The bombings of the Second World War weakened the upper atmosphere at the edge of space

The electrified upper atmosphere of the Earth (the ionosphere) undergoes many natural variations, changing with the days and seasons. The ionosphere can also be affected by some major events, including solar flares, volcanic eruptions, lightning – and massive bombs dropped on Germany during World War II. These bombardments produced shock waves strong enough to weaken the ionosphere close to space.

This is the conclusion of a new study by researchers from the University of Reading, published in the journal Annals Geophysicae. More than a historical curiosity, the results are important because ionospheric disturbances can disrupt key communication technologies, including GPS systems, radio telescopes and radio communications.

The air raids carried out by German and Allied forces in the 1940s were aimed at removing critical industrial and political infrastructures, and if civilians were in the line of fire, so be it. (The Allied bombing of Hamburg in 1943 would have caused the death of 45,000 people.) The intensification of the fear of dying among the locals has been key to the strategy as the physical destruction caused by the massive bombs has dropped . The largest bombs, weighing up to 10 tons, were powerful enough to blow up the roofs of buildings, sending intense shock waves, not only through the streets, but also into the heavens.

"The locals would regularly remember to have been thrown into the air by the surging air pressure waves."

"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," says Patrick Major, co-author and historian. explosive air mines, and windows and doors fly off their hinges. There were even rumors that wrapping wet towels on the face could save people in shelters from collapsing lungs, leaving the victims intact.

The effects have also apparently spread in the atmosphere. The ionosphere is composed of three different ionized regions within the different atmospheric layers of the Earth (the upper mesosphere and the lower and upper thermosphere in particular). This means that they have a significantly higher density of electrically charged atoms and molecules than the surrounding regions. This occurs because the high-energy X-rays and ultraviolet rays of the Sun collide with atoms and molecules in the atmosphere with enough energy to remove the electrons, thus creating ions (atoms). and molecules with missing electrons) and free electrons.

In the absence of satellite technology, radio operators of the time often used the ionosphere to increase the range of their signals, some frequencies reflecting the electrically charged particles as a mirror. But the ionosphere is so variable that it was crucial to track its daily changes by sending radio pulse sequences at short wave frequencies into the sky and seeing how they were damped. or redirected.

The Slough Radio Research Center retains detailed information on all of this data, which has been beneficial to the reading team. Major and his co-authors studied ionospheric response surveys between 1943 and 1945, looking for changes in height and electron concentration of ionization in the upper atmosphere above the ionospheric response. England in response to the bombings.

They compared these data with historical records of the approximately 152 Allied raids in Europe during this period. London is closer to Slough, but according to Major, the German bombing of the famous London "Blitz" was so frequent that it was almost continuous, making it difficult to distinguish between ionospheric effects due to bombing and those with seasonal variation. usual.

Major and his colleagues found a marked decrease in the concentration of electrons – a loss of ionization – in the ionosphere at the time of air raids, probably due to a heating effect of shock waves produced by bombing. This is a strong proof of principle for the technique in terms of assessing how the ionosphere changes in response to such events. "The unprecedented power of these attacks has proven useful in assessing the impact these events may have on hundreds of kilometers above the Earth, in addition to the devastation they have caused on the ground," Major explains.

Annals Geophysicae, 2018. DOI: 10.5194 / angeo-36-1243-2018, (About the DOIs).