Impact of WWII bombing raids felt at edge of space: Study

Bombing raids by Allied forces during the Second World War not only caused devastation on the ground but also sent shockwaves through the Earth's atmosphere which were detected at the edge of space, according to a study.

Researchers at the University of Reading in the UK have revealed the shockwaves produced by huge bombs dropped by Allied planes on European cities were big enough to weaken the electrified upper atmosphere -- the ionosphere -- above the UK, 1,000 kilometres (km) away.

Scientists are using the findings, published in the journal Annales Geophysicae, to understand how natural forces from below, like lightning, volcanic eruptions and earthquakes, affect Earth's upper atmosphere.

"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," said Chris Scott, a professor at the University of Reading.

"But the impact of these bombs way up in the Earth's atmosphere has never been realised until now," Scott said.

"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," he said.

Researchers looked at daily records at the Radio Research Centre in Slough, UK, collected between 1943-45.

Sequences of radio pulses over a range of shortwave frequencies were sent 100-300km above the Earth's surface to reveal the height and electron concentration of ionisation within the upper atmosphere, they said.

The strength of the ionosphere is known to be strongly influenced by solar activity, but the ionosphere is far more variable than can be explained by current modelling.

The ionosphere affects modern technologies such as radio communications, the Global Positioning System (GPS), radio telescopes and some early warning radar, however the extent of the impact on radio communications during the Second World War is unclear.

Researchers studied the ionosphere response records around the time of 152 large Allied air raids in Europe and found the electron concentration significantly decreased due to the shockwaves caused by the bombs detonating near the Earth's surface.

This is thought to have heated the upper atmosphere, enhancing the loss of ionisation.

Although the London 'Blitz' bombing was much closer to Slough, the continuous nature of these attacks and the fact there is far less surviving information about them made it more challenging to separate the impact of these explosions from natural seasonal variation, researchers said.

Detailed records of the Allied raids reveal their four-engine planes routinely carried much larger bombs than the German Luftwaffe's two-engine planes could. These included the 'Grand Slam', which weighed up to 10 tonnes, they said.