Unusual radar echoes in the sky may finally have been explained
DOI: 10.1063/PT.5.029803
Science : For several decades, unusual radar signals have been spotted that appear at dawn at an altitude of 150 km, grow stronger as they descend to 20 km, and then rise back to 150 km before disappearing at sunset. Because the signals get weaker during solar eclipses and stronger during solar flares, the Sun may be the source of the effect. But what causes it has not been clear. Now Meers Oppenheim and Yakov Dimant of Boston University suggest that extremely high-energy solar UV radiation could be ionizing gas molecules in a thin band of the upper atmosphere at an altitude of 150 km. Earth’s magnetic field would then cause the freed electrons and the ionized molecules to rearrange themselves into areas of varying density, which can be detected by radar.
