Confronting the eye of the storm

The day Kristen Corbosiero started her postdoctoral training at the National Center for Atmospheric Research in Colorado, Hurricane Katrina hit New Orleans.

While the tragedy that ensued heightened awareness about the dangers of hurricanes and the importance of the science behind forecasting them, Corbosiero was already on the case, having studied weather systems — especially tropical cyclones, or hurricanes — as a graduate student.

“As one of my advisors once told me, ‘If it’s in the atmosphere and it’s rotating, I’m interested in it,’ ” she said.

Corbosiero, who grew up outside of Boston, traces her fascination in weather back to middle school, when she joined a “weather club” directed by a geography teacher.

“We met before school every morning to draw weather maps and discuss what was going on,” Corbosiero said, “and we got to deliver forecasts in the morning announcements.”

As an assistant professor in the Department of Atmospheric and Oceanic Sciences at UCLA, Corbosiero continues to analyze weather patterns, although these days at a much more sophisticated level. She studies a variety of phenomena, including tracking and forecasting of lightning and thunderstorms, but her primary focus is on hurricanes—and in particular, how the physical structure of these massive storms is related to changes in their strength.

“One of the biggest questions concerning hurricanes is how they intensify,” Corbosiero said. “I’m interested in what we can learn about intensity from the shape of the eye wall.”

To get those answers, Corbosiero uses data taken from actual observations of hurricanes as well as numerical modeling that simulates their structure. The observations come from radar and satellite monitoring when hurricanes venture close enough to the U.S. coast, and from a fleet of Air Force and government planes that fly into hurricanes over the open seas and use special equipment to measure their properties.

Armed with that information, Corbosiero looks to document the hurricane’s structure at each point of its intensity. Among her questions: Does the hurricane have a clear eye?

What is the shape of the eye wall — the ring of intense thunderstorms and winds that surround the eye?

“The hurricane eye wall can be circular, but it can also take on interesting shapes,” Corbosiero said. “We want to know the physical phenomena that cause the hurricane eye wall to take on these unusual forms, and how these forms are related to the storm intensity.”

In her effort to address that issue, Corbosiero also studies the activities of rain bands—the thunderstorms that form outside the eye wall.

“All of the energy for the storm comes from air flowing into the center. You can imagine that if a rain band is outside the eye wall, it might take some of the energy from it. Understanding how the rain bands affect the eye wall and what causes them to be where they are can give us additional insights.”

But sending an airplane through a hurricane has its limitations, most notably the inability to obtain data at all points of the storm simultaneously. So Corbosiero also uses numerical modeling to simulate the form taken by all of the hurricane’s quadrants at all times as a way of gleaning a clearer picture of the continuous evolution of the storm.

For her doctoral research, Corbosiero capitalized on some of the most complete radar and aircraft reconnaissance data sets ever recorded of a tropical cyclone in her analysis of peculiar aspects of Hurricane Elena in 1985 — a storm that took an unusual, looping path through the Gulf of Mexico before hitting the U.S. Gulf Coast. From these observations, she was able to document what the numerical models had suggested: that rain bands outside the core of tropical cyclones have the properties of a type of wave.

Corbosiero also uses the observational data to improve numerical models. In her simulations of Hurricane Katrina, Corbosiero found a triangular eye wall — something that isn’t seen in observations of Katrina or other hurricanes; eye walls are typically squares or ellipses.

“That told us that even though we have this powerful, state-of-the-art model, it needs to be improved,” she said. “We’re not matching the structure with what we see in nature.”

While there were major shortcomings in the preparedness for Hurricane Katrina and the response that followed, the forecast for the storm was quite accurate. Not so for Hurricane Rita, which made it to the Gulf Coast less than a month later. After predictions that Rita would hit Houston led to widespread evacuation, the storm completely missed the city, landing significantly further east.

Last year, Hurricane Dolly rapidly intensified to Category 2 status on July 23—something none of the models had predicted only hours before it occurred — before hitting southern Texas. These and other examples illustrate that there is still work to do when it comes to forecasting the path and intensity of hurricanes.

Corbosiero is looking at how to better track hurricanes as well, but her primary interest, predicting intensity, is even more challenging.

“The direction of the storm is dictated by larger-scale features in the environment, whereas the intensity is controlled by more subtle, smaller-scale features,” she said.

In the wake of the publicity surrounding Katrina and Rita, Corbosiero has more company in endeavors, with many new researchers joining the field. She remains as intrigued by weather patterns as she was in her middle school weather club — but, given the persistent threats to the public from hurricanes, her scientific curiosity is also based on a sense of higher purpose.

“By identifying the causes of intensity changes, we hope to be able to make more accurate forecasts so that we can get people out of harm’s way,” Corbosiero said. “It gives me great satisfaction to be able to use this basic research toward a practical end.”

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This story is reprinted courtesy of the UCLA College Report.