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The effects of bombing raids during the Second World War can still be seen in the Earth's atmosphere.
The researchers revealed that the shock waves produced by aerial attacks on European cities more than 70 years ago were large enough to weaken the ionosphere about 620 miles above the UK.
The results, published in the journal European Geosciences Union (EGU) Annals Geophysicae, could help scientists understand how natural forces on Earth – lightning, volcanic eruptions, earthquakes – affect the atmosphere above the Earth.
"The images of small neighborhoods in Europe following wartime airstrikes are a lasting reminder of the destruction caused by man-made explosions," said Chris Scott, professor of space and atmospheric physics at the University of Toronto. University Reading, said in a statement.
Surprisingly, the impact of these bombs "in the Earth's atmosphere", he said, has not yet been realized.
Researchers at the British University analyzed daily records collected between 1943 and 1945; they examined 152 major allied air raids in Europe.
Sequences of radio pulses over a range of shortwave frequencies sent from 100 to 300 km above the surface of the planet reveal the height and concentration of electrons in the ionized part of the Earth's upper atmosphere.
The region, called the ionosphere – which includes the thermosphere and parts of the mesosphere and exosphere – is ionized by solar radiation. Highly variable, it can affect modern technologies such as radio communications, global positioning systems and radio telescopes.
According to the study, the electron concentration in the ionosphere has decreased considerably due to the shock waves caused by the bombs that explode near the surface of the Earth. The explosions have probably heated the upper atmosphere, improving the loss of ionization.
"It's amazing how ripples caused by man-made explosions can affect the limits of space," Scott said. "Each raid released the energy of at least 300 lightning strikes. The simple power involved allowed us to quantify the impact of events on the Earth's surface on the ionosphere. "
Air attacks on the railways, ports, cities and industrial districts in enemy territory occurred regularly during the Second World War.
"The crews involved in the raids reported that their planes had been damaged by the shockwaves of the bomb, although they were above the recommended height," said Patrick Major, professor and historian at the University of Reading.
People on the ground also remember being thrown into the air by pressure waves, and the windows and doors were torn off their hinges.
"The unprecedented power of these attacks has proven useful for scientists to assess the impact these events can have on hundreds of people. [miles] above the land, in addition to the devastation that they caused on the ground, "said Major.
To continue his research, the team is asking members of the public to contribute to the digitization of the first atmospheric data. They hope to better understand the impact of smaller bombardment raids and determine the minimum explosive energy required to trigger a detectable response in the ionosphere.
The Earth is not the only cosmic body to have an ionosphere – it turns out that our Moon has one too. NASA, meanwhile, has launched a giant balloon into the stratosphere to observe rare polar mesospheric clouds. Learn more about the atmosphere of the Earth here.
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