In May 1928, a team of explorers returning from the North Pole via airship crashed on the frigid ice. Their attempts to use their portable radio transmitter to call for help failed; although they could hear broadcasts from Rome detailing attempts to rescue them, their calls could not reach a relatively nearby ship. Now, new research suggests that the communication problems may have been caused by radio “dead zones,” made worse by high solar activity that triggered massive solar storms.
High frequency radios bounce signals through the ionosphere, the upper layers of Earth’s atmosphere most affected by solar radiation. Around the poles, the ionosphere is especially challenging for radio waves to travel through—a fact not yet realized in the 1920s when scientists were just beginning to understand their movement through the charged air.
"The peculiar morphology of the high latitude ionosphere, with the large variation of the electron density…may cause frequent problems to radio communication," says Bruno Zolesi, a researcher at the Istituto Nazionale di Geofisica e Vulcanologia in Rome. Zolesi, who studies how the Earth’s atmosphere reacts to particles emitted by the sun, is lead author of a new study probing the tragedy of the airship Italia. He and his colleagues modeled the radio environment of the North Pole at the time of the expedition. They found that space weather, which is the way that charged particles from the sun can affect the environment around planets, likely plagued the expedition, delaying the rescue of the explorers by more than a week and perhaps costing the life of at least one of the team members.
“The space weather conditions are particularly intense in polar regions,” Zolesi says.
The ‘Red Tent’
On 24 May 1928, after just over 20 hours of flight, the ‘Dirigible Italia,’ captained by Italian designer Umberto Nobile, circled the North Pole. Nobile had flown on a 1926 Norwegian expedition aboard an airship he had designed; that was the first vehicle to reach the North Pole. Two years later, he had returned to stake a claim for his native country.
After a brief ceremony at the pole, with winds too strong to attempt a landing on the ice, the vehicle turned south to make the 360-kilometer return trip to the crew’s base on the Svalbard archipelago. But an unknown problem caused the airship to plunge to the Earth, slamming into the ice and shattering the cabin. The crash killed one of the explorers. The balloon, freed from the weight of the carriage, took to the air, carrying six more crew members away, never to be seen again. The nine survivors sheltered beneath a red tent that gave its name to the historical disaster.
Among the supplies left on the ice was the simple high-frequency radio transmitter intended to allow communications between the airship and explorers on the ground. The low-powered radio ran on batteries and had a transmission range of 30 to 50 meters.
As the shipwrecked crew settled into their uncomfortable new quarters, radio operator Giuseppe Biagi began sending SOS messages. At the 55th minute of each odd hour, the prearranged time for the Italia to contact the Italian Navy’s ship, Citta dei Milano, anchored in King’s Bay, he pled for help, then listened in vain for a response.
Amazingly, while the tiny antenna could not contact the ship, it could pick up radio broadcasts from Rome—with signals originating more than ten times farther away than the point where the navy ship was docked. The explorers listened as news of their disappearance and updates on the rescue operations were broadcast.
It took nine days for someone to finally hear their calls for help. On 3 June 1928, a Russian amateur radio enthusiast, Nicolaj Schmidt, picked up the SOS with his homemade radio receiver in a small village approximately 1900 km from the Red Tent. After nearly 50 days on the ice, the explorers were ultimately rescued, though 15 of the rescuers died in the attempt.
Over the past 90 years, the crew of the Italia have been the subject of several books and articles, as well as a 1969 Soviet-Italian move starring actor Sean Connery. The continued cultural interest over the event intrigued Zolesi and his colleagues; they hoped to combine their scientific knowledge with cultural history to explain some of the radio communication problems encountered by the survivors.
Along with exploring previously untapped regions of Earth, the first half of the twentieth century was marked by the exploration and investigation of Earth’s ionosphere. Systematic measurements of radio and telegraph transmissions provided the first realistic picture of the ionosphere and a generalized understanding of how radio waves move through charged regions. But in 1928, scientists were only beginning to understand the ionosphere and the space weather that affected how radio waves traveled.
Radio waves sent through the ionosphere travel upward at an angle, and the triangular wedge beneath their source and the point where they return to ground is known as their skip distance. Inside that area exists a dead zone wherein their signal cannot pass (with the exception of the limited ground reach they also cover). Dead zones, as we now know, vary based on the strength of the broadcast signal and the conditions of the ionosphere.
Zolesi and his colleagues relied on a standard international model of the ionosphere to provide a monthly average picture of the northern pole. But their lack of knowledge about the Earth’s atmosphere nearly proved fatal to the team. The 8.9 MHZ frequency relied on by the explorers would have fallen in the radio dead zone for locations to the north of the 66° N line of latitude. Both the Red Tent and the Citta di Milano sat at nearly 80° N, while Arkhangelsk, the closest city to Schmidt, sits at 64.5°.
The researchers also studied sunspot drawings captured by the Mount Wilson Observatory in California between 25 and 31 May 1928. They revealed a significant increase in the number of sunspot groups. Sunspots have been directly linked to increased solar radiation and electron density in the atmosphere, making them an important marker of the ionosphere’s behavior. The researchers also examined the history of two magnetic observatories in England and Scotland to understand how Earth’s geomagnetic field could have played a role. They found that the planet underwent periods of magnetic fluctuations in mid- to late May 1928, peaking on 28 May.
“The space weather conditions were affected by a significant geomagnetic storm during the early days after the shipwreck,” Zolesi says. “These conditions might have severely affected the radio communications of the survivors during the tragedy.”
The researchers concluded that it may have been impossible for the stranded team to reach the Citta di Milano with their low-powered radio, particularly given their unstable antenna and the noisy radio environment courtesy of the local coal mining industry and news agencies. The addition of skip distance issues and space weather conditions not fully understood at the time made communication an even greater challenge.
As the researchers explained in their paper, which was published in the journal Space Weather, the increased activity of the sun should have released more charged particles, which would have interacted with the layers of the upper atmosphere, especially around the northern and southern poles they are funneled to by the planet’
The lessons learned by the tragic Italia expedition could be particularly relevant as humans move to off-planet exploration. While space weather didn’t play a direct role in the airship’s crash, it played a crucial role in sabotaging calls for help and the belated rescue attempt. Similar problems could plague expeditions to other bodies in the solar system if the effects of space weather aren’t considered.
“For the moon and Mars, the problems could be completely different because there are different ways radio communication may be used,” Zolesi says. “But many other problems may occur due to the large number of space weather events [affecting those].”