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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 5 | Copyright
Ann. Geophys., 36, 1243-1254, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 26 Sep 2018

Regular paper | 26 Sep 2018

The ionospheric response over the UK to major bombing raids during World War II

Christopher J. Scott1 and Patrick Major2 Christopher J. Scott and Patrick Major
  • 1Department of Meteorology, University of Reading, Berkshire, UK
  • 2Department of History, University of Reading, Berkshire, UK

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.

Publications Copernicus
Short summary
The variability of the Earth's ionosphere (the electrified region of the Earth's upper atmosphere) results from external forcing from above (through solar activity and space weather effects) and from below (via natural sources such as lightning storms and tectonics). Bombing raids over Europe during World War II were used to determine the quantitative impact of explosions on the ionosphere. It was found that raids using more than 300 tonnes of explosives weakened the ionosphere for up to 5 h.
The variability of the Earth's ionosphere (the electrified region of the Earth's upper...