Hurricanes

Hurricanes

Description

Tropical cyclones, hurricanes (or typhoons) are massive storms that form over tropical waters. These intense storms may have wind speeds over 74 mph (119 km/h) to 180+ mph (289+ km/h), varying in strength from Category 1 to 5 on the Saffir-Simpson scale. They generate large waves, producing loud sounds underwater (see What are common underwater sounds). The sounds generated by a hurricane have rarely been recorded by a hydrophone. 

Wind blowing over the ocean generates waves. When these waves become large enough, they break, producing sound under water. Most of the sound of breaking waves is radiated from bubbles trapped under water at the wave’s leading edge. Sound from breaking waves contributes to the background noise in the ocean (see What are common underwater sounds).

Hurricanes (or typhoons) are large storms that form over tropical waters. Hurricanes have wind speeds of 74 mph (119 km/h) to 180+ mph (289+ km/h). Waves can be very large in a hurricane, generating a loud sound underwater that can be heard in the local region. The sounds generated by a hurricane have rarely been recorded by a hydrophone.

Hurricane Gert 1999

Hurricane Gert was a 1999 storm that did not make landfall but caused damage in Bermuda from high winds. Hurricane Gert passed almost right over a NOAA hydrophone deployed at a depth of 800m that was monitoring the Mid-Ocean Ridge for earthquakes.

Track of Hurricane Gert in 1999. NOAA hydrophone location is indicated by the white dot. Gert was a Category 4 hurricane as it passed the NOAA hydrophone. Image from NOAA.

Gert was a strengthening category 4 hurricane with winds of 126-150 mph (202km/h to 241km/h) as it passed the hydrophone on September 15th. The recording from that hydrophone illustrates that even at very high winds speeds there is a positive relationship between wind speed and the underwater sound levels generated by a hurricane. The sound pattern is similar to a cross section of the wind in a hurricane.

Underwater acoustic intensity level L = 10 log(I/ Watt/m2), in the 10 to 50 Hz band, received by the NOAA hydrophone on 15 September, with 5 minute averaging. The maxima at 13:30 and 15:30 GMT correspond to the powerful winds of the hurricane’s eye-wall, and the minimum at 14:30 GMT corresponds to the hurricane’s eye. The sound pattern is similar to a cross section of the wind in a hurricane. Modified from Figure 1 in Wilson, J. D., & Makris, N. C. (2008). Quantifying hurricane destructive power, wind speed, and air-sea material exchange with natural undersea sound. Geophysical Research Letters, 35(10).

Hurricane Irma September 2017

Hurricane Irma was a powerful category 5 hurricane that made several landfalls in the Caribbean and Florida in September 2017, causing catastrophic damage in many areas. Hurricane Irma made landfall at Marco Island, FL and then Naples, FL on September 10, 2017 as a category 3 storm with 115 mph (185 km/h) winds. Irma then travelled up the Florida peninsula, passing inland of Sarasota, FL. Hurricane Irma brought peak winds of around 75 mph to the Sarasota area where a hydrophone near shore recorded underwater sounds made by the hurricane winds. The hurricane related underwater sound levels increased 30dB at the peak of the onshore winds in the Sarasota, FL area.

Sound levels recorded by a hydrophone at New Pass, FL (near Sarasota) during the passage of hurricane Irma in September 2017. Image curtesy David Mann, Loggerhead Instruments.

The hurricane passed directly over the Florida Keys National Marine Sanctuary as a Category 4. Using passive acoustic data collected from bottom-mounted hydrophones, scientists studied the impacts of Hurricane Irma on the acoustic environment at two coral reef sites within the Florida Keys (Simmons et al., 2021): Western Dry Rocks (before and during the storm) and Eastern Sambo (before, during and after the storm). During the peak of the hurricane, the low frequency component of the underwater sound was impacted the greatest; the sound level increased by 40–50 dB over pre-storm levels in the ~10–100 Hz frequency range.

The scientists were able to determine that, as the hurricane passed, the cumulative sound exposure level (cSEL) near the seabed was comparable to the cSEL of a small vessel operating continuously at these sites for 1–2 weeks.

Hurricanes Florence 2018, Dorian 2019, and Humberto 2019

The Atlantic Deepwater Ecosystem Observatory Network is comprised of passive acoustic sensors mounted on bottom landers at seven locations on the U.S. Mid- and South Atlantic Outer Continental Shelf. Two years of data from the Network were used to study the acoustic impact of three hurricanes on underwater sound (Tripathy et al., 2021). The hurricanes had different strengths as they passed over the landers (Table 1). The scientists focused their analysis on several frequency bands, including 10-100 Hz, 100-1000 Hz, and 0.1-4.0 kHz. Little increase in the mean sound level was found in the 10-100 Hz band, “as hurricanes typically increase the ambient sound level at frequencies greater than 100 Hz” (Tripathy et al., 2021). Significant increases in the ambient sound level were found in the 0.1-4.0 kHz band. In analyzing the acoustic data, the scientists found that the hurricanes resulted in an increase in sound level during the passage of all three hurricanes.

Atlantic Deepwater Ecosystem Observatory Network (ADEON) (https://adeon.unh.edu/landers)

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