Study of Cloud Ice Crystals May Improve Climate Change Forecasts

Studies of cirrus clouds by some 450 scientists may lead to improved
forecasts of future climate change.

This month in southern Florida, scientists will investigate high tropical
cirrus clouds composed of tiny ice crystals. The scientists hope to
determine how the clouds form, how they limit the amount of sunlight
reaching the surface of the Earth and how they trap heat rising from the
surface and lower atmosphere. This key information will help improve
computer programs that forecast global climate change.

“Our objective is to find out how ice clouds affect global warming,” said
Eric Jensen, project mission scientist at NASA Ames Research Center in
California’s Silicon Valley. “The combination of measurements and computer
modeling studies will improve our understanding of how cirrus (clouds) may
change in response to climate change,” he said. “For example, as the surface
heats up and thunderstorms become more intense, will larger, thicker cirrus
clouds be formed?”

Scientists from NASA, other government agencies, academia and industry will
investigate cirrus clouds in Florida with the objective of reducing
uncertainties in forecasts of the Earth’s future climate. High, tropical
cirrus clouds are composed of tiny ice crystals that float at altitudes from
20,000 feet (6,096 meters) to 60,000 feet (18,288 meters). Scientists will
take measurements from a variety of aircraft and ground instruments for four
to six weeks beginning this month. They plan to analyze and report their
data by the spring of 2003. The effort is called the Cirrus Regional Study
of Tropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment
(CRYSTAL-FACE).

“Clouds are the largest source of uncertainty in computerized global climate
models,” Jensen said. “We want to measure the ice crystal sizes, cloud
optical depths and the heating or cooling of the Earth’s surface caused by
tropical cirrus clouds, particularly those generated by intense storms.”
Optical depth is a measure of the visual or optical thickness of a cloud.

Recent observations from NASA’s Terra satellite, with improved sensitivity
to detect cirrus cloud systems, suggest that cirrus are present more than
expected both temporally and spatially across the planet. Cirrus may act to
warm or cool the planet and the tendency toward warming or cooling depends
on the extent, duration, thickness and location of the clouds.
A major scientific goal is to use cloud measurements from aircraft to
calibrate remote cloud measurements from satellites so characteristics of
clouds can be observed more accurately from the higher altitudes of orbiting
spacecraft. Better-calibrated satellite observations of clouds will result
in improved large-scale measurements of clouds because as satellites orbit
Earth, they can observe huge areas of the globe at once. These satellite
cloud measurements will enable scientists to make more accurate regional and
global cirrus cloud computer models that should reduce the uncertainty of
climate change predictions, Jensen said.

“We anticipate flights will be mostly over southern Florida, and
occasionally we will sample clouds over the ocean,” Jensen said.

Many of the scientists and aircraft involved in CRYSTAL-FACE will be based
at Key West Naval Air Facility, Fla., during the experiment. Six aircraft
types will carry instruments to measure cirrus clouds. The high-flying ER-2
(similar to a U-2), based at NASA Dryden Flight Research Center, Edwards,
Calif., will conduct remote sensing of cirrus clouds and environmental
conditions, as will the Proteus aircraft, built by Scaled Composites,
Mojave, Calif. Scientists will compare the ER-2 instrument readings with
similar satellite measurements.

The WB-57 aircraft based at NASA Johnson Space Center, Houston, will be
making in situ measurements of cirrus clouds and environmental conditions. A
Citation aircraft from the University of North Dakota will make in situ
measurements in the lower parts of cirrus ‘anvils.’ An anvil is an extensive
ice cloud that forms at the tops of deep thunderstorm clouds.

A P-3 aircraft, based at the Naval Air Station, Patuxent River, Md., and
provided by the Naval Research Laboratory, will use airborne radar to
measure cloud structure and intensity. A Twin Otter airplane from the Center
for Interdisciplinary Remotely Piloted Aircraft Studies, which is part of
the Naval Postgraduate School and is based at the Navy Airport near Fort
Ord, Calif., will make in situ measurements of aerosols and take other
readings. Ground-based instruments in the study include radar and other
instruments. Satellites included in the study will be GOES, Terra, Tropical
Rainfall Measuring Mission and Aqua.

In addition to Jensen, other scientists from NASA Ames will take part in the
CRYSTAL-FACE project. They include Andrew Ackerman and Katja Drdla, Jensen’s
co-investigators who are working on cirrus cloud computer modeling. Peter
Pilewskie of Ames and his colleagues will use instruments on the ER-2 and
Twin Otter aircraft to measure trapping of heat and reflection of sunlight
by clouds. Max Loewenstein’s experiment includes measurements of carbon
monoxide and methane. Paul Bui and others from Ames are responsible for
measurements from the WB-57 and ER-2 aircraft of temperature, pressure and
winds. Henry Selkirk and Leonhard Pfister are studying development and
movement of cirrus clouds. Selkirk also will be the lead forecaster for the
mission.

Participants include researchers from various NASA centers including Ames;
Goddard Space Flight Center, Greenbelt, Md.; Langley Research Center,
Hampton, Va.; and the Jet Propulsion Laboratory, Pasadena, Calif.
Participating government organizations include the Department of Defense
Office of Naval Research, the National Science Foundation, the National
Oceanic and Atmospheric Administration, the Department of Energy and The
National Polar-orbiting Operational Environmental Satellite System.

A complete list of participants is on the project Website at:
http://cloud1.arc.nasa.gov/crystalface/
Project manager Michael Craig of the Ames Earth Science Project Office is in
charge of the field campaign for NASA. CRYSTAL-FACE will be the largest
mission ever run by the Earth Sciences Project Office.

This research is part of NASA’s Earth Science Enterprise, a long-term
research effort that utilizes the unique vantage point of space to view our
home planet to better understand and protect life here, while exploring for
life in the universe. CRYSTAL-FACE will support data validation of NASA
satellite investigations, including EOS Terra and Aqua satellite missions
and the Tropical Rainfall Measurement Mission.

A fact sheet about the mission is on the World Wide Web at:
http://amesnews.arc.nasa.gov/factsheets/FS-02-03AR.html

Publication-size images are available on the Internet at:
http://amesnews.arc.nasa.gov/releases/2002/02images/cirrusclouds/clouds.html