Thunderstorms and lightning play a key role in the chemistry of our atmosphere. Credit: NOAA
are targeting thunderstorms in Alabama, Colorado and Oklahoma this
spring to discover what happens when clouds suck air many miles into the
atmosphere from Earth’s surface.
Deep Convective Clouds & Chemistry (DC3) Experiment, which begins
in mid-May, will explore the influence of thunderstorms on air just
beneath the stratosphere, a region that influences Earth’s climate and
will use three research aircraft, mobile radars, lightning mapping
arrays and other tools to pull together a comprehensive picture.
tend to associate thunderstorms with heavy rain and lightning, but they
also shake things up at the top of the cloud level,” says National
Center for Atmospheric Research (NCAR) scientist Chris Cantrell, a DC3
“Their effects high in the atmosphere in turn have effects on climate that last long after the storm dissipates.”
past field projects have focused on thunderstorm details with only some
chemistry information, or on chemistry with limited data on storms, DC3
is the first to take a comprehensive look at both chemistry and
thunderstorm details, including air movement, cloud physics and
scientists leading the project are from NCAR, Penn State University,
Colorado State University, and the National Oceanic and Atmospheric
Administration (NOAA), with involvement by more than 100 researchers
from 26 organizations.
Funding for DC3 is from the National Science Foundation (NSF), NOAA and NASA.
of the key goals of DC3 is exploring the role of thunderstorms in
forming upper-atmosphere ozone, a greenhouse gas that has a strong
warming effect high in the atmosphere.
internal structure of thunderstorms and the lightning that accompanies
them differs considerably across the country,” says Brad Smull, director
of NSF’s physical and dynamic meteorology program. “That in turn
affects the chemical processes inside these storms.”
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 airmass 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.
ozone is difficult to track because, unlike most greenhouse gases, it
is not directly emitted by either pollution sources or natural
sunlight triggers interactions between pollutants such as nitrogen
oxides and other gases, and those reactions create ozone.
interactions are well understood at the Earth’s surface, but have not
been measured at the top of the troposphere, the lowest layer of the
atmosphere just below the stratosphere.
in thunderstorm clouds range from about 20 to 100 miles per hour, so
air arrives at the top of the troposphere, about 6 to 10 miles up, with
its pollutants relatively intact.
polluted airmasses don’t keep rising indefinitely because of the
barrier between the troposphere and stratosphere, called the tropopause.
“In the mid-latitudes, 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 underway.
fly again the next day to find the same air mass, using its distinctive
chemical signature to see how it has changed over time.
Pollution isn’t the only source of nitrogen oxides, the ozone precursor. Lightning strikes also produce nitrogen oxides.
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
DC3 investigators are looking at three widely separated sites in
northern Alabama, northeastern Colorado, and central Oklahoma to west
three 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.
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.
results will improve understanding of how storms produce lightning, and
of how to use lightning mapping data to improve storm forecasts and
three research aircraft will be based at Salina Municipal Airport,
Kan., a location central to all three study areas. Each day, they will
fly to whichever area has the most promising forecast for thunderstorms
suitable for study.
The NSF/NCAR Gulfstream V research aircraft will do the bulk of the high-altitude measurements.
a NASA DC-8 will fly as low as 1,000 feet above the ground, measuring
air flowing into the clouds at their bases as well as the chemistry of
third research aircraft, a Dassault Falcon 20E operated by the German
space agency will join DC3 for three weeks and fly especially close to
storm cores at high altitudes.
The multiple sites will enable the scientists to study different types of atmospheric environments.
has more trees and thus more natural emissions; the Colorado site is
sometimes downwind of Denver’s pollution; the Oklahoma and west Texas
site may offer clean air.
“The more different regions we can study, the more we can understand how thunderstorms affect our climate,” Barth says.
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 DC3 scientists the
opportunity to make major advances in understanding these chemical
Source: National Science Foundation