On thin icege/gi

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.