Now, a new study published in 'Nature Communications' offers a fresh approach. Da Yang, assistant professor of geophysical sciences at the University of Chicago, and his colleague Hing Ong, a former postdoctoral researcher now at Argonne National Laboratory, have developed an equation designed to clarify the forces driving atmospheric rivers. This new model could provide greater accuracy in forecasting such events, especially as climate change influences weather patterns.

A global weather driver
Atmospheric rivers are long, narrow corridors of moist air that transport water vapor from the tropics toward higher latitudes. These "rivers in the sky" can carry as much moisture as 15 times the flow of the Mississippi River, bringing heavy rain, snow, and intense winds. In California, for example, they deliver up to half of the state's yearly rainfall. While major events can lead to damaging floods and landslides, less intense atmospheric rivers also play a beneficial role in alleviating droughts and replenishing reservoirs.

Although these phenomena are prominent along North America's west coast, atmospheric rivers are a worldwide occurrence. Commonly observed moving from west to east, they are present in both northern and southern midlatitudes at any time. However, a robust framework for understanding how an atmospheric river's strength and trajectory evolve over time has been lacking.

"Double the insight"
Traditionally, scientists use a metric called integrated vapor transport (IVT) to monitor and track atmospheric rivers, which quantifies the flow and speed of water vapor. While this is useful for tracking, a more comprehensive equation is needed to understand the dynamics governing these systems. Yang's team introduced a variable known as integrated vapor kinetic energy (IVKE), which combines wind energy and moisture levels into a single quantity.

According to Yang, IVKE provides "an intuitive, first-principle-based governing equation that reveals what strengthens or dissipates an atmospheric river and explains its eastward movement." Unlike simple monitoring metrics, this equation explains underlying processes, enhancing real-time forecasting.

In testing, the team found that an atmospheric river's strength often rises as potential energy shifts into kinetic energy, while it weakens due to condensation and turbulence. Its movement eastward results from the horizontal flow of kinetic energy and moisture. The insights from this framework offer a stronger foundation for understanding these systems in real-time.

Implications for weather and climate adaptation
The National Oceanic and Atmospheric Administration (NOAA), which leads atmospheric river monitoring in the U.S., could benefit from Yang's approach. This new framework complements NOAA's IVT analyses, adding physical insights that can enhance the reliability of extreme weather forecasts and support improvements to forecast models.

Yang noted the potential impact of climate change on atmospheric rivers, stating, "We know that with climate change, the amount of water vapor is increasing. If circulation patterns stay consistent, we may expect stronger individual atmospheric rivers." Future studies will explore this link further. Yang's team, including new postdoctoral researcher Aidi Zhang, plans to use the IVKE framework to analyze climate change effects on atmospheric rivers.

Research Report:Though new to this specific field, Yang's broader expertise includes the study of tropical convective storms. Having spent 15 years in California, he developed an interest in atmospheric rivers and is now shifting his focus to these midlatitude phenomena.

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