Published: 14 November 2011

10 years of data from ARM Southern Great Plains site corroborate satellite measurements; match model

A study published in Nature Geoscience this week reveals a trend that atmospheric scientists have been mulling for decades: the effects of aerosols on clouds and rainfall. Some studies have suggested that aerosols—tiny particles in the air, such as dust and soot—may make clouds “drier” while others studies suggest they may intensify storm systems.

According to Zhanqing Li, a professor of atmospheric and oceanic science at the University of Maryland and lead author of the study, the new study reveals impacts of an “unprecedented magnitude.”

“Under very dirty conditions, the mean cloud height of deep convective clouds is more than twice that of the mean height under pristine conditions. Yet, the probability of heavy rain increases by 50 percent moving from clean to dirty conditions, whereas the chance of light rain is reduced by 50%,” said Li.

The findings, based on a 10-year data set of ground-based measurements from the ARM Southern Great Plains site in Oklahoma, corroborate an analysis of NASA global satellite products. Matching results were obtained from simulations by a cloud-resolving model. This is a computer model that simulates the regional-scale dynamics that occur in clouds, as opposed to the large-scale processes simulated in global climate models.

The work by Li and his research colleagues signifies the importance of long-term data sets for climate-relevant studies, as well as the need for measurements from regions of the world most affected by increasing levels of atmospheric aerosols, such as those obtained in these recent ARM field campaigns:

• Ganges Valley Aerosol Experiment, Nainital, India – 2011
• Clouds, Aerosol and Precipitation in the Marine Boundary Layer, Graciosa Island, Azores – 2009-2010
• Study of Aerosol Indirect Effects in China, Shouxian, China – 2008
  • Journal of Geophysical Research-Atmospheres, Special Issue

For more information on the recent study, read the joint press release from Maryland, Brookhaven National Laboratory, and Pacific Northwest National Laboratory.

Article Reference: Li, Z., F. Niu, J. Fan, Y. Liu, and D. Rosenfeld, Y. Ding. 2011. “The long-term impacts of aerosols on the vertical development of clouds and precipitation.” Nature Geoscience, doi: 10.1038/NGEO1313.