There were all the ingredients to captivate the audience: an airship, a scientific expedition to the North Pole, an unforeseen disturbance, an unfortunate accident and the struggle for survival of the survivors clinging to life in their tent, the only and last human outpost among the boundless expanses of arctic ice. And yet, the story of the airship Italia was not the imaginative fruit of some pen passionate about thrillers. That of the airship Italia was a story that first shocked and then enthralled generations of Italians: not only those who, at the beginning of the last century, experienced first-hand - thanks to the work of journalists who rushed to the scene - the uncertainty about the fate of the crew of the expedition led by Umberto Nobile; but also those who, in the following decades, have turned to science to try to give an answer to the many questions left open by the mysterious shipwreck.
It was May 6, 1928 when Italy, captained by General Nobile, accompanied by the support ship Città di Milano, and with a crew of 16 men on board, including technicians and scientists plus the fox terrier Titina, the expedition's mascot, reached the bay of King Ny-Ålesund in the Svalbard Islands. Objective of the mission, to explore as many unknown regions as possible of the Arctic continent and, above all, to reach the North Pole. After a series of preparatory flights, on 23 May the airship departed for the Polo, where it will arrive almost 20 hours later, on 24 May. Here the crew runs into a violent disturbance that prevents them from descending on the icy surface, so they set off again in the direction of the base in Svalbard but have to deal with a progressive worsening of the atmospheric conditions. After 24 hours of flight, the airship finds itself immersed in a very thick fog with a stormy wind in the bow, with still half the way to go and the ice blocking the rudder mechanism. At 10.33 in the morning the stern of the Italia and the command gondola hit the frozen ground about 100 kilometers from the Svalbard Islands, throwing 10 men to the ground and leaving 6 others trapped on board. The shell of the airship regains altitude and disappears from view never to be found again, while the survivors are carried adrift by the ice towards Foyn and Broch Islands and take refuge in a tent still remembered today as the "Red Tent", colored red with fuchsin to be more visible to rescuers . Although pilots and explorers from many countries are mobilized for the rescue, 49 days pass before the survivors are identified and finally rescued. The biggest mystery, however, immediately appears what surrounds the SOS messages launched by the survivors: the requests for help, in fact, fail to reach the Città di Milano ship anchored in the Svalbard Islands, but are incredibly picked up by a young Russian radio amateur 1.900 kilometers away from the Red Tent.
Last year, 90 years after the accident, a study by the National Institute of Geophysics and Volcanology (INGV) reconstructed the space weather conditions (i.e. the ionospheric conditions, solar physics and geomagnetism) at the time of the shipwreck, to attempt to explain the problems encountered in radio communications. These enormous difficulties, and in particular the late reception of the SOS launched by the survivors, have generated an enormous amount of discussion and controversy described, throughout the decades of the last century, in memorials, newspaper articles and judicial trials. Bruno Zolesi, INGV researcher who took care of the research tells us about this adventure.
Let's start outlining the scientific framework… What is meant by space weather?
The term "meteorology" generally refers to the science that studies the physical phenomena responsible for the weather, such as rain, wind, clouds and the measurable variables related to them such as temperature, humidity and pressure of the air. Space weather, on the other hand, studies and tries to predict those phenomena that occur on the Sun, in the solar wind, in the magnetosphere and in the ionosphere that can have effects on human life and on technological systems on the ground and in space.
What is the ionosphere instead?
The term ionosphere indicates that part of the earth's atmosphere in which the density of ions and electrons reaches physically relevant values, ie such as to influence the refractive index and the reflection of radio waves in the HF band (3MHz-30MHz). This portion of the atmosphere is located above 50 km from the earth's surface.
Going back to the story of the airship Italia, what does the study with which INGV was able to reconstruct the causes of the delays in rescuing the survivors consist of?
This is a study published last year with which, thanks to the application of recent geophysical models and the analysis of an enormous quantity of observations in polar areas made in the last century, it was possible to confirm some hypotheses on the gray area around the transmitting apparatus of the Red Tent. The disturbed conditions of the ionosphere and magnetosphere of that period then served to formulate other theories on the complex story of radio communications between the shipwrecked and the ship Città di Milano. These hypotheses had already been put forward by radio propagation experts of the time: what was missing, and which the INGV study provided, was an official confirmation based on scientific evidence not yet available at the material time.
What were the results and what consequences did they have on the reconstruction of the accident?
The maps of the HF radio propagation parameters and of the minimum distance reached by a certain radio frequency clearly demonstrated that the 9.4 MHz radio frequency (that is, the one used by the shipwrecked) could not, even in undisturbed ionospheric conditions, be heard from the support vessel Città di Milan. In fact, the gray area for that frequency widely covered the whole area of the Svalbard Islands, where the ship was moored, up to the northernmost part of Europe. Furthermore, the analysis of geomagnetic observations obtained at the time in areas close to the polar ones highlighted a magnetic storm in progress during the first days of the shipwreck. The peculiar behavior of the ionosphere in arctic areas was instead obtained from the geophysical models elaborated in the last decades of the last century. In the XNUMXs, in fact, exploration, and therefore also the continuous and systematic observation of the ionosphere through vertical radiosondes, was still in its infancy. Knowledge of the blind spot was therefore based only on the experience of a large amount of radio links made at low and mid latitudes by military and civilian users, including radio amateurs.
What was the most emotionally engaging aspect of having given an answer to an “unresolved” question for so long?
As we have already said, the geophysical causes that generated the radio communication difficulties in the Red Tent affair were well known to the technical experts of the Regia Marina. However, this study, using recent geophysical models and a consolidated theory of ionospheric radiopropagation, confirmed the intuitions a posteriori and tried to give a definitive answer to those questions that had not yet been completely clarified until a year ago. This work therefore brings with it the "satisfaction" of having made virtuous use of ionospheric models to "solve" an important historical event, rather than to predict the geophysical conditions of the future. We could define it as a study of the paleoionosphere, in addition to the already existing and fascinating branches of paleomagnetism and paleoclimatology.
How much interest did the story of the airship Italia arouse at the time?
In the XNUMXth and XNUMXth centuries, due to the romantic and adventurous ideals with which their protagonists were invested, geographical explorations aroused great interest both among the public and, naturally, among insiders and members of the main national geographical societies shipping organizers. To this enormous interest, comparable to what we have today for space expeditions, was added, in the case of the adventure of Italy, also the technological competition between flying machines and the fascination that the practice of flight aroused in those times . A decidedly not secondary aspect was then that linked to what we would today define as "gossip": in fact, despite the often dramatic implications of these expeditions, the newspapers and memorials were punctually populated with events, curiosities, controversies and mysteries exactly like those that still accompany today any large company.
Could something similar happen today, almost a century after the shipwreck?
Well, I would say no: today, thanks to the results achieved by technological progress, such an event could hardly occur. Those who venture into extreme geographical areas such as oceans, deserts or polar areas, or far from inhabited areas, have in fact available portable satellite telephone systems which nowadays are able to cover even those areas of the planet. However, those who continue to use radio waves in the HF band for long-distance connections, which are still precious - especially in emergency situations - due to their ease of use and low cost, must continue to take account of the gray area and of the variability of the reflective layer of the ionosphere. It should also be remembered that even in 1928 the crew of the airship Italia had thoughtfully thought of an additional radio link system: a long-wave transmitter, unfortunately lost in the shipwreck.
Graphic - Isolines of the edge of the shadow zone for each radio frequency around the Red Tent. The red line underlines the isoline of the 9.4MHz radio frequency, the one used by the survivors of the dirigible Italy