Long-Term Observations of Schumann Resonances at Portishead (UK)

Constructive interference of lightning-generated signals in the extremely low frequency (ELF) below 100 Hz is the source of a global electromagnetic phenomenon in the Earth’s atmosphere known as Schumann Resonances (SR). SR are excited at frequencies of 7.8, 14, 20, 26, … Hz, and their diurnal and seasonal intensity variations are largely dependent on changes in the location and magnitude of the major lightning centres in Southeast Asia, Africa, and South America. In the last five decades, extensive research has focused on reconstructing the spatial and temporal evolution in global lighting activity using SR measurements, and more recently on analysing the links to climate change, transient luminous events (TLE), and biological systems. In this study, a quasi-electrostatic antenna, primarily designed as a thunderstorm warning system, is for the first time applied to measure background variability in the SR band at an urban site in Southwest England. Data collected continuously from June 2015 for a 5-year period are suitably filtered and analysed showing that SR is the dominant contribution to the fair-weather displacement current measured by the sensor in the band 10–45 Hz. Diurnal and seasonal signal amplitude variations have been found to be consistent with previous studies and show the African-European lightning centre to prevail due to the shorter source-observer distance. Also, it is shown that long-term global changes in the ocean and land temperature, and the subsequent effect on the major lightning hotspots, may be responsible for the inter-annual variability of SR intensity, indicating that the largest increase occurred during the 2015–2016 super El-Niño episode.

FDTD analysis of ELF radio wave propagation in the spherical Earth-ionosphere waveguide and its validation based on analytical solutions

The FDTD model of electromagnetic wave propagation in the Earth-ionosphere cavity was developed under assumption of axisymmetric system, solving the reduced Maxwell’s equations in a 2D spherical coordinate system. The model was validated on different conductivity profiles for the electric and magnetic field components for various locations on Earth along the meridian. The characteristic electric and magnetic altitudes, the phase velocity and attenuation rate were calculated. We compared the results of numerical and analytical calculations and found good agreement between them. The undertaken FDTD modeling enables us to analyze the Schumann resonances and the propagation of individual lightning discharges occurring at various distances from the receiver. The developed model is particularly useful when analyzing ELF measurements.

Global Study of Human Heart Rhythm Synchronization with the Earth’s Time Varying Magnetic Field

Changes in geomagnetic conditions have been shown to affect the rhythms produced by the brain and heart and that human autonomic nervous system activity reflected in heart rate variability (HRV) over longer time periods can synchronize to changes in the amplitude of resonant frequencies produced by geomagnetic field-line and Schumann resonances. During a 15-day period, 104 participants located in California, Lithuania, Saudi Arabia, New Zealand, and England underwent continuous ambulatory HRV monitoring. The local time varying magnetic field (LMF) intensity was obtained using a time synchronized and calibrated network of magnetometers located at five monitoring sites in the same geographical locations as the participant groups. This paper focuses on the results of an experiment conducted within the larger study where all of the participants simultaneously did a heart-focused meditation called a Heart Lock-In (HLI) for a 15-min period. The participant’s level of HRV coherence and HRV synchronization to each other before, during and after the HLI and the synchronization between participants’ HRV and local time varying magnetic field power during each 24-h period were computed for each participant and group with near-optimal chaotic attractor embedding techniques. In analysis of the participants HRV coherence before, during and after the HLI, most of the groups showed significantly increased coherence during the HLI period. The pairwise heart rhythm synchronization between participants’ in each group was assessed by determining the Euclidean distance of the optimal time lag vectors of each participant to all other participants in their group. The group member’s heart rhythms were significantly more synchronized with each other during the HLI period in all the groups. The participants’ daily LMF-HRV-synchronization was calculated for each day over an 11-day period, which provided a 5-day period before, the day of and 5-days after the HLI day. The only day where all the groups HRV was positively correlated with the LMF was on the day of the HLI and the synchronization between the HRV and LMF for all the groups was significantly higher than most of the other days.

Locating Schumann Resonant Frequencies on a Single Particle Radiation Patterns Using Golden Ratio Spiral and Octave Relationship of Schumann Points.

<p>Although lightning discharge is not the only source or only physical phenomenon that affects the Schumann resonances, they have the highest contribution to the Schumann resonances oscillating between the ground the ionosphere. Schumann resonances are predicted through several different numerical models such as the transmission-line matrix model or partially uniform knee model. This contribution reports a different prediction method for Schumann resonances derived from the first principle of fundamental physics combining both particle radiation patterns and the mathematical concept of the Golden ratio. This prediction allows the physical understanding of where Schumann resonances originate from radiation emitted by a particle that involves many frequencies that are not related to Schumann resonances. In addition, this method allows predicting the wave propagation direction of each frequency value in the Schumann frequency spectrum. Particles accelerated by lightning leader tip electric fields are capable of contributing most of the Schumann resonances. The radiation pattern of a single particle consists of many frequencies. There are only specific ones within this pattern that contribute to the Schumann radiation. The vast majority of Schumann resonances distribute quite nicely obeying the Golden ratio interval. This property, used in conjunction with the full single-particle radiation patterns, also revealed that high-frequency forward-backward peaking radiation patterns, as well as low-frequency radiation patterns, can contribute to Schumann resonances. This method allows to locate them on the full radiation pattern. A theoretical analysis using the Golden ratio spiral, predict that there are more Schumann resonances in the high-frequency forward-backward peaking radiation pattern of a relativistic particle than low-frequency dipole radiation pattern. Extending the idea to an octave that identifies the identical sounding notes with different frequencies in standing waves. By knowing the value of the initial Schumann resonant frequency, this method allows us to predict the magnitude of other Schumann resonances on the radiation pattern of a single accelerated charged particle conveniently. In addition, it also allows us to find and match Schumann resonances that are on the same radiation lobe, which is named electromagnetic Schumann octaves. Furthermore, it is important to find Schumann octaves as they propagate in the same direction and have a higher likelihood of wave interference.</p>

Detection of charged organic grains at the surface of Titan with the EFIELD/DraGMet sensor on board Dragonfly

<p>Titan, the largest moon of Saturn, is the place in the Solar System showing the most Earth-like landscapes. Titan’s dense atmosphere and cold temperatures enable a complex methane hydrological cycle that have shaped the surface, very similarly to the water cycle on Earth. Titan has another peculiar feature: a wealth of organic grains is created by photochemistry in its atmosphere and progressively deposited at its surface. Such atmospheric production of organics likely occurred on Earth before the apparition of life; that is the reason why a better understanding of the formation processes, chemical composition and physical properties of these grains is of great interest.</p><p>The Dragonfly mission has recently been selected by NASA to explore Titan’s surface with a rotorcraft circa 2035 (Lorenz et al., 2018). Dragonfly will explore a region of organic sand dunes with monthly flights of a few kilometres each aiming to an impact crater named Selk. In addition to chemical analyses, Dragonfly is equipped with several sensors intended to characterize its environment. Among them, as part of the Dragonfly Geophysical and Meteorological (DraGMet) package, the EFIELD instrument will record the AC electric field at low frequencies (~5-100 Hz).</p><p>EFIELD consists in two spherical electrodes accommodated at different locations on the rotorcraft. The main scientific objective of EFIELD is to measure Schumann Resonances on Titan. Such resonances may have been detected by the Huygens probe in 2005 (unless it was an artefact of probe motion; Lorenz and Le Gall, 2020) and would be an indication of the existence of an underground global salty ocean (Beghin et al., 2012). Another scientific objective of EFIELD is the detection and characterization of charged grains. This work is dedicated to this secondary objective.</p><p>The exploration area of Dragonfly is covered by sand grains, most likely organic in nature, maybe mixed with ice. Surface winds can sometimes put them in saltation or suspension. In the process, these organic grains are likely to get charged by friction (triboelectric effect; Méndez-Harper et al., 2017), and would then induce a perturbation on the electric field detectable by the EFIELD antennas. To estimate the significance of this perturbation and test the possibility to measure it, we have built a numerical model that simulates the trajectory of charged particles in the probe environment, subjected to turbulent wind flows, gravity and electrostatic forces. First results show that charged particles will induce a strong measurable signal on the EFIELD spectra. We are thus currently investigating how these spectra can be used to derive information on the grains (number, charge, size or density). On Titan, EFIELD will work in synergy with wind sensors and a microscopic imager that will observe grains deposited at the surface.</p><p>The next steps in our simulations will be to account for the perturbations induced by the nearby body of Dragonfly. In parallel, we are building a prototype antenna to test it and check the ability of our model to reproduce its measurements in the laboratory and in the frame of field campaigns.</p>