15 May 2017

A Novel, Finite-Amplitude Wave Activity Transformation Reveals New Insights on Water Cycle Variations and Extremes

The method identifies an increase in wet-versus-dry disparity in a warmer climate and reveals a unique characteristic of the atmospheric river.

Science

Precipitation, different from many geophysical processes, has a probability distribution that is far from normal, posing scientific challenges to understand how hydrological extremes would respond to future warming. A research team led by scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory developed a novel, finite-amplitude atmospheric wave activity analysis method for water vapor to study hydrological variations and extremes.

Impact

The novel, finite-amplitude wave activity analysis method for water vapor opens the door for new analyses to provide insights on hydrological variations and extremes that have important societal implications. When researchers applied the method to simulations of an aquaplanet (all-water world), they uncovered new insights on the role of atmospheric wave dynamics in the hydrological response to warming and revealed a unique characteristic of atmospheric rivers that has been linked to heavy precipitation events.

Summary

Building on the recent advent of the concept of finite-amplitude wave activity applied to geophysical fluids, researchers developed a novel, finite-amplitude wave activity transformation for water vapor and its budget equation. The transformation produced a quantity called water vapor wave activity and its source/sink that resembled a normal distribution, making it more amenable to linear analysis. The wave activity sink measured the wet-versus-dry disparity in net precipitation (precipitation minus evaporation). More notable, a strong linear relationship emerged between the hydrological disparity and the water vapor wave activity. Researchers used the relationship to explore the response of the hydrological cycle to warming in an aquaplanet, and they found that the wet-versus-dry disparity tended to increase globally because of warming. However, the change in disparity had a unique meridional distribution, which was largely attributed to wind changes. This underlines the importance of understanding how the atmospheric wave dynamics respond to warming to explain hydrological changes in the future. Meanwhile, the analysis unraveled a global reduction in the rate of the hydrological processes that are associated with the timescale for wave activity to cycle through the system. The wave activity analysis also helped reveal a unique characteristic of the atmospheric river: It brings moisture from tropical and subtropical regions to higher-latitude destinations leaking relatively little moisture as precipitation along the way, similar to rivers that transport water over land.

Contact
L. Ruby Leung
Pacific Northwest National Laboratory
Publications
Lu, J., Sakaguchi, K., Yang, Q., et al. "Examining the Hydrological Variations in an Aquaplanet World Using Wave Activity Transformation." Journal of Climate (2017). [10.1175/JCLI-D-16-0561.s1].