Thin clouds high in the upper troposphere, like cirrus
clouds, may have a significant influence on Earth’s climate
and enhance the “greenhouse effect” by absorbing more of
the sun’s radiation than they take in. Unknown is how ice
crystals in these clouds absorb and reflect radiant energy
and enhance the amount of radiant energy emitted toward
the earth’s surface.
Pacific Northwest National Laboratory scientists who
are part of a science team supported by the Department
of Energy’s Atmospheric Radiation Measurement Program
have found that upper tropospheric clouds cannot be
detected by most remote sensors. This is unfortunate
because these clouds, which are found 9 miles above
sea level, may contribute significantly to the
radiative heating of the upper troposphere. To better understand the properties of these clouds,
the scientists need to know the size, shape, density and
microphysical properties of the ice crystals within the cloud.
Upper tropospheric clouds are difficult to measure because
they are continuously changing and their size distribution
and habit are not well characterized.
To understand these types of clouds, scientists rely on a
variety of complex mathematical formulas—called retrieval
algorithms—to estimate the microphysical properties of
clouds. The ground-based algorithms are compared with in
situ measurements made by airborne sensors and satellite-based
algorithms. Accurate retrievals are important for understanding
the radiative feedback of high clouds and parameterization
development for global climate models. Scientists will use these
results to help develop combined retrievals that choose the best
algorithm based on atmospheric conditions.
The Department of Energy's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time.