Purdue researchers use Rossby waves to predict heatwaves
03-18-2024
The next giant leap in predicting weather
Understanding why heatwaves happen is crucial. Heatwaves have devastating consequences across the world. Prolonged exposure to heat can have significant impacts on health, ecosystems, water resources, and even infrastructure.
Researchers Valentina Castañeda, PhD student, and Lei Wang, assistant professor, from Purdue University’s Department of Earth, Atmospheric, and Planetary Sciences, believe they have found a strong indicator for the prediction of heatwaves. The team uses Rossby waves to predict heatwave events. They recently published their results in the American Geophysical Union’s JGR-Atmospheres.
Rossby waves are planetary-scale waves that naturally occur in the mid-latitudes due to the rotation of Earth. During the summer in the Northern Hemisphere, a wavenumber-five structure contained in the Rossby waves sometimes emerges, and the team believes this wave pattern sets the stage for heatwaves in the US. Wang describes Rossby waves as being like giant meanders in the atmosphere. They are big waves that travel in the atmosphere, way above where airplanes fly. These waves are caused by the rotation of the Earth and differences in temperature between the tropics and the poles. As these planetary-scale waves propagate, they can push and pull the air around them, and move a massive amount of energy, causing changes in the weather on Earth’s surface. When the Rossby waves are slow-moving or stationary, conditions are favorable for extreme weather like heatwaves.
“Our objective was to understand what drives this large-scale pattern that has been statistically related to the events,” says Wang. “We used a simple general circulation model containing only a dry atmosphere in a rotating sphere without complex interactions with moisture or clouds. We modified the model's climatological state of temperature and velocity fields based on the observed thermal structure from the Northern Hemisphere summer. After this modification, we observe a similar wavenumber-five pattern developing days before the heatwave events, resembling the observations. This result suggests that the realistic climatological state provides a critical and conducive environment for the propagation of this specific wave pattern. Since we excluded all the moist processes, it also implies that the dry atmospheric dynamics alone could be sufficient to generate favorable conditions for these extreme events. What does it mean? It means that we found a key ingredient for heatwaves to happen, contributing to the overall understanding of these devastating phenomena.”
Both researchers played key roles in this research. Castañeda ran the simulations and made calculations for obtaining all the figures in the paper. She also structured the manuscript and worked on the writing process. Wang, Castañeda’s advisor, guided the research from the beginning of the project until the publication. He gave constructive feedback during the process and worked on the writing process. They conducted their work in the Weather and Climate Dynamics Laboratory and also relied on Purdue Research Computing to help with calculations.
“Heatwaves have devastating consequences in terms of morbidity and mortality, particularly for economically disadvantaged groups and other vulnerable populations, such as those in outdoor occupations,” says Wang. “Given these profound effects, gaining a deeper understanding of the dynamics behind heatwaves is crucial. This research holds significance because it addresses a critical gap in our forecasting capabilities. By unraveling the complexities of the large-scale pattern that precedes heat extremes by up to 20 days, we have the potential to enhance predictive models on a subseasonal-to-seasonal (S2S) timescale.”
Their research focused on North America, but the team believes that this heatwave prediction model would work for other regions along the midlatitudes. For this to happen, researchers will need to do more research on regional characteristics of the environment enhancing the amplification of the Rossby wave propagation.
“Heatwaves are a concerning issue around the world. For the North Hemisphere, frequent heatwaves also occur along the mid-latitudes,” explains Wang. “For instance, Europe and Russia have experienced increasing severity of heatwaves in recent decades, and some literature has also linked these events with Rossby wave propagation. In the South Hemisphere, regions over South America, specifically Brazil, Argentina and Chile, south of Africa and Australia also experience severe extreme heat events.”
With this finding, the team has identified a critical factor in the occurrence of heatwaves: the climatological state. This research is ongoing and is focused on pinpointing the specific characteristics of this state that are most influential in driving heatwave events. This understanding is pivotal for identifying key variables to prioritize in climate models, potentially leading to significant enhancements in heatwave predictions.
"Our next step is to look at the specific regional disturbances, such as soil moisture conditions, that are contributing the most to the amplification of the Rossby wave pattern and the probability of the events occurring," says Castañeda.
About the Department of Earth, Atmospheric, and Planetary Sciences at Purdue University
The Department of Earth, Atmospheric, and Planetary Sciences (EAPS) combines four of Purdue’s most interdisciplinary programs: Geology & Geophysics, Environmental Sciences, Atmospheric Sciences, and Planetary Sciences. EAPS conducts world-class research, educates undergraduate and graduate students, and provides our college, university, state and country with the information necessary to understand the world and universe around us. Our research is globally recognized, our students are highly valued by graduate schools, employers, and our alumni continue to make significant contributions in academia, industry, and federal and state government.
About Purdue University
Purdue University is a public research institution demonstrating excellence at scale. Ranked among top 10 public universities and with two colleges in the top four in the United States, Purdue discovers and disseminates knowledge with a quality and at a scale second to none. More than 105,000 students study at Purdue across modalities and locations, including nearly 50,000 in person on the West Lafayette campus. Committed to affordability and accessibility, Purdue’s main campus has frozen tuition 13 years in a row. See how Purdue never stops in the persistent pursuit of the next giant leap — including its first comprehensive urban campus in Indianapolis, the new Mitchell E. Daniels, Jr. School of Business, and Purdue Computes — at https://www.purdue.edu/president/strategic-initiatives.
Contributors:
Valentina Castañeda, PhD student with Purdue University’s Department of Earth, Atmospheric, and Planetary Sciences
Lei Wang, assistant professor with Purdue University’s Department of Earth, Atmospheric, and Planetary Sciences
Writer: Cheryl Pierce, Communications Specialist