Cloud Model Developed at Colorado State University Leads to New Discovery, Improved Understanding of Earth’s Climate

Scientists take cover when they mix stuff that doesn’t inherently go together.

But Colorado State University researchers David Randall and Charlotte DeMott were pleasantly surprised when they learned that a new computer model realistically represented weather changes in both the atmosphere and ocean when paired with an ocean model for the first time.

Computer modeling may sound hum-drum, but the results of the groundbreaking study – published in early January of this year in the American Geophysical Union’s prestigious Geophysical Research Letters – mean that researchers have taken a major leap toward understanding and predicting climate change and weather patterns. The paper was selected by the AGU as an “AGU Journal Highlight.”

The lead author of the paper is Cristiana Stan, a former graduate student of Randall’s, who is a research scientist at the Center for Ocean-Land-Atmosphere Studies (COLA, a non-profit research center in Maryland). “Cristiana took the initiative to couple the atmosphere and ocean models, and begin the coupled run,” said Randall. “We were surprised and intrigued to hear that she had taken such a bold step, and we were surprised again, pleasantly, when we saw how good her results were.”

Other authors in addition to Randall and DeMott include representatives of the State University of New York at Stony Brook (SUNYSB), COLA, and George Mason University.

All are members of the Center for Multiscale Modeling of Atmospheric Processes – a $19 million, multi-institutional Science and Technology Center based at Colorado State’s renowned Department of Atmospheric Science. Several dozen organizations and universities are members of the center with co-principal investigators at the San Diego Supercomputer Center and the National Center for Atmospheric Research in Boulder.

The atmosphere model, developed at Colorado State by Marat Khairoutdinov, now a professor at SUNYSB, uses a higher-resolution sub-model to simulate a collection of clouds in each of the thousands of "grid columns" of a global atmospheric model. The high-resolution model provides statistics for a sample of the clouds in the grid column, just as an opinion poll collects statistics based on the views of a sample of the population.

Scientists have always struggled to represent the physical and chemical processes of clouds, including precipitation, strong cloud-scale motions and radiation. It has been especially difficult to realistically simulate the interaction between cloud systems and the global-scale circulation of the atmosphere. Models are evaluated by comparison with actual observations of weather and climate.

“Cristiana’s coupled ocean-atmosphere model does a good job simulating El Niño – much better than the earlier model it was derived from,” said Randall, professor of atmospheric science at Colorado State since 1988 and principal investigator and director of the center. “El Niño is something that the atmosphere and the ocean do cooperatively. The climate of the atmosphere model became more realistic when it was coupled with the ocean model. That’s unusual, surprising, and very pleasing.”

DeMott, who analyzed some of the model results for the AGU paper, said the coupled model greatly improved the simulation of the Asian monsoon, which brings rainfall to one billion people on the globe.

“Not only are we putting the rainfall in the correct locations, but we’re also getting monsoon onsets and breaks – periods of lighter rain – right,” DeMott said.