Press Release:
Scientists at the National Center for Atmospheric Research (NCAR) and
other organizations are targeting thunderstorms in Alabama, Colorado,
and Oklahoma this spring to discover what happens when clouds suck air
up from Earth’s surface many miles into the atmosphere.
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| Thunderstorm in eastern Colorado. (Photo by Bob Henson.) |
The Deep Convective Clouds and Chemistry (DC3) experiment, which
begins the middle of this month, will explore the influence of
thunderstorms on air just beneath the stratosphere, a little-explored
region that influences Earth’s climate and weather patterns. Scientists
will use three research aircraft, mobile radars, lightning mapping
arrays, and other tools to pull together a comprehensive picture.
“We tend to associate thunderstorms with heavy rain and lightning,
but they also shake things up at the top of cloud level,” says NCAR
scientist Chris Cantrell, a DC3 principal investigator. “Their impacts
high in the atmosphere have effects on climate that last long after the
storm dissipates.”
Past field projects have focused on either the details of
thunderstorms but with limited data on the atmospheric chemistry behind
them, or on the chemistry but with little detail about the storms
themselves. DC3 is the first to take a comprehensive look at the
chemistry and thunderstorm details, including air movement, cloud
physics, and electrical activity.
Funding for DC3 comes from the National Science Foundation (NSF),
National Oceanic and Atmospheric Administration (NOAA), and NASA. The
scientists leading the project are from NCAR, Pennsylvania State
University, Colorado State University, and NOAA, with involvement by
more than 100 researchers from 26 organizations.
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| The DC3 field project will deploy a variety of airborne and ground-based instruments to study thunderstorms. Click on image for a larger version. Image Credit: UCAR. |
On the trail of ozone
One of the key goals of DC3 is exploring the role of thunderstorms in
forming upper-atmosphere ozone, a greenhouse gas that has a
particularly strong warming effect high in the atmosphere.
“When thunderstorms form, air near the ground has nowhere to go but
up,” says NCAR scientist Mary Barth, a principal investigator on the
project. “Suddenly you have an air mass at high altitude that’s full of
chemicals that can produce ozone.”
Ozone in the upper atmosphere plays an important role in climate
change by trapping significant amounts of energy from the Sun. However,
ozone is difficult to track because, unlike most greenhouse gases, it is
not directly emitted by either pollution sources or natural processes.
Instead, sunlight triggers interactions between pollutants such as
nitrogen oxides and other gases, and those reactions create ozone. These
interactions are well understood at Earth’s surface, but they have not
been measured at the top of the troposphere, the lowest layer of the
atmosphere, which is just below the stratosphere.
Updrafts within thunderstorm clouds range from about 20 to 100 miles
(about 30-160 kilometers) per hour, so air arrives at the top of the
troposphere, about 6 to10 miles (10-16 kilometers) up, with its
pollutants relatively intact. The polluted air masses don’t keep rising
indefinitely because of the barrier between the troposphere and
stratosphere, called the tropopause.
“In the midlatitudes, the tropopause is like a wall,” says Barth. “The air bumps into it and spreads out.”
The DC3 scientists will fly through these plumes to collect data as a
storm is under way. Then they’ll fly through the same air mass the
next day, using its distinctive chemical signature to see how it’s
changed over time.
Pollution isn’t the only source of nitrogen oxides, the ozone precursor. Lightning strikes also produce nitrogen oxides.
"We are pretty sure lightning is the largest natural source of nitric
oxide," says NOAA National Severe Storms Laboratory scientist Don
MacGorman. "It is important to know the naturally occurring
contribution."
Three sites, three airplanes
The DC3 investigators are looking at three widely separated sites in
northern Alabama, northeastern Colorado, and central Oklahoma to west
Texas. All the sites have existing weather instrumentation on the
ground, including dual-Doppler research radars, lightning mapping
arrays, and balloon launches to measure the state of the atmosphere from
the ground to the stratosphere.
Scientists at each of the sites will combine data from radars with
Doppler capabilities (for wind information) and polarimetric
capabilities (for wind and cloud particle information) with lightning
mapping arrays to better understand both how storms produce lightning as
well as how to use lightning mapping data to improve storm forecasts
and warnings.
“The internal structures of thunderstorms—and the lightning that
accompanies them—differ considerably across the country,” says Brad
Smull, NSF program director for physical and dynamic meteorology. “This
in turn affects the chemical processes occurring inside these storms.”
The three research aircraft will be based at Salina Municipal Airport
in Kansas, a location central to all three study areas. Each day, the
research team will fly to whichever area has the most promising forecast
for thunderstorms suitable for study.
The NSF/NCAR Gulfstream V research aircraft will undertake the bulk
of the high-altitude measurements. Simultaneously, a NASA DC-8 will fly
as low as 1,000 feet (300 meters) above the ground, measuring air
flowing into the cloud bases as well as the chemistry of the surrounding
air. The third research aircraft, a Dassault Falcon 20E operated by
DLR, the German aerospace agency, will join DC3 for three weeks and fly
especially close to storm cores at high altitudes.
Flying from multiple sites will enable the scientists to study
different types of atmospheric environments. Alabama has the most trees
and thus more natural emissions. The Colorado site is sometimes downwind
of Denver’s pollution, whereas the Oklahoma and west Texas site may
offer very clean air.
“The more different regions that we can study, the more we can understand how thunderstorms affect our climate,” Barth says.
Alex Pszenny, NSF program director for atmospheric chemistry, adds:
“The simultaneous chemistry measurements from three of the world's most
sophisticated research aircraft, combined with data from
state-of-the-art radar and lightning sensor technology, will give the
DC3 team the opportunity to make major advances in understanding those
chemical processes.”
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Sidebar
The argument that molecules are too heavy to make it into the upper atmosphere is a myth. As was mentioned in a previous post about Sherwood Rowland "the atmosphere is not stratified by molecular weight. It is well mixed due to convection in the troposphere and any chemical released at the surface can make it high into the atmosphere. Molecules are no match for air currents. Much heavier substances like dust can make it into the stratosphere."
_______________________________________________________________________
Sidebar
The argument that molecules are too heavy to make it into the upper atmosphere is a myth. As was mentioned in a previous post about Sherwood Rowland "the atmosphere is not stratified by molecular weight. It is well mixed due to convection in the troposphere and any chemical released at the surface can make it high into the atmosphere. Molecules are no match for air currents. Much heavier substances like dust can make it into the stratosphere."
