Earthquake Sensors Hear Hurricanes’ Hidden Turbulence

Hurricanes are so turbulent that the crewed planes that penetrate them to collect data can plummet hundreds of meters with no warning. “Just one downdraft, and then everything went flying,” says Jun Zhang, a hurricane scientist at the University of Miami who flies into the storms with the National Oceanic and Atmospheric Administration (NOAA). He’s recalling a hurricane-hunting flight in 2021 that suddenly plunged about 500 meters. (A typical patch of bad turbulence on a commercial flight won’t drop you more than 30 meters.)

Such aggressive storms literally shake the atmosphere to the point where earthquake sensors can record their signals. That got scientists at Stanford University thinking. Now, research published earlier this month in Science says seismic sensors reveal more detailed data about hurricanes than previously thought. In particular, they uncover information about a hard-to-study part of the hurricane called the boundary layer, which is critical for knowing if a hurricane will intensify.

The hurricane boundary layer is the lowest part of the storm’s atmosphere, typically reaching 1 to 2 kilometers above Earth’s surface. On one hurricane-hunting flight in 2003, Zhang’s advisor flew into the layer, and the plane dove so low that the salty air took out one of the plane’s four engines.

“After that, we won’t really fly into the boundary layer,” says Zhang, who was not involved in the new study. He notes that NOAA scientists still use drones, uncrewed surface vehicles, and parachuted sensors to study this chaotic zone.

The new research could mean one more tool for scientists like Zhang. The Stanford researchers parsed through data from earthquake sensors near the Louisiana coast that happened to be in the path of a 2012 hurricane. These sensors were seismoacoustic, picking up mechanical vibrations in addition to infrasound, which is inaudible to humans. Events like volcanic eruptions emit strong infrasound signals, and the researchers observed that turbulence from the hurricane also emitted such signals. They say this acoustic data could be used to improve knowledge of how the hurricane boundary layer works.

“The boundary layer is really important not just for forecasting in models…but it’s also the most underobserved part of the hurricane,” says atmospheric scientist Ipshita Dey, who worked on the project as a student at Stanford and is now at the National Centre for Atmospheric Science, in the United Kingdom.

How seismic sensors can hear a hurricane

When the 2012 storm, called Hurricane Isaac, made landfall over the network of Louisiana sensors, the wind strength was classified as only a Category 1 compared with the maximum, Category 5. But that doesn’t mean the turbulence wasn’t intense. For what the researchers needed, it “was a really strong event,” says Qing Ji, who also worked on the project as a student at Stanford and is now a postdoctoral researcher at the University of Texas at…