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STUDY
OF CLOUD ICE CRYSTALS MAY IMPROVE CLIMATE CHANGE FORECASTS
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Studies
of cirrus clouds by some 450 scientists may lead to improved forecasts of future
climate change. During
July in southern Florida, scientists from NASA's Goddard Space Flight Center,
Greenbelt, Md. will join others to investigate high tropical cirrus clouds composed
of tiny ice crystals.The researchers 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?"
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2 | | | 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 in July. They plan to analyze
and report their data by the spring of 2003. "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.
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3 | | | The
effort is called the Cirrus Regional Study of Tropical Anvils and Cirrus Layers
- Florida Area Cirrus Experiment (CRYSTAL-FACE). Participants include researchers
from various NASA centers including Ames; Goddard Space Flight Center, Langley
Research Center, Hampton, Va.; and the Jet Propulsion Laboratory, Pasadena, Calif.
Other participating researchers are from the National Oceanic and Atmospheric
Administration, the National Center for Atmospheric Research, Boulder, Colo.,
and various universities and companies. 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.
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4 | | | "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.
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5 | | | 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 the Aqua satellite. NASA's
Goddard Space Flight Center contributed most of the payload for the ER-2 aircraft,
including the Cloud Radar System (CRS), Cloud Physics Lidar (CPL), ER-2 Doppler
radar (EDOP), dropsonde system, and Conical Scanning Submillimeter-wave Imaging
Radiometer (CoSSIR). Lidar
provides information on cloud and aerosol optical properties (the amount of light
they reflect and scatter), as well as internal cloud structure. "CRYSTAL
is the first field experiment to combine the lidar and radar data to produce a
complete remote sensing image of the atmosphere," said Goddard's Matthew
McGill, a principal investigator for the Cloud Physics Lidar instrument. The lidar
has sensitivity to thin clouds that the radar does not, and the radar can penetrate
thick, convective systems that the lidar cannot. The lidar-radar data products
will also be combined with other instruments to provide a complete study of the
atmosphere. The
lidar-radar data product being obtained during this mission is a near-perfect
simulator for the product that will be obtained from the upcoming satellite missions
of CALIPSO and CloudSat.
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