The Second World War brought unprecedented destruction upon the face of the Earth — one that reached up to the edge of space, new research reveals.

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Allied bombing raids during the Second World War caused shockwaves so strong that they weakened the ionosphere, the electrified layer of the atmosphere that reaches up to 1000 km (621 mi) above ground, reports a new paper from the University of Reading.

High-altitude bombing

“The images of neighbourhoods across Europe reduced to rubble due to wartime air raids are a lasting reminder of the destruction that can be caused by man-made explosions,” says Chris Scott, Professor of Space and Atmospheric Physics at Reading and one of the paper’s coauthors. “But the impact of these bombs way up in the Earth’s atmosphere has never been realised until now.”

“It is astonishing to see how the ripples caused by man-made explosions can affect the edge of space. Each raid released the energy of at least 300 lightning strikes. The sheer power involved has allowed us to quantify how events on the Earth’s surface can also affect the ionosphere.”

World War Two was perhaps the single most calamitous war humanity has ever embarked upon. Fueled by an already-ripened Industrial Revolution and incredible technological leaps, belligerent countries unleashed unprecedented destruction upon their foes’ troops and homelands.

So awesome was their fury that not even the ionosphere escaped unscathed. The team drew on daily records collected by the Radio Research Center in Sough, UK, between 1943-45, a period that saw rapid development of radio and radio-based technology (such as radar). Among other research topics, scientists at the center shot sequences of shortwave radio pulses at heights between 100 and 300 km (62 to 186 mi) above the Earth’s surface in order to better understand the height and ionization levels of layers within the upper atmosphere.

Their work helped reveal the existence of the ionosphere — and now, it’s helping researchers understand how natural forces from below, like lightning, volcanic eruptions, or earthquakes, affect this layer of our atmosphere.

The ionosphere underpins several technologies such as radio communications, GPS systems, radio telescopes, and some variations of radar, as it helps bounce radio signals back down towards the surface (instead of letting them escape to outer space). So it’s not hard to see why we want to have as comprehensive an understanding of it as possible. Being a highly-charged layer, the ionosphere is strongly influenced by solar activity.

However, scientific modeling has revealed that our star alone cannot account for all the waxing and waning we see in this layer. Ground-level activity has to account for the rest.

Higher-altitude effects

To help us understand how ground-level events influence this layer, the team studied the ionosphere’s response around the time of 152 large Allied air raids in Europe.

The team focused on Allied bombing runs over continental Europe rather than attacks more close to the center — such as the infamous London ‘Blitz’ — due to their more sporadic nature. The Blitz was a monumental and sustained bombing effort, but its continuous nature (and the fact that relatively little information is available to accurately time and locate individual runs) made it much more difficult for the team to tease out its effects from natural, seasonal variations in the ionosphere. In other words, Nazi Germany dropped so many bombs on Britain and for so long, that it ruined the data sample.

Another factor that made the team focus on Allied raids was sheer ‘boom’. The German Luftwaffe employed two-engine tactical bombers, which carried relatively small bombs; the Allies, in contrast, relied on four-engine strategic bombers that carried much larger ordinance — such as the 10-tonne ‘earthquake bomb’ Grand Slam. Quantity, it turns out, truly is a quality in and of itself:

“Aircrew involved in the raids reported having their aircraft damaged by the bomb shockwaves, despite being above the recommended height,” says Professor Patrick Major, University of Reading historian and a co-author of the study. “Residents under the bombs would routinely recall being thrown through the air by the pressure waves of air mines exploding, and window casements and doors would be blown off their hinges.”

“There were even rumours that wrapping wet towels around the face might save those in shelters from having their lungs collapsed by blast waves, which would leave victims otherwise externally untouched.”

The team reports that electron concentration in the ionosphere dropped significantly following these events, due to shockwaves generated by air-detonating bombs exploding near the surface. These pressure waves, the team believes, heated up the upper atmosphere, enhancing the loss of ionization.

“The unprecedented power of these attacks has proved useful for scientists to gauge the impact such events can have hundreds of kilometres above the Earth, in addition to the devastation they caused on the ground.”

The researchers now need members of the public to help digitize more early atmospheric data, to understand the impact of the many hundreds of smaller bombing raids during the war, and help determine the minimum explosive energy required to trigger a detectable response in the ionosphere.

The paper has been published in the journal Annales Geophysicae.