Andrzej Kulak

ELF Propagation Parameters for the Ground-Ionosphere Waveguide With Finite Ground Conductivity

In the extremely low frequency (ELF) range, the space between the ground and ionosphere forms a spherical waveguide. When studying the ELF radio-wave propagation on Earth using analytical models, it is commonly assumed that the ground has perfect conductivity. In some planetary applications, the ground conductivity is so low that it has a significant influence on the radio-wave propagation in the ELF range and it has to be included in the model. This issue has not been resolved in a satisfactory way yet. In this paper, we analyze the penetration of the ground by an electromagnetic wave traveling along the surface and we propose a solution that allows including ground parameters in the frequently used 2-D analytical model of the ground-ionosphere waveguide. The presented calculations show that in most cases on Earth, the differences with such a model are small, up to a few percent for phase velocity.

An unusual sequence of sprites followed by a secondary TLE: An analysis of ELF radio measurements and optical observations

We present an extraordinary case of sprites in rapid succession—four sprite clusters in only 400 ms—followed by a secondary jet. Simultaneous ELF and optical observations, as well as lightning data, enabled us to thoroughly document this unique event. Locations of the transient luminous events (TLEs) were triangulated using video recordings from Nydek (Czech Republic) and Sopron (Hungary). We found that sprites were displaced up to 70 km from their parent lightning. The current moment waveform and charge moment changes associated with the event were reconstructed from the ELF electromagnetic signature recorded at the Hylaty station (Poland) by a new method. The results suggest that both a short-delayed and a long-delayed sprite were generated by a single positive cloud-to-ground discharge that had an intense continuing current. It had an unusual progression and lasted 200 ms. A large increase in the current moment during the development of a massive carrot sprite provides evidence in favor of sprite current. Our results also support the formation of an electric environment hypothesized to be necessary for the generation of the secondary TLEs.

An Analytical Model of ELF Radiowave Propagation in Ground-Ionosphere Waveguides With a Multilayered Ground

A planetary crust with a low electric conductivity has a strong influence on extremely low frequency (ELF) radiowave propagation in the ground-ionosphere waveguide due to the penetration of the ground by the waves electromagnetic field. The amount of influence it has depends on the actual structure of the ground. Accurate models of radiowave propagation in the ELF range are essential in the study of atmospheric discharges and remote sensing applications. Analytical models are still of primary interest when trying to find inverse solutions and when dealing with large objects such as spherical waveguides that consists of a planetary ground and ionosphere. In this paper, we analyze the influence of a multilayered finite conductivity ground on the propagation of ELF electromagnetic waves in the ground-ionosphere waveguide. We have developed equations that enable us to include different ground models in propagation equations using the concept of complex altitudes, and applied them to the study of ELF electromagnetic field pulses on Mars. This study shows that the structure of the ground and its electrical conductivity has a strong influence on the observed waveforms. Therefore, ELF pulses can serve as a tool for probing planetary grounds. The presented model can also be used to study Schumann resonances.

Study of the Periodicities of Lightning Activity in Three Main Thunderstorm Centers Based on Schumann Resonance Measurements

Abstract Time variations of lightning activity in the three main tropical thunderstorm centers located in the Maritime Continent (Pakistan, India, Southeast Asia, Indonesia, and Australia), Africa, and the Americas are analyzed using a lightning activity index IRS, which is calculated from the resonances of magnetic field in the extremely low frequency range—the Schumann resonances—which were observed at Hylaty station (Poland) in the time interval July 2005–May 2006. Power spectrum analysis of the IRS series is carried out for this time interval. The annual and semiannual variations are shown in all of the series together with the following characteristic periodicities: 45 (Madden–Julian oscillation), 17.6, 13.5, and 4.8 days, seen mainly in the series describing the lightning activity of the Maritime Continent. In addition, maps of the dynamical power spectrum are constructed. They present variability both in the values of characteristic periods 26–30, 17–22, 12–14, 9–10, and 5–7 days and in their durat...

Novel analysis of a sudden ionospheric disturbance using Schumann resonance measurements

A spherical cavity between Earth and the lower ionosphere forms a global resonator for Extremely Low Frequency electromagnetic waves. Constant thunderstorm activity leads to the formation of a resonance field in the cavity, known as the Schumann resonance. Solar flare generated Sudden Ionospheric Disturbances (SID) modify the ionosphere affecting the ground-based radio communication systems. They are also expected to modify radiowave propagation in the cavity. In this paper, the Schumann Resonance spectral decomposition method is used for the first time to study the cavity resonance frequencies during the SID accompanying a strong X2.1 solar flare. We analyzed rapid changes in the frequencies and Q factors of the first five resonance modes using a 5 min timescale. The observed frequency shifts were compared to the ionizing solar flare fluxes in the UV, X-ray, and high-energy γ rays.

Harmonic Analysis of Time Variations Observed in the Solar Radio Flux Measured at 810 MHz from 1957 to 2004

In recent years evidence has accumulated that nearby spiral galaxies are surrounded by massive haloes of neutral and ionised gas. These gaseous haloes rotate more slowly than the disks and show inflow motions. They are clearly analogous to the High Velocity Clouds of the Milky Way. We show that these haloes cannot be produced by a galactic fountain process (supernova outflows from the disk) where the fountain gas conserves its angular momentum. Making this gas interact with a pre-existing hot corona does not solve the problem. These results point at the need for a substantial accretion of low angular momentum material from the IGM.

Globally coherent short duration magnetic field transients and their effect on ground based gravitational-wave detectors

It has been recognized that the magnetic fields from the Schumann resonances could affect the search for a stochastic gravitational-wave background by LIGO and Virgo. Presented here are the observations of short duration magnetic field transients that are coincident in the magnetometers at the LIGO and Virgo sites. Data from low-noise magnetometers in Poland and Colorado, USA, are also used and show short duration magnetic transients of global extent. We measure at least 2.3 coincident (between Poland and Colorado) magnetic transient events per day where one of the pulses exceeds 200 pT. Given the recently measured values of the magnetic coupling to differential arm motion for Advanced LIGO, there would be a few events per day that would appear simultaneously at the gravitational-wave detector sites and could move the test masses of order

Subtraction of correlated noise in global networks of gravitational-wave interferometers

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Application of the Schumann resonance spectral decomposition in characterizing the main African thunderstorm center

m. We confirm that in the advanced detector era short duration transient gravitational-wave searches must account for correlated magnetic field noise in the global detector network.

Comparison of the charge moment change calculated from electrostatic analysis and from ELF radio observations

The recent discovery of merging black holes suggests that a stochastic gravitational-wave background is within reach of the advanced detector network operating at design sensitivity. However, correlated magnetic noise from Schumann resonances threatens to contaminate observation of a stochastic background. In this paper, we report on the first effort to eliminate intercontinental correlated noise from Schumann resonances using Wiener filtering. Using magnetometers as proxies for gravitational-wave detectors, we demonstrate as much as a factor of two reduction in the coherence between magnetometers on different continents. While much work remains to be done, our results constitute a proof-of-principle and motivate follow-up studies with a dedicated array of magnetometers.