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An explanation of the strongest natural radio waves on Earth

edit£ºphyqianyg  date£º2017-03-09 10:40:27   Visits :164

    On Earth, the strongest radio waves of natural origin are related to lightning. They consist of two separated pulses and were discovered more than two decades ago by a satellite in space. It is commonly believed that they are produced from an in-cloud lightning. The 1st pulse is along a direct lightning-to-satellite path and the 2nd one is an echo by reflection from the ground. However, this reflection hypothesis cannot explain completely uncorrelated inner structures of the two pulses. Recently, Prof. Hui-Chun Wu at the Institute for Fusion Theory and Simulation (IFTS) and Department of Physics proposes [1] a new explanation of these radio signals. A cloud-to-ground lightning propagates downward in a stepped process, and each lightning step emits energetic electrons. The electrons from the last two steps can strike the ground and produce two radio pulses skyward. The pulse interval is consistent with the time between the lightning steps. Two independent electron sources account for the uncorrelated radio pulses. The model also successfully explains many other properties: intensity, polarization, coherence and bimodal feature.
    Additionally, the work supplies a strong physical support to the recent microwave theory of ball lightning [2] by Prof. Hui-Chun Wu. He assumes that an intense electron beam appears from a lightning tip.This electron beam strikes the ground and excites ultra-intense microwave radiation. The microwave in air plasmas further naturally evolves into a spherical plasma bubble, which stably traps the radiation. This new theory can explain most of the features of ball lightning, and it has gained strong interests in the community. A popular scientific article on this topic is available on Nautilus [3].
[1] H.-C. Wu, Origin of trans-ionospheric pulse pairs, Geophys. Res. Lett. (2017).
[2] H.-C. Wu, Relativistic-microwave theory of ball lightning, Sci. Rep. 6, 28263 (2016).