A B-17 bombing Marienberg, Germany, in October 1943.
A B-17 bombing Marienberg, Germany, in October 1943. U.S. Office for Emergency Management/Public Domain

Of course, the bombs dropped from planes during World War II wreaked havoc on the ground, claiming lives and reducing buildings to rubble. But according to new research in the European Geosciences Union journal Annales Geophysicae, the bombs’ effects also stretched high into the sky—all the way to the ionosphere, the portion of the upper atmosphere that reaches as much as 620 miles above the wreckage.

For this study, researchers at the University of Reading analyzed records from the Radio Research Centre in the English city of Slough. For years, the Centre collected daily data about shortwave radio pulses. By analyzing a trove of these spanning 1943 through 1945, and comparing fluctuations against time-stamped air-raid warnings and eye-witness accounts, the researchers were able to piece together a picture of how bombs briefly changed the sky—even when they detonated pretty far away.

Instead of measuring the sky-high impact of Nazi attacks, the researchers trained their focus on Allied campaigns across Europe. Allies’ four-engine planes could haul larger numbers of bombs packed with huge amounts of TNT, the authors write; also, it was easier to isolate data for their bombing sprees, whereas Nazi air raids were sometimes more or less continuous.

B-24 planes dropping bombs over occupied Europe in 1943.
B-24 planes dropping bombs over occupied Europe in 1943. U.S. Army Air Forces/Public Domain

Looking at records corresponding to 152 air raids, the authors concluded that the bombs temporarily weakened the ionosphere by decreasing the concentration of charged electrons. (The effects appeared to dissipate after a day or so.) A single metric ton of TNT delivers as much explosive energy as a cloud-to-ground lighting stroke, the authors write; a typical air raid rained down the equivalent of roughly 300 bolts of lightning. “Aircrew involved in the raids reported having their aircraft damaged by the bomb shockwaves, despite being above the recommended height,” said co-author Patrick Major, a historian at the University of Reading, in a statement.

The researchers didn’t investigate the extent to which smaller explosions might still register up there, near the fringe of space. This region is a bit of a marginal zone, and it behooves us to learn about it—fluctuations there, in the turf of radio waves and satellites that beam GPS data, affect us here on Earth. More research could help researchers gauge how other terrestrial events, such as earthquakes or eruptions, shape the sky high above us, and our lives down below.