https://www.bbc.com/news/science-environment-45655149World War II bombs 'felt in space'
By Laura Foster BBC Science News
26 September 2018
The bombs used by Allied forces during World War II were so large, they weakened the Earth's upper atmosphere.
The air raids turned towns to rubble and ash, but now new research shows shockwaves could be felt up to 1,000 km above the UK.
Chris Scott, from the University of Reading said: "I was absolutely astonished [when I found out].
"Each raid released the energy of at least 300 lightning strikes."
It's now hoped the research will give us a better understanding of how natural forces such as lightning, volcanic eruptions and earthquakes can affect Earth's upper atmosphere.
How do we know this happened?
Researchers studied daily records kept at the Radio Research Centre in Slough, UK.
They looked at how the concentration of electrons changed in the upper atmosphere around the time of 152 Allied air raids in Europe - including raids on Berlin and those in support of the Normandy landings.
The data showed the concentration of electrons fell significantly when a bomb was detonated, which in turn heated the upper atmosphere.
This caused a small but significant depletion in the ionosphere above Slough, even though the bombs were deployed hundreds of miles away.
But Chris Scott admits "these were very temporary effects which heated the atmosphere very slightly."
"The effects on the ionosphere would only have lasted until the heat dissipated."
Why do we need to know about the ionosphere?
It is a layer of the Earth's atmosphere which can affect radio communications, GPS systems, radio telescopes and even some understanding of weather systems.
Chris Scott said: "This [research] is really important if we're going to understand the ionosphere as a whole.
"We know the ionosphere is controlled by solar activity but it varies much more than can currently be explained."
The results are published in the European Geosciences Union journal, Annales Geophysicae.
Pretty impressive, even if the difference was slight, considering the lowest parts of the ionosphere start at 80km high, and the top is around 1000km above us, which is well above the orbit of the space station. Another example of how sensitive the air above us really is, how little mass really exists between the surface and open space. While some WW2 bombs were pretty big the vast majority were well under 2,000lb weight, but the collective heat release of these attacks does add up. Something like 1 megaton of high explosives was used in WW2.
Since the article is a bit thin, I'm also including the abstract of the actual research paper, based on radio study records from the war.
Abstract. The Earth's ionosphere is subject to disturbance from above (via solar variability and space-weather effects) and from below (such as tectonic activity, thunderstorms and sudden stratospheric warmings). Identifying the relative contribution of these effects remains challenging, despite recent advances in spacecraft monitoring near-Earth space. Man-made explosions provide a quantifiable proxy for natural terrestrial sources, enabling their impact on ionospheric variability to be studied. In this paper, the contribution of ground-based disturbances to ionospheric variability is investigated by considering the response of the ionospheric F2 layer over Slough, UK, to 152 major bombing raids over Europe during World War II, using a superposed epoch analysis. The median response of the F2 layer is a significant decrease in peak electron concentration ( ∼ 0.3MHz decrease in foF2). This response is consistent with wave energy heating the thermosphere, enhancing the (temperature-dependent) loss rate of O+ ions. The analysis was repeated for a range of thresholds in both time of bombing before the (noon) ionospheric measurement and tonnage of bombs dropped per raid. It was found that significant ( ∼ 2–3σ) deviations from the mean occurred for events occurring between approximately 3 and 7h ahead of the noon ionospheric measurements and for raids using a minimum of between 100 and 800t of high explosives. The most significant ionospheric response (2.99σ) occurred for 20 raids up to 5h before the ionospheric measurement, each with a minimum of 300t of explosives. To ensure that the observed ionospheric response cannot be attributable to space-weather sources, the analysis was restricted to those events for which the geomagnetic Ap index was less than 48 (Kp < 5). Digitisation of the early ionospheric data would enable the investigation into the response of additional ionospheric parameters (sporadic E, E and F1 layer heights and peak concentrations). One metric ton of TNT has an explosive energy of 4.184×109J, which is of the same order of energy as a cloud to ground lightning stroke. Since the occurrence of lightning has distinctive diurnal and seasonal cycles, it is feasible that a similar mechanism could contribute to the observed seasonal anomaly in ionospheric F-region electron concentrations. Further investigation, using less extreme examples, is required to determine the minimum explosive energy required to generate a detectable ionospheric response.
So you basically you only need to drop a minimal of 100 tons of bombs, which would equal to 25-100 typical WW2 bombing planes, to start to affect the ionosphere.