Hello from the outside: heat domes impeding radio and other signals in US midwest

Higher temperatures can cause radio, TV and microwave signals to travel hundreds of miles farther, upsetting communications

It was 3am in north-east Indiana’s Huntington county when the outdoor emergency alarm went off on 1 July.

The only issue? There wasn’t a storm, tornado or any other emergency weather event forecast or present anywhere for hundreds of miles.

“It happened right in the middle of the night. I woke up at around 5am and saw on our Facebook page multiple comments [of people writing], ‘Hey, our siren went off last night.’ I thought, ‘That’s weird,’” recalled Thomas Fuller, Huntington county’s deputy director for emergency management.

“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.”

Amid the heat dome weather event that affected hundreds of millions of people in the midwest and on the east coast this month, strange and little-observed communications interruptions have started to unfold.

The emergency alarm in Huntington county received radio signals from 300 miles west that accidentally matched the activation code for the siren, said Fuller.

In Ohio, residents driving in their cars, their radios tuned to the local news and music, were warned that they could find themselves abruptly listening to radio stations hundreds of miles away, or their coverage simply blanked out.

These events are down to the high temperature’s effects on tropospheric ducting , the atmospheric weather phenomenon that can facilitate radio, television and microwave signals traveling for hundreds of miles. The ducting, also known as tropospheric propagation, typically lasts anywhere between minutes to several hours, but sometimes longer, depending on the weather and atmospheric conditions in a particular location.

Radio is an essential mode of communication during emergency situations, when internet and cell coverage regularly falters, but is also an everyday tool for thousands of forest firefighters, railroad workers and the maritime industry around the Great Lakes region at this time of year.

“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 in the air all [which] control how big these ducts are,” says Kyle Spillane, who lives in Jefferson City, Missouri, and is a member of the Mid-MO Amateur Radio Club.

It can also affect over-the-air television programming.

“The problem is, if a tropospheric duct were to appear between two areas with different TV stations, the signals from the TV stations could get in there, travel through the duct and basically come out with no real loss in a different TV market,” Spillane continued.

With researchers predicting more frequent and more extreme heat domes – a weather pattern in which a high-pressure system in the upper atmosphere stalls over a large area, trapping hot, humid air close to the ground – for high population regions such as North America, Europe and beyond – the consequences for communications systems may be significant.

Climate change could also play a role in a potential growth in communications interference resulting from tropospheric ducting.

A 2023 study found that the Pacific north-west – a region where radio communications are vital to forestry and other emergency responders – is expected to experience more “heat-dome-like circulation” and concluded that “human-caused climate change increases the probability of extreme heatwave by at least 150 times”. In June and July 2021, an historic heat dome resulted in an estimated 1,200 deaths in Washington state, Oregon and British Columbia.

What’s more, the risk of interruption from tropospheric ducting isn’t limited to radio and television signals: radar, pacemakers, internet routers, satellites and cell phones use radio-frequency energy to transmit information.

“Your cellphone is a radio; it just operates on a higher frequency, and the higher the frequency goes, the more likely it is to be affected by tropospheric ducting,” says Spillane.

Cellphones that use 5G capability are especially affected as they use a higher radio wave frequency.

Still, some experts say that emergency services organizations typically have multiple ways to communicate during times of intense need.

“Based on the equipment we use and how our radio systems are designed, Forest Service firefighters experience little to no impact to radio systems due to heat,” says a spokesperson for US Forest Service. The spokesperson did not specifically respond to a Guardian question asking about any links between tropospheric ducting and potential radio communications interruption.

For amateur radio enthusiasts such as Spillane, tropospheric ducting can, in fact, allow for communication with people hundreds of miles away via an inexpensive radio system, rather than only with radio users located nearby.

“[Heat domes fueling tropospheric ducting] is certainly another aspect of climate change that people need to consider, but I think there are much more important aspects of climate change to look at,” he adds.

Fuller, in Huntington county said that there are two additional, manual ways to shut off outdoor emergency sirens if they are accidentally activated.

“If you’re outside and you hear that siren, you’re supposed to seek shelter and additional information. The siren system is not to tell you what’s happening,” he says.

But he and other emergency service workers are concerned about the public potentially getting lax about their safety due to false alarms, something that could be compounded by climate-related radio interference. A series of false warning alarms at a community in Washington state downstream of a major dam has roiled local residents in recent years, forcing the alarms to be turned off.

“We’re always concerned about alert fatigue,” said Fuller. “It’s happened a couple of times, three or four years ago, where we get these signals from different places.”