- Atmospheric sciences professor Stephen Nesbitt, left, and graduate student Daniel Harnos analyzed passive microwave satellite data to identify telltale structural rings in tropical storms that are about to intensify into hurricanes. Photo courtesy Univ. of Illinois/L. Brian Stauffer
NASA’s Hurricane Science Research Program has supported new work that uses satellite data to spot ahead-of-time indicators of hurricanes.
Satellite imagery most commonly used for meteorology only looks at the clouds at the top of the storms. But that yields little insight as to what’s going on inside the system, specifically processes that whip up, intensify, even steer the direction of storms.
But thanks to the efforts of atmospheric sciences professor Stephen Nesbitt and graduate student Daniel Harnos at the University of Illinois in Champaign, they have identified telltale structural rings in tropical storms that are about to intensify into hurricanes.
Microwave monitoring
Their research is focused on passive microwave satellite imagery, demonstrating how to use existing satellites to monitor tropical storm dynamics and predict sudden surges in strength.
“What makes it ideal for what we are doing is that it’s transparent to clouds. It senses the amount of ice within the clouds, which tells us the strength of convection or the overturn of the atmosphere within the hurricane,” Nesbitt said. “It’s somewhat like trying to diagnose somebody with a broken arm by taking a picture of the arm, versus being able to X-ray it,” he noted in a just-issued university press release.
The researchers sifted through data from passive microwave satellites from 1987 to 2008 to see how hurricanes behaved in the 24 hours before a storm underwent rapid intensification.
What did they find?
The researchers found a consistent pattern – low-shear storm systems shaped a symmetrical ring of thunderstorms around the center of the system about six hours before intensification began.
Furthermore, as the system strengthened into a hurricane, the thunderstorms deepened and the ring became even more well-defined.
“Now we have an observational tool…that can set off a red flag for forecasters,” Nesbitt said. By sighting a convective ring feature, there’s a high probability that a storm may undergo rapid intensification, he added.
Since passive microwave satellites orbit every three to six hours, meteorologists can use them to track tropical storms and watch for the telltale rings to give forecasters about a 30-hour window before a storm hits its maximum strength.
The team has published their findings in the journal Geophysical Research Letters.
Next steps
As a next step, researchers hope to even further increase their forecasting ability by modeling the internal dynamics of the storm systems as they intensify to pinpoint the causes of the structural changes they observed and find out what drives the intensification process.
“The satellite gives up as snapshot of what’s taking place,” Harnos explained. “We know what’s going on, but not how those changes are occurring to end up in the pattern that we’re seeing.
The team is now set on computer modeling of hurricanes — both real storms and idealized storms — to see dynamically, structurally, what’s taking place and what changes are occurring to produce the patterns that they see in the satellite data.
“It’s a really critical piece of information that’s really going to help society in coastal areas, not only in the U.S., but also globally,” said Nesbitt.
By Leonard David