A heat dome weather event affecting millions in the US midwest and east coast in July 2024 triggered unusual communications disruptions due to tropospheric ducting, a phenomenon where high temperatures allow radio, TV, and microwave signals to travel hundreds of miles beyond their normal range.
False alarm in Indiana
In Huntington County, Indiana, an outdoor emergency siren activated on July 1 at 3 a.m. without any storm or tornado warning. Thomas Fuller, the county's deputy director for emergency management, said the siren was triggered by radio signals originating 300 miles away in Iowa that accidentally matched the activation code. “When there’s an activation, it’s usually by the Huntington county dispatch center. But this siren activated all by itself due to the radio signals all the way from Iowa,” Fuller said.
Tropospheric ducting explained
Tropospheric ducting, also known as tropospheric propagation, creates atmospheric tunnels that guide radio waves over long distances. Kyle Spillane, a member of the Mid-MO Amateur Radio Club, explained: “Tropospheric ducting is basically little tunnels in the sky that the radio waves bounce through until they eventually come out. The big factors are temperature, air pressure and humidity.” This can cause radio, TV, and even 5G cellphone signals to interfere with systems far away.
Impact on communications
In Ohio, drivers reported their car radios picking up stations from hundreds of miles away or losing coverage entirely. The phenomenon also affects over-the-air TV, radar, pacemakers, internet routers, satellites, and cellphones, especially 5G devices using higher frequencies. Spillane noted that “the higher the frequency goes, the more likely it is to be affected by tropospheric ducting.”
Climate change connection
Researchers predict more frequent and extreme heat domes due to climate change. A 2023 study found that human-caused climate change increases the probability of extreme heatwaves in the Pacific Northwest by at least 150 times. The 2021 heat dome in that region caused an estimated 1,200 deaths in Washington, Oregon, and British Columbia. As heat domes become more common, tropospheric ducting-related interference may increase.
Emergency services concerns
Despite these risks, the US Forest Service stated that its firefighters experience little impact from heat on radio systems due to equipment design. However, Fuller and other emergency workers worry about “alert fatigue” from false alarms. Huntington County has two manual ways to shut off sirens, but repeated false alarms could make the public less responsive. “We’re always concerned about alert fatigue,” Fuller said. “It’s happened a couple of times, three or four years ago, where we get these signals from different places.”
