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January
25, 2007
AIRBORNE DUST
CAUSES RIPPLE EFFECT ON
CLIMATE FAR AWAY
When a small pebble drops into a
serene pool of water, it causes a ripple in the water in every
direction, even
disturbing distant still waters. NASA researchers have found a similar
process
at work in the atmosphere: tiny particles in the air called aerosols
can cause
a rippling effect on the climate thousands of miles away from their
source
region.
The researchers found that dust
particles from the desert regions in northern Africa can produce
climate
changes as far away as the northern Pacific
Ocean.
Large quantities of dust from North
Africa are
injected into the atmosphere by dust storms and rising air. Airborne
dust
absorbs sunlight and heats the atmosphere. The heating effect ripples
through
the atmosphere, affecting surface and air temperatures as the dust
travels.
"These highs and lows in air temperatures caused by radiation-absorbing
aerosols can lead to 'teleconnection’, which refers to
changes in weather and
climate in one place caused by events happening far away, often more
than half
way around the globe," said William Lau, Chief of the Laboratory for
Atmospheres at NASA's Goddard Space Flight Center, Greenbelt, Md., and
author
of a study published last fall in the American Meteorological Society's
Journal
of Climate. "North African dust can be lifted high into the atmosphere
by
storms and then transported across the Atlantic and Caribbean,
where its effect can be far-reaching."
From a climate point of view, aerosols can block solar radiation
(incoming heat
and light from the sun) from hitting the Earth's land surface. When
sunlight is
blocked, it can cause the Earth's surface to cool, and/or the aerosols
can
absorb solar radiation and cause the atmosphere in the vicinity of the
airborne
dust to get warmer.
According to Lau, researchers
thought for years that heat changes in the atmosphere from aerosols
only caused
local changes in temperatures. However, "we now know they may cause
more
than local changes to climate," he said. Lau's computer model indicates
that the heat changes caused by aerosols affect the heat balance in the
air
over North Africa.
That change in heat creates
large waves in the atmosphere that ripple as far away as Eurasia
and the North Pacific.
Researchers have created complex numerical models to simulate the
"still
waters" of the atmosphere during North African spring – a
season when
climate conditions are relatively calm with light winds and light rain.
Lau's team carried out a numerical model experiment that included
aerosol
forcing, and then another one with identical initial conditions and
lower
boundary conditions, except that the aerosol forcing is removed. By
comparing
the weather patterns in the two experiments, they can deduce the effect
of
aerosol forcing. They observed the aerosols made an impact far away
from their
source region. In setting up their experiment, the researchers chose
the
northern Sahara
Desert
in springtime, when the weather
conditions are relatively calm, allowing aerosols, like dust, to build
up more
in air.
An "atmospheric teleconnection" happens when unusual patterns of air
pressure and air circulation happen in one place, and the energy is
dispersed
over large distances around the globe to other places. An atmospheric
teleconnection can lead to changes in sea level pressure and
temperature around
the world. This study saw changes from North Africa through Eurasia
to the North Pacific.
Most interesting, Lau's team found that North African-dust
teleconnection led
to strong cooling over the Caspian Sea (a land-locked body of water
between Russia
and Europe) and warming over central and
northeastern Asia,
where man-made aerosol
concentrations are low.
"Elevated aerosols in large quantities such as dust from North Africa, or biomass burning
may have global impacts," said
Lau. "We expect to observe more and more real-world examples of this
teleconnection phenomenon with the high volume of aerosols generated by
nature
and human activities around the world."
For
more
information and images, visit:
http://www.nasa.gov/centers/goddard/news/topstory/2006/particle_ripple.html
For
more
information about atmospheric teleconnections, visit:
http://www.cpc.ncep.noaa.gov/data/teledoc/teleintro.shtml
Writer: Gretchen
Cook-Anderson, NASA Goddard Space Flight Center
##
Contact:
Lynn Chandler
NASA Goddard Space Flight Center
301-286-2806
Lynn.Chandler-1@nasa.gov
This text is
derived from:
http://www.nasa.gov/centers/goddard/news/topstory/2006/particle_ripple.html
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