. The material was
later analyzed in the laboratory and compared to the types of dust particles
that originate from desert environments.
Dust storm, Copper River Valley, Alaska. Credit: Sarah Barr
Dust storm, Copper River Valley, Alaska. Credit: Sarah Barr
They
found that the particles from Alaska were more effective in forming ice than
the dust that comes from the Sahara, driven by the presence of microscopic
fragments of biogenic substances, particles that would have been produced by
living organisms.
In contrast, particles of a mineral
called potassium feldspar are believed to be the main ice nucleating agent in
dust from the Sahara and locations in mid to low-level latitudes.
Ms Barr, the lead author of the paper,
said, "We knew that deserts like the Sahara are very important at
supplying ice-nucleating particles to the atmosphere, but this paper shows that
river deltas like the Copper River Valley are also very important.
"Huge quantities of dust are
emitted from places like the Copper River, and we need to understand these
emissions to improve our climate models."
Source: Examining the role dust storms play in the world's climate (phys.org)
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