Modeling of the lower ionospheric response and VLF signal modulation during a total solar eclipse using ionospheric chemistry and LWPC
01 Jul 2018-Vol. 42
TL;DR: In this paper, the effects of the total solar eclipse on the VLF signal were investigated using the knowledge of the lower ionospheric chemical and physical properties, which is not well studied till date.
Abstract: The variation in the solar Extreme Ultraviolet (EUV) radiation flux by any measure is the most dominant natural source to produce perturbations or modulations in the ionospheric chemical and plasma properties. A solar eclipse, though a very rare phenomenon, is similarly bound to produce a significant short time effect on the local ionospheric properties. The influence of the ionizing solar flux reduction during a solar eclipse on the lower ionosphere or, more precisely, the D-region, can be studied with the observation of Very Low Frequency (VLF) radio wave signal modulation. The interpretation of such an effect on VLF signals requires a knowledge of the D-region ion chemistry, which is not well studied till date. Dominant parameters which govern the ion chemistry, such as the recombination coefficients, are poorly known. The occurrence of events such as a solar eclipse provides us with an excellent opportunity to investigate the accuracy of our knowledge of the chemical condition in this part of Earth’s atmosphere and the properties which control the ionospheric stability under such disturbances. In this paper, using existing knowledge of the lower ionospheric chemical and physical properties we carry out an interpretation of the effects obtained during the total solar eclipse of 22 of July 2009 on the VLF signal. Data obtained from a week long campaign conducted by the Indian Centre for Space Physics (ICSP) over the Indian subcontinent has been used for this purpose. Both positive and negative amplitude changes during the eclipse were observed along various receiver locations. In this paper, data for a propagation path between a Indian Navy VLF transmitter named VTX3 and a pair of receivers in India are used. We start from the observed solar flux during the eclipse and calculate the ionization during the whole time span over most of the influenced region in a range of height. We incorporate a D-region ion-chemistry model to find the equilibrium ion density over the region and employ the LWPC code to find the VLF signal amplitude. To tackle the uncertainty in the values of the recombination coefficients we explore a range of values in the chemical evolution model. We achieve two goals by this exercise: First, we have been able to reproduce the trends, if not the exact signal variation, of the VLF signal modulations during a solar eclipse at two different receiving stations with sufficient accuracy purely from theoretical modeling, and second our knowledge of some of the D-region ion-chemistry parameters is now improved.
Citations
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TL;DR: Junge as mentioned in this paper discusses air chemistry and radioactivity, and discusses the relationship between air chemistry, radioactivity and air physics, and shows that air chemistry can be viewed as a special case of radioactivity.
Abstract: Air Chemistry and Radioactivity By Christian E. Junge. (International Geophysics Series, Vol. 4.) Pp. xii + 382. (New York: Academic Press, Inc.; London: Academic Press, Inc. (London), Ltd., 1963.) 96s. 6d.
165 citations
TL;DR: In this paper, a review of the use of very low frequency (VLF, 3-30 kHz) signals generated by various natural and man-made sources for the study of the ionospheric D-region and the mesosphere-lower thermosphere is presented.
Abstract: The ionospheric D-region (~60 km up to ~95 km) and the corresponding neutral atmosphere, often referred to as the mesosphere–lower thermosphere (MLT), are challenging and costly to probe in situ. Therefore, remote sensing techniques have been developed over the years. One of these is based on very low frequency (VLF, 3–30 kHz) electromagnetic waves generated by various natural and man-made sources. VLF waves propagate within the Earth–ionosphere waveguide and are extremely sensitive to perturbations occurring in the D-region along their propagation path. Hence, measurements of these signals serve as an inexpensive remote sensing technique for probing the lower ionosphere and the MLT region. This paper reviews the use of VLF narrowband (NB) signals (generated by man-made transmitters) in the study of the D-region and the MLT for over 90 years. The fields of research span time scales from microseconds to decadal variability and incorporate lightning-induced short-term perturbations; extraterrestrial radiation bursts; energetic particle precipitation events; solar eclipses; lower atmospheric waves penetrating into the D-region; sudden stratospheric warming events; the annual oscillation; the solar cycle; and, finally, the potential use of VLF NB measurements as an anthropogenic climate change monitoring technique.
40 citations
Cites background or result from "Modeling of the lower ionospheric r..."
...…remains widely used more than five decades since its first publication (e.g., Thomson and Clilverd 2001; McRae and Thomson 2004; Grubor et al. 2008; Chakraborty et al. 2016), being mostly embedded in computer models, e.g., the Naval Ocean Systems Center (NOSC) Long Wave Propagation Capability…...
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...Recently, Chakraborty et al. (2016) used a D-region ion chemistry model alongside the LWPC model, in order to improve the inferred ionospheric profile (and its ‘Wait’ parameters) during the passage of a TSE, which they compared to the results of Pal et al. (2012)....
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01 Sep 1974
TL;DR: In this paper, a unified picture of the chemistry of the normal and the disturbed D-region is presented under disturbed conditions, including: (a) solar flares, (b) PCAs and (c) solar eclipses.
Abstract: A unified picture of the chemistry of the normal and the disturbed D-region is presented. Under disturbed conditions we include: (a) solar flares, (b) PCAs and (c) solar eclipses. The connecting thread is the six ion model of Mitra and Rowe, with appropriate modifications where necessary. Several areas of identity in the observational results of flares and PCAs are reviewed. These include: the dominance of q(O2+) over q(NO+) due to X-rays in the first case and energetic particles in the second; drastic decrease in the effective loss coefficient during both flares and PCAs; disappearance of water cluster ions down to 73 km during day and 78 km at night during PCAs; the reversion of negative ions to their basic forms (O− and O2−) during PCAs. For solar eclipses, the effects are essentially a mirror image of these due to flares and PCAs.
28 citations
TL;DR: In this paper, the amplitude and phase variations of the sub-ionospheric Very Low Frequency (VLF) signal were measured during the total solar eclipse (TSE) in North America.
20 citations
TL;DR: In this paper, the authors used the electron density profiles based on IRI outcomes during a quiet ionospheric condition, and used the Wait's exponential model with a log-linear fitting of electron density to compute the β and h′ from their fundamental definition.
11 citations
References
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TL;DR: In this paper, the MSIS-86 empirical model has been extended into the mesosphere and lower atmosphere to provide a single analytic model for calculating temperature and density profiles representative of the climatological average for various geophysical conditions.
Abstract: The MSIS-86 empirical model has been revised in the lower thermosphere and extended into the mesosphere and lower atmosphere to provide a single analytic model for calculating temperature and density profiles representative of the climatological average for various geophysical conditions. Tabulations from the Handbook for MAP 16 are the primary guide for the lower atmosphere and are supplemented by historical rocket and incoherent scatter data in the upper mesosphere and lower thermosphere. Low-order spherical harmonics and Fourier series are used to describe the major variations throughout the atmosphere including latitude, annual, semiannual, and simplified local time and longitude variations. While month to month details cannot be completely represented, lower atmosphere temperature data are fit to an overall standard deviation of 3 K and pressure to 2%. Comparison with rocket and other data indicates that the model represents current knowledge of the climatological average reasonably well, although there is some conflict as to details near the mesopause.
2,359 citations
"Modeling of the lower ionospheric r..." refers methods in this paper
...The NASA-MSIS90 atmospheric model (Hedin 1991) is used to find neutral atom concentrations at different altitudes and temperature, required for calculations of the coefficient....
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Book•
01 Jan 2000TL;DR: The terrestrial ionosphere at middle and low latitudes and planetary ionospheres at high latitudes have been studied in this article for the first time, and the results show that the terrestrial ionosphere at low and mid-latitudes is more stable than the high-latitude ionosphere.
Abstract: 1. Introduction 2. Space environment 3. Transport equations 4. Collisions 5. Simplfied transport equations 6. Wave phenomena 7. Magnetohydrodynamic formulation 8. Chemical processes 9. Ionization and energy exchange processes 10. Neutral atmospheres 11. The terrestrial ionosphere at middle and low latitudes 12. The terrestrial ionosphere at high latitudes 13. Planetary ionospheres 14. Ionospheric measurement techniques Appendices.
981 citations
"Modeling of the lower ionospheric r..." refers background in this paper
...Various ionospheric reports and review papers (e.g., Schunk and Nagy 1980, 2000; Rees 1989; Lilensten and Blelly 1999) presented the value of dissociative recombination rate differing as much as factor of 2....
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Book•
06 Oct 2018
483 citations
"Modeling of the lower ionospheric r..." refers background or methods in this paper
...Any variation of the solar flux which could affect the electron distribution in the lower ionosphere (generally represented by Wait’s formula (Wait and Spies 1964)) is determined with two parameters, namely the effective reflection height (h′) and the conductivity gradient or sharpness parameter…...
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...According to the mode theory (Budden 1961; Wait and Spies 1964), the very low frequency signal at certain frequency at a receiver is a superposition of the electric field associated with various modes originated from the transmitter and reaching the receiver point after being reflected and attenuated within the Earth-ionosphere waveguide....
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...According to the mode theory (Budden 1961; Wait and Spies 1964), the very low frequency signal at certain frequency at a receiver is a superposition of the electric field associated with various modes originated from the transmitter and reaching the receiver point after being reflected and…...
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...Any variation of the solar flux which could affect the electron distribution in the lower ionosphere (generally represented by Wait’s formula (Wait and Spies 1964)) is determined with two parameters, namely the effective reflection height (h′) and the conductivity gradient or sharpness parameter (β), which in turn can modulate the VLF signal....
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TL;DR: In this paper, the authors show that the optical emission levels are predominantly defined by the lightning discharge duration and the conductivity properties of the atmosphere/lower ionosphere (i.e., relaxation time of electric field in the conducting medium).
Abstract: Quasi-electrostatic (QE) fields that temporarily exist at high altitudes following the sudden removal (e.g., by a lightning discharge) of thundercloud charge at low altitudes lead to ambient electron heating (up to ∼5 eV average energy), ionization of neutrals, and excitation of optical emissions in the mesosphere/lower ionosphere. Model calculations predict the possibility of significant (several orders of magnitude) modification of the lower ionospheric conductivity in the form of depletions of electron density due to dissociative attachment to O2 molecules and/or in the form of enhancements of electron density due to breakdown ionization. Results indicate that the optical emission intensities of the 1st positive band of N2 corresponding to fast (∼ 1 ms) removal of 100–300 C of thundercloud charge from 10 km altitude are in good agreement with observations of the upper part (“head” and “hair” [Sentman et al., 1995]) of the sprites. The typical region of brightest optical emission has horizontal and vertical dimensions ∼10 km, centered at altitudes 70 km and is interpreted as the head of the sprite. The model also shows the formation of low intensity glow (“hair”) above this region due to the excitation of optical emissions at altitudes ∼ 85 km during ∼ 500 μs at the initial stage of the lightning discharge. Comparison of the optical emission intensities of the 1st and 2nd positive bands of N2, Meinel and 1st negative bands of , and 1st negative band of demonstrates that the 1st positive band of N2 is the dominating optical emission in the altitude range around ∼70 km, which accounts for the observed red color of sprites, in excellent agreement with recent spectroscopic observations of sprites. Results indicate that the optical emission levels are predominantly defined by the lightning discharge duration and the conductivity properties of the atmosphere/lower ionosphere (i.e., relaxation time of electric field in the conducting medium). The model demonstrates that for low ambient conductivities the lightning discharge duration can be significantly extended with no loss in production of optical emissions. The peak intensity of optical emissions is determined primarily by the value of the removed thundercloud charge and its altitude. The preexisting inhomogeneities in the mesospheric conductivity and the neutral density may contribute to the formation of a vertically striated fine structure of sprites and explain why sprites often repeatedly occur in the same place in the sky as well as their clustering. Comparison of the model results for different types of lightning discharges indicates that positive cloud to ground discharges lead to the largest electric fields and optical emissions at ionospheric altitudes since they are associated with the removal of larger amounts of charge from higher altitudes.
434 citations
"Modeling of the lower ionospheric r..." refers background in this paper
...It consists of two parts, one is for the three body attachment process and the other is from the two body dissociation process (Pasko et al. 1997; Haldoupis et al. 2009)....
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TL;DR: In this paper, a reduced set of cross-section and flux data is presented for the wavelength range below 1027A, consisting of 37 wavelength intervals, for various dates exhibiting notably different levels of solar activity.
Abstract: Increases in the solar ultraviolet flux (wavelengths shorter than 1250A) over the past five years of rising solar activity have been larger than anticipated. This increase in UV flux dramatically affects the production of ionization of the various constituents in the thermosphere. Measurements of the solar UV flux by the Atmosphere Explorer satellites are used to determine ionization frequencies for the major thermospheric species for various dates exhibiting notably different levels of solar activity. For the convenience of users of such data, a reduced set of cross-section and flux data is presented for the wavelength range below 1027A, consisting of 37 wavelength intervals
341 citations
"Modeling of the lower ionospheric r..." refers background in this paper
...7 = 68, from Torr et al. (1979), with some values of intensities collected from the wellknown literature are documented in Turunen et al. (1992)....
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...There are several works in the literature on the absorption cross section and photo ionization efficiencies, such as Torr et al. (1979) for N2, O2 and O , Ohshio et al. (1966) for NO and Ar and Mecwan and Philips (1975) for CO2....
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