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NASA scientists have performed the first multi-year study
using satellite data to measure the 3-D distribution of dust
that travels from the Sahara Desert to the Amazon rainforest.
The Sahara is the world's largest desert.
At more than 3 million square miles,
it's almost the size of the continental United States.
Each year, Saharan dust is lifted from the ground,
and transported by winds on a 3000-mile journey
across the Atlantic Ocean.
A portion of the dust collects in the Amazon basin
—the largest rainforest on the planet.
Although dust particles are small,
no larger than around a tenth of the width of a human hair,
they form massive plumes that can be seen from space.
NASA's CALIPSO satellite was launched in 2006
to study the vertical structure of clouds and particles
in Earth's atmosphere.
CALIPSO observations from 2007 through 2013
show that on average,
182 million tons of dust leaves Africa each year.
Of this amount, about 27 million tons
is deposited in the Amazon basin.
Sahara dust contains phosphorus,
which is an important nutrient for plants.
In the tropic region, the phosphorus is quite limited.
So it's important to estimate how much dust
from the desert is transported to the Amazon.
The study shows Saharan dust adds phosphorous to the soils
that help compensate for losses
due to surface runoff and floods.
However, the amount of dust transported to the Amazon
changes from year to year.
According to the study, this variation is closely associated
with changes in rainfall in the Sahel,
a belt of semi-arid land just south of the Sahara.
When the Sahel was dry, the dust transport to the Amazon
in the next year would increase.
When it was wet,
dust transport would decrease.
Using satellites to get a clear picture of dust is important
for understanding, and eventually using computers to model
where that dust will go,
now and in future climate scenarios.


NASA | Satellite Tracks Saharan Dust to Amazon in 3-D

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serena 2018 年 11 月 20 日 に公開
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