ULF electromagnetic noise due to random variations of background atmospheric current and conductivity

Abstract

[1] A mechanism of ULF electromagnetic noise generation due to random fluctuations of the atmospheric conductivity and background currents was examined. Current fluctuations similar to 1/f noise, or flicker noise, are assumed to develop inside large-scale atmospheric inhomogeneities such as thunderstorms, hurricanes, mesoscale convective systems, etc. The random current fields are assumed to be steady, uniform, and isotropic inside the inhomogeneity, which, in turn, implies that the spectral density of the process is delta correlated. A correlation radius of the random process is supposed to be dependent on gas transfer and on the acoustic wave propagation due to pressure and temperature gradients in the atmosphere. To relate the electromagnetic spectra with current fields, a transfer matrix was found, and then the correlation matrix and power spectra of the random electromagnetic field were calculated. It was shown that the large-scale random fluctuations of the atmospheric background current are capable of sustaining generation of the ULF magnetic noise that can be detected on the ground. The spectral index of magnetic noise was found to be 1.5, which is consistent with observation in the 10 À2 to 10 À4 Hz frequency range.Citation: Surkov, V. V., and M. Hayakawa (2007), ULF electromagnetic noise due to random variations of background atmospheric current and conductivity,

Natural electromagnetic ULF noise due to fluctuations of ionospheric currents

“…The lines 3 and 3′, which correspond to the nighttime parameters of the ionosphere, lies below the experimental data. Notice that the same tendency appears as the atmospheric current fluctuations is considered as a possible mechanism for the ULF electromagnetic noise [ Surkov and Hayakawa , 2007]. To explain this discrepancy with observations, one may assume the presence of supplementary sources, which contribute to the ULF noise at nighttime.…”

“…Such fluctuations may propagate with the velocities of acoustic and atmospheric gravity waves, which frequently occur at the altitudes of the E ‐layer. In this picture the correlation radius of the random fields can be roughly estimated as [ Surkov and Hayakawa , 2007], Here V a ( ω ) denotes the acoustic wave velocity or the mass velocity of the neutrals and T stands for a typical period of ionospheric parameter variations.…”

“…Such fluctuations may propagate with the velocities of acoustic and atmospheric gravity waves, which frequently occur at the altitudes of the E-layer. In this picture the correlation radius of the random fields can be roughly estimated as [Surkov and Hayakawa, 2007],…”

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1] An origin of natural electromagnetic noise observed on the ground surface in the frequency range 10 À4 -10 À2 Hz was examined. Following a recent paper by Surkov and Hayakawa (2007), a flicker noise or 1/f noise, provided by random currents, is treated as a possible source of the ULF electromagnetic noise. In contrast to the cited paper, MHD wave incident on the ionosphere and neutral gas flow in the altitude range of conducting E layer of the ionosphere are considered to be a candidate mechanism for random current fluctuations, which in turn produce random electromagnetic fluctuations in the atmosphere.

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A remote-control datalogger for large-scale resistivity surveys and robust processing of its signals using a software lock-in approach

“…To calculate the broadband noise level we cut out all harmonics of the ERT signal and consider only the frequency range from DC to the 15th harmonics. Unlike Günther et al (2011) or Agricola et al (2017) we do not assume a constant noise floor over the frequency axis but assume a 1/f decrease that is often observed (Surkov and Hayakawa, 2007). Therefore we carry out a non-linear fit with a noise model consisting of a noise floor and an inverse f contribution:…”