New Method for Three-Dimensional Imaging of Cirrus Clouds

Liou, K., University of California, Los Angeles

Cloud Distributions/Characterizations

Cloud Properties

Liou, K.N, S.C. Ou, Y. Takano, J. Roskovensky, G.G. Mace, K. Sassen, and M. Poellot, 2002: "Remote sensing of three-dimensional inhomogeneous cirrus clouds using satellite and mm-wave cloud radar data," Geophysical Research Letters 29(9): 1360.


Figure 1


Figure 1

ARM Data Enables the Development and Verification of a New Method for Three-Dimensional Imaging of Cirrus Clouds to Improve Climate Predictions

Cirrus clouds cover about 30% of the Earth's surface. Because ice crystals both reflect sunlight and absorb thermal energy emitted from the earth surface, accurate representations of cirrus clouds in climate models are critical to the simulation of the Earth's radiation budget. Recent technical advances in remote sensing allow researchers to view cirrus clouds simultaneously using satellite and ground-based instruments. A team of atmospheric scientists from the University of California at Los Angeles (UCLA), the University of Utah (UT) and the University of North Dakota (UND), led by Professor K. N. Liou of UCLA, has applied a new method to combine these two separate sets of observations of cirrus clouds and create a single three-dimensional (3-D) image of cirrus clouds (see figure 1), which could aid in climate prediction worldwide.

Cirrus clouds display substantial horizontal and vertical variability. Correct simulation of their radiative effects requires knowledge of not only bulk properties such as cloud fraction and thickness, but also of microphysical properties such as ice-crystal size and ice mass, which are spatially highly variable. The innovative remote sensing method developed by Liou and his team actually creates a 3-D view of the cirrus ice mass and ice-crystal size. They retrieve the 3-D cloud structure from the combined data using radiative transfer physics. The data for this study were gathered during the Spring 1997 Intensive Observation Period (IOP) at the U.S. Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) Program site in Oklahoma. In addition to the data from the NOAA satellite and the ARM cloud radar, scientists collected samples of ice mass and size in the cloud using a research aircraft. The Liou team used the remotely sensed data to create the first 3-D map of cirrus cloud structure and then validated the values of ice mass and size independently at specific locations using the aircraft measurements carried out in that same cloud.

This 3-D cloud structure provides valuable information for improving the representation of clouds and cloud effects in climate models, which are used in climate predictions. Research scientists can use this information to visualize and understand both the vertical and horizontal structure of cirrus clouds, and then model the transport of solar and thermal energy through the complex structure. This study was recently published in the May 15, 2002, issue of the Geophysical Research Letters (Liou et al., "Remote sensing of three-dimensional inhomogeneous cirrus clouds using satellite and mm-wave cloud radar data.") The paper has also been selected by the journal editors as the AGU Journal Highlight.

This study was funded primarily by the DOE ARM Program, with additional support from NSF and NASA. Key contributors include K. N. Liou, S. C. Ou and Y. Takano of UCLA, G. G. Mace and K. Sassen of UT, and M. Peollot of UND.