A Novel Population of Slow Magnetosonic Waves and a Method for the Observation of the Roots of Plasma Bubbles in the Lower Ionosphere

Abstract

The mean global rate of lightning is 60 flashes/s (Burgesser, 2017) and is concentrated most strongly in the mid-latitude continental regions. The high global rate of lightning strokes, together with the low attenuation at low frequencies leads to the establishment of standing wave resonances within the Earth Ionospheric Waveguide (EIWG). Within the EIWG, the wave attenuation in the frequency range below 100 Hz is roughly 0.5 dB/Mm according to (Chapman et al., 1966), so that such low frequency waves may travel several times around the globe before losing most of their energy. The propagation of electromagnetic waves in the EIWG is discussed most extensively by Nickolaenko and Hayakawa (2002), see also (Budden, 1957;Jackson, 1975;Schumann, 1952). The resonances of the EIWG are known as the Schumann resonances (SRs). The transient vertical electric and horizontal magnetic fields at great distances from an individual strong lightning stroke, designated Q-bursts by Ogawa et al. (1967), appear as bipolar pulses in the time domain according to Nickolaenko et al. (2004), comprising a series of diminishing intensity delayed pulses corresponding to multiple Earth circuits.If the EIWG was a lossless, perfectly spherical cavity, the SR eigenfrequencies would bewhere R e is the Earth's radius, c is the speed of light, and n is the number of the eigenmode. In the actual EIWG, the frequencies of the lowest eigenmodes are only slightly lower than the values given by Equation 1, with observed values for the five lowest eigenmodes of 7.8, 14.1, 20.3, 26.3, and 32.5 Hz as listed in table 1 of Chapman et al. (1966). The corresponding quality factor Q values are 4, 4.5, 5, 5.5, and 6 for these resonances. Q values for a resonance at a given frequency are commonly defined as the ratio of the resonance frequency to

Observations of the Roots of Plasma Bubbles: Are They Sometimes Foamy?

“…Section 5 presents a physical model for “foamy” plasma. The various observations in Bennett (2023) and the new observations in the present paper are interpreted in terms of this model. Section 6 provides further discussion and conclusions.…”

“…Examination of the numerous examples shown in Figures 1 and 2 and the figures in Supporting Information S1 further reveals that the unusual, nearly dispersionless spikes in the scalograms do not usually extend much above a few kHz. From the dispersion relations for fast magnetosonic waves traveling in a primarily O + plasma, as shown in Figure 1d of Bennett (2023), this frequency corresponds to wavelengths of a few km. Both the lower frequency limit of the extent of the "precursors" and the upper frequency limit of the scalogram spikes suggest that the mean spacing of the bubbles in Figure 8 is typically on the order of magnitude of 1 km.…”

“…This article is a companion to Bennett (2023), that describes a novel method for the observation and analysis of the roots of equatorial plasma bubbles (EPBs). Most of the details in Bennett (2023) will not be repeated here, but a brief summary is presented in the following Section 2.…”

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This article is a companion to Bennett (2023), that describes a novel method for the observation and analysis of the roots of equatorial plasma bubbles (EPBs). Most of the details in Bennett (2023) will not be repeated here, but a brief summary is presented in the following Section 2.EPBs are localized density depletions (sometimes by over four orders of magnitude relative to the surrounding plasma) in the nighttime equatorial ionosphere (Heelis, 2004;Kil & Heelis, 1998;Woodman & Hoz, 1976).

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“…The remainder of this paper is organized as follows: Section 2 provides a summary of the earlier (Bennett, 2023) paper involving the detailed description of the data sources and analysis methods relevant to the current work. The main new results in the current work involve the detailed wavevector analysis of both dispersed (i.e., whistlers) and unusually low dispersion waves.…”