The devastation caused by the bombing raids during the Second World War has been immortalized in countless images. The impacts on cities and on the environment are still found today. Now, researchers have discovered that the effect of these raids was felt all the way into the higher layer of the atmosphere, past the edge of space.

As reported in Annales Geophysicae, the team used data collected by the Radio Research Centre in the UK between 1943 and 1945. They studied the conditions of the ionosphere, the portion of Earth’s atmosphere between 60 and 1,000 kilometers (37 and 620 miles) above the planet's surface, by sending radio pulses 100 to 300 kilometers (62 to 186 miles) into the sky.

The team matched these observations to the time 152 large Allied air raids took place in Europe and found a lower concentration of electrons in the ionosphere. The researchers believe that the shockwaves were powerful enough to heat up the upper atmosphere, leading to a reduction of ions.  

"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," Professor Chris Scott, from the University of Reading, said in a statement. "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."

Understanding the ionosphere is very important since it is key to modern technologies, such as long-distance communication, GPS, and radio telescopes. Its strength is influenced by solar activity and our planet’s magnetic field, but the changes in the observations suggest it's influenced by a lot more than our models currently take into account.

While widespread air raids are fortunately a thing of the past, data from them can help us understand the interplay between events near the planet's surface and the highest layer of the atmosphere.

"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," Professor Patrick Major, University of Reading historian and a co-author of the study, added.

The team is planning a citizen science project to digitize early atmospheric data. This will be particularly interesting in terms of smaller air raids as it might give an indication of the minimum explosive energy necessary to make a detectable change in the ionosphere.