Long, narrow bands of moving moisture in the sky, known as atmospheric rivers, contribute to heatwaves in the marine environment, according to a new study published in Nature Communications by researchers from Duke University's Nicholas School of the Environment. The study, which received funding from NASA, is the first to analyze the association between these "rivers in the sky" and marine heatwaves, paving the way for future research on the mechanisms at play and how climate change factors in.
Marine heatwaves are periods of abnormally high ocean temperatures that last for weeks or even months. Because many marine organisms acclimate to seasonal water temperatures, periodic spikes in ocean temperature can have severe ecological consequences, with repercussions for coastal communities and economies.
Atmospheric rivers, meanwhile, are transient weather systems that often cause extreme rainfall and flooding over land, such as in the western United States and western Europe. Before atmospheric rivers reach land, however, they spend most of their time over oceans, where they can influence sea surface temperatures through various processes that move heat around.
"We wanted to see if these interactions between atmosphere and sea surface might play a role in marine heatwaves," says Shineng Hu, an assistant professor of climate dynamics in the Nicholas School, who authored the study with postdoctoral associate Suqiong Hu.
The team used data collected from satellites, ships and other instruments to identify atmospheric rivers and marine heatwaves that occurred in the North Pacific and North Atlantic oceans, outside of the tropics, from 1982 to 2023. Both types of phenomena are known to be more active and severe in these regions than in other parts of the ocean.
Through statistical analysis, the team found a particularly strong association between atmospheric rivers and marine heatwaves. In winter, for example, unusually active atmospheric rivers occur a couple of days before marine heatwaves peak, suggesting that the former influence the latter. By contrast, in summer, fewer atmospheric rivers precede marine heatwaves.
"Whether atmospheric rivers promote marine heatwaves depends on how heat moves between the air and the ocean," Suqiong Hu says. "Cloud cover tends to increase with atmospheric rivers, causing the sea surface to cool. However, warm and moist air associated with atmospheric rivers cause the sea surface to warm up. These opposing mechanisms play out differently depending on the season and region."
The findings highlight the importance of understanding the role of temporary ocean-atmosphere interactions in future climate warming.
"Marine heatwaves have been stronger and more frequent under global warming, because the ocean absorbs most excess heat trapped by rising greenhouse gases. Atmospheric rivers also tend to become more intense as the air gets warmer and moister, according to our previous study . How interactions between these events might respond to climate change is what we are trying to understand next," Shineng Hu says.
