Lightning Excitation of the Ionospheric Alfvén Resonator

  • Author / Creator
    Nokes, Charles D. A.
  • The ionospheric Alfvén resonator (IAR) is an area of space that, due to sharp Alfvén speed gradients, has the ability to trap electromagnetic plasma wave energy, where it bounces in the Alfvén mode between near-Earth space and the lower ionosphere. Here we present research that, by comparing induction coil magnetometer data from the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) with world lightning occurrence data from the World Wide Lightning Location Network (WWLLN), has revealed strong evidence that energy released in terrestrial lightning storms can enter this resonator. Energy from lightning strikes is ducted through the Earth-Ionosphere cavity, generating the well-defined Schumann resonances (SR) with a fundamental frequency of ~7.8 Hz. Our results show that in addition to the Schumann resonances, the lightning energy perturbs magnetic field lines as it propagates, generating Alfvén waves that travel up the magnetic field lines towards near-Earth space, and in regions where the ionospheric Alfvén resonator is active, these Alfvén waves are reflected back down from the peak in the Alfvén speed, resulting in one or more echo pulses in the time series magnetometer data. Using the superposed epoch analysis technique reveals two critical characteristics of this paradigm: 1) the pulse-echo(s) signal in the time series, which occur on the scale of 1-2 seconds, is defined by the characteristics of the local resonator, and this is most clearly shown by the spectra of the time series signal; and 2) this pulse-echo signal in the time series has been measured for lightning occurring at large distances, beyond 8000 km from the magnetometer instrument, which contradicts earlier assumptions that the lightning pulse needed to be local (or less than 2000 km away) from the ionospheric Alfvén resonator active region of the ionosphere. Our results suggest the coupling between SR and IAR is a global phenomenon. Lightning might act as a continuous source for Alfvén wave energy input into the magnetosphere with potentially important but heretofore unknown consequences for magnetospheric physics. This provides an interface between space weather and the terrestrial global electric circuit. Future work should reveal more details about this previously unknown pathway for magnetosphere-ionosphere-atmosphere coupling.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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