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  1. Abstract

    Optical observations of transient luminous events and remote-sensing of the lower ionosphere with low-frequency radio waves have demonstrated that thunderstorms and lightning can have substantial impacts in the nighttime ionospheric D region. However, it remains a challenge to quantify such effects in the daytime lower ionosphere. The wealth of electron density data acquired over the years by the Arecibo Observatory incoherent scatter radar (ISR) with high vertical spatial resolution (300-m in the present study), combined with its tropical location in a region of high lightning activity, indicate a potentially transformative pathway to address this issue. Through a systematic survey, we show that daytime sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). These changes typically correspond to electron density depletions in the D and E region. The survey also shows that these disturbances are different than the ones associated with solar flares, which tend to have longer duration and most often correspond to an increase in the local electron density content.

  2. Free, publicly-accessible full text available July 26, 2023
  3. Runaway electron acceleration is the keystone process responsible for the production of energetic radiation by lightning and thunderstorms. In the laboratory, it remains undetermined if runaway electrons are merely a consequence of high electric fields produced at the ionization fronts of electrical discharges, or if they impact the discharge formation and propagation. In this work, we simulate photon pileup in a detector next to a spark gap. We compare laboratory measurements to ensembles of monoenergetic electron beam simulations performed with Geant4 (using the Monte Carlo method). First, we describe the x-ray emission properties of monoenergetic beams with initial energies in the 20 to 75 keV range. Second, we introduce a series of techniques to combine monoenergetic beams to produce general-shape electron energy spectra. Third, we proceed to attempt to fit the experimental data collected in the laboratory, and to discuss the ambiguities created by photon pileup and how it constrains the amount of information that can be inferred from the measurements. We show that pileup ambiguities arise from the fact that every single monoenergetic electron beam produces photon deposited energy spectra of similar qualitative shape and that increasing the electron count in any beam has the same qualitative effect of shiftingmore »the peak of the deposited energy spectrum toward higher energies. The best agreement between simulations and measurements yields a mean average error of 8.6% and a R-squared value of 0.74.« less
    Free, publicly-accessible full text available May 1, 2023
  4. In the last couple of decades, substantial research has been dedicated to understanding the coupling between atmospheric regions. Research on transient luminous events (TLEs) appeared and quickly intensified with the promise of TLEs serving as an optical remote sensing tool of the mesosphere and lower ionosphere. However, to date it remains challenging to obtain quantitative estimates of electron density changes in the ionospheric D region due to underlying lightning and thunderstorms. Arecibo’s incoherent scatter radar (ISR) capabilities for measuring ionospheric electron density with high resolution (300-m spatial resolution in the present study), combined with its tropical location in a region of high lightning incidence rates, indicate a potentially transformative pathway to address this problem. Through a systematic survey, we show that sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). Electron density changes happening coincidentally with lightning activity have typical amplitudes of 10–90% between 80–90 km altitude, and in a selected number of cases can be reasonably correlated to underlying lightning activity.