from the field: Turbulence and pollution
over Mexico City is clearly evident
in this photo from the Basílica
of Guadalupe. (Photos by Carlye Calvin.)
It’s been a busy couple of months in the field
for NCAR. The HIAPER aircraft in its maiden campaign
performed flawlessly over California while, in the
Mexico City area, scientists gathered vital information
about air pollution.
Soaring over the Owens Valley in March and April, HIAPER
(High-performance Instrumented Airborne Platform for
Environmental Research) flew through areas of turbulence
known as mountain waves and aimed its instruments at
treacherous atmospheric whirlwinds, called rotors.
Its mission was part of a large, multidivisional and
multinational field campaign known as the Terrain-Induced
Rotor Experiment (T-REX), which collected data about
rotors and mountain waves, as well as atmospheric behavior
closer to the valley floor.
Meanwhile, ACD researchers and collaborators from around
the world studied air pollution in and around Mexico
City for the much-anticipated Megacity Impacts on Regional
and Global Environments (MIRAGE) field campaign. Their
objective was to determine how the pollution affects
regional and global air quality, climate, and ecosystems,
with an eye toward applying what they learn to other
megacities around the world.
Here’s a look at these two important studies.
High and low
Dan Kirshbaum (MMM)
stands by the REAL lidar during T-REX.
HIAPER won rave reviews from the T-REX team almost
from the moment that it took off from Jeffco on March
2 for the first of 13 flights to California. “It’s
an excellent platform that’s able to get up to
high altitudes, cruise for a long time, and adjust
to changes in flight conditions created by strong mountain
waves,” says EOL’s Jorgen Jensen. “As
far as the instrumentation on board, it has been very
reliable. I’m really impressed with how things
The HIAPER flights were an important component of T-REX,
which brought 60 scientists, technicians, and students
from across the United States and Europe to California’s
sparsely settled Owens Valley from March 1 to April
30. Researchers also flew two other aircraft at lower
altitudes and set up a large ensemble of ground instruments.
The research team, led by Vanda Grubiić of
the Desert Research Institute, picked the region because
it has the steepest topography in the continental United
States, with Owens Valley sitting some 9,000 feet (about
3,000 meters) directly below the highest peaks of the
adjacent Sierra Nevada mountains. The mountains spawn
atmospheric waves that propagate upward and can “break” into
the stratosphere, creating clear-air turbulence. The
strong wind shear and turbulence in these waves and
altitude rotors play havoc with aircraft.
Maclean (bottom) and John Militzer remove
an antenna from a 110-foot flux profiling
tower in the Owens Valley.
HIAPER flew through the waves in the upper troposphere
and lower stratosphere at altitudes of up to 45,000
feet (13,700 meters). It joined aircraft from the University
of Wyoming and the United Kingdom, which flew at lower
elevations and gave scientists additional views of
the mountain waves, rotors, and valley phenomena.
Researchers on HIAPER released dropsondes to collect
data on the rotors. The aircraft also carried an array
of atmospheric chemistry samplers to provide insights
into the ways that mountain waves moved air masses
between the stratosphere and the underlying troposphere.
Heightened ozone levels indicated that air was coming
down from the stratosphere, where ozone concentrations
tend to be higher; heightened carbon monoxide levels,
on the other hand, indicated that air was rising
from the lower troposphere. “Ozone and other
tracers provided us with nice correlative signatures
of mountain waves,” says ACD’s Laura Pan.
To study airflow, the research team also used an array
of ground-based instruments, including radars, lidars,
automated weather stations, wind profilers, and balloons.
The project didn’t focus just on higher altitudes.
On days when HIAPER wasn’t flying, researchers
examined turbulent eddies of air just above the levels
of trees and bushes. Among the instruments they used
was a suite of three hot-film anemometers, developed
at NCAR, that took 2,000 measurements per second of
winds in three dimensions.
“We’re looking at turbulence on all scales,
from mountain waves that reach up to the stratosphere
down to very small-scale turbulence near the surface,” explains
EOL’s Greg Poulos, one of the project’s
principal investigators and the ground-based instrument
coordinator. “It’s a very complex study.”
The weather generally cooperated, bringing in high
winds with a train of potent Pacific storms. Researchers
didn’t always know the exact timing and strength
of the airflow features in advance—which is part
of the reason for the experiment in the first place—but
their location, at least, was somewhat predictable. “Here
we know where the turbulence is more likely to occur,
relative to the mountain barrier. In severe storms,
it sneaks up on you,” says EOL’s Dick Dirks,
the field operations director.
investigator Joach Kuettner (JOSS) exits
the HIAPER aircraft.
Despite HIAPER’s excellent performance, researchers
did encounter some challenges. On the ground, team
members found themselves contending with gusty winds
that pushed around instruments and researchers alike.
And on HIAPER, the team had to make adjustments to
sensors and overly noisy amplifiers. “These are
normal problems when you initially instrument a new
aircraft,” Jorgen explained.
But perhaps the greatest challenge was coordinating
the aircraft. As Greg puts it: “If you can envision
three airplanes stacked on top of each other flying
around in coordinated fashion, with two of them releasing
dropsondes and trying to avoid the other airplanes,
while working around the sensitive national park lands
in this area, that was a really significant challenge
On March 1, several dozen staffers, most from ACD
and EOL, descended upon Mexico City for the MIRAGE
field campaign. Working with collaborators from around
the world, they took a close look at the chemistry
of the city’s notorious air pollution.
The researchers didn’t have to search far to
find the justification for their study. “Overall,
we found an amazing haze everywhere, especially over
the city but also outside it,” says ACD’s
Sasha Madronich, one of the principal investigators. “It
was a great mixture of different pollution conditions,
including urban pollution, smoke from regional forest
fires, and dust events.”
The field campaign included air and ground components,
with researchers measuring both aerosols (airborne
particles of dust, soot, and other pollutants) and
gaseous pollutants (including ozone, nitrogen oxides,
carbon monoxide, sulfur dioxide, and hydrocarbons and
their oxidation products).
Hannigan (left) and Michael Coffey, working
in a trailer outside Mexico City, record
the absorption of infrared solar radiation
in the atmosphere. Such information is
used to determine levels of gases in
One of the biggest surprises during the campaign
was the extent of active particle production the
team observed in the atmosphere—that is, gases
condensing to form particles. The especially tiny
particles common in highly polluted areas can damage
human lung tissue and affect global climate.
“You’d expect in a very polluted location
not to have particle production,” explains ACD’s
Alex Guenther, who was stationed at a ground site outside
Mexico City. “What happens in a polluted
atmosphere is that you already have so many particles
in the air that the gases attach to existing particles.
But we observed particle production going on at the
ground site, and that was something unexpected.”
One of the researchers’ goals will be to determine
if the city’s exceptionally high level of pollution
actually changes the underlying chemistry of particle production.
ACD’s Jim Smith ran an experiment at the ground
site to look at how quickly particles of different
sizes take on water and turn into cloud droplets, since
the formation of clouds can impact climate. “The
experiments worked out as well if not better than expected,” he
From the air, researchers aboard the NSF/NCAR C-130
aircraft made multiple flights to transect the plume
of air pollution that blows out of Mexico City, usually
spreading northeast due to prevailing winds.
EOL’s Ed Ringleman at the controls
of the C-130 during MIRAGE.
“We didn’t see the flow to the northeast
as often as we had thought, but we had a much more
varied situation,” says MMM’s Bill Skamarock,
who ran the Weather Research and Forecasting model
(WRF) during the campaign to predict the plume’s
movement. “But the model performed well and
we were able to find the plume, more often than not,
where we expected.”
The aircraft team logged 88 hours of flight time in
all, on some occasions following the plume all the
way to the Texas coastline and the Yucatan peninsula.
Five other research aircraft were also in the air as
part of MILAGRO, an umbrella campaign of which MIRAGE
was one component. “Aircraft controllers
in Mexico were extremely helpful in coordinating six
airplanes buzzing through their airspace,” Sasha
The logistical complications of transporting equipment
across the U.S.-Mexico border proved to be the biggest
challenge during the field campaign. “Things
were a little slow getting started because we had issues
with shipments arriving late, but eventually everything
made it,” Sasha says.
From Mexico City, the C-130 flew directly to Seattle
for INTEX-B (Intercontinental Chemical Transport Experiment-B),
another of the four MILAGRO field campaigns. The main
goal of INTEX-B was to quantify the transport and evolution
of air pollution from Asia across the Pacific Ocean
to North America, and assess its implications for regional
air quality and climate.
• by David
Hosansky and Nicole Gordon
On the Web
In this issue...
from the field: Turbulence and pollution
and climate change
program is a star
Gilman wins Hale Prize
the helm of ESSL
Digital Image Library
Just One Look
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