Characterization of the lower layer in the dayside Venus ionosphere and comparisons with Mars

Girazian, Zachary; Withers, Paul; Häusler, B.; Pätzold, M.; Tellmann, S.; Peter, Kerstin

doi:10.1016/j.pss.2015.06.007

Cited by 20 publications

(28 citation statements)

References 49 publications

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“…We first linearize

N_{e} = N_{0} F_{10.7 P}^{k}

and rewrite it as

\ln N_{e} = \ln N_{0} + k \ln F_{10.7 P}

. We follow the fitting technique outlined in Girazian et al (), in which the measurement uncertainty for each electron density profile, which is far smaller than the scatter in the data, provides the relative uncertainty for the least squares fitting. The overall magnitude of the error is then allowed to increase until the chi‐square value equals one.…”

Section: Analysis Of Vex Datamentioning

confidence: 99%

“…The sharp increase in k at altitudes below 130 km reflects the increased importance of electron‐impact ionization below the main peak. The Sun's X‐ray flux exhibits more variation from low to high solar activity than longer wavelengths (Girazian et al, ). Based on the

F_{10.7 P}

‐averaged model of the solar spectrum used in this work (see section and figures therein), the solar photon flux increases by roughly 70% at 90 nm (the threshold wavelength for ionization of CO

_{2}

) from

F_{10.7 P}

= 65 sfu to

F_{10.7 P}

= 155 sfu, while the flux at 10 nm increases by more than 300% over the same solar activity range.…”

Section: Analysis Of Vex Datamentioning

confidence: 99%

“…The characteristics of an ionosphere are largely determined by the planet's surface gravity, neutral atmospheric composition, orbital distance, rotation rate, and magnetic field (Schunk & Nagy, ). The spectrum of the incident ionizing radiation also has a significant impact on the vertical structure of a planetary ionosphere (e.g., Girazian et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…The effect of solar cycle variations on the V2 peak, the V1 peak, and the ionopause has been explored using in situ and remote sensing data by Kliore and Mullen (), Girazian et al (), and Phillips et al (), respectively, but the PCE region above the main ionospheric peak exhibits interesting behavior as well. Taylor et al () analyzed in situ measurements of O

^{+}

, O

_{2}^{+}

, C

^{+}

, and CO

_{2}^{+}

densities between the altitudes of 180 and 220 km and found that the densities of these ions were correlated with the Sun's flux at a wavelength of 10.7 cm, indicating that solar activity has a discernible impact on the conditions in the dayside ionosphere at these altitudes.…”

Section: Introductionmentioning

confidence: 99%

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Dependence of Dayside Electron Densities at Venus on Solar Irradiance

et al. 2020

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The ionosphere of Venus is a weakly ionized plasma layer embedded in the planet's upper atmosphere. Planetary ionospheres provide an excellent opportunity to study how our variable Sun affects the planets in our solar system. Because ionospheres are reservoirs from which atmospheric species can be lost to space, studying how ionospheres respond to changes in solar activity can help us understand how planetary atmospheres have evolved since their formation. While variations of the main and lower ionospheric peaks of Venus have been well studied, the behavior of the ionosphere above the altitude of the greatest electron density has not been fully constrained. To investigate the behavior of this region, we use electron density profiles obtained by the Venus Radio Science experiment aboard Venus Express. An increase in the response of the electron density to increasing solar irradiance with increasing altitude above the peak is readily apparent in these data. By using a one‐dimensional photochemical equilibrium model to investigate the factors that drive the variations of the ionosphere of Venus, we find that changes in the composition of the underlying neutral atmosphere are responsible for the observed increase in ionospheric response with altitude.

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“…We first linearize

N_{e} = N_{0} F_{10.7 P}^{k}

and rewrite it as

\ln N_{e} = \ln N_{0} + k \ln F_{10.7 P}

Section: Analysis Of Vex Datamentioning

confidence: 99%

F_{10.7 P}

‐averaged model of the solar spectrum used in this work (see section and figures therein), the solar photon flux increases by roughly 70% at 90 nm (the threshold wavelength for ionization of CO

_{2}

) from

F_{10.7 P}

= 65 sfu to

F_{10.7 P}

= 155 sfu, while the flux at 10 nm increases by more than 300% over the same solar activity range.…”

Section: Analysis Of Vex Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

^{+}

, O

_{2}^{+}

, C

^{+}

, and CO

_{2}^{+}

Section: Introductionmentioning

confidence: 99%

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Dependence of Dayside Electron Densities at Venus on Solar Irradiance

et al. 2020

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“…Figure 28 shows exemplarily the general structure of a quiet Venus ionospheric electron density distribution. The two-layer structure of the lower ionosphere with the lower "V1" 1 layer at an radius of 6180 km 2 (altitude of 130 km) and the main "V2" layer at a radius of 6190 km (altitude 140 km) is prominent (Pätzold et al 2007;Girazian et al 2015). This specific electron density profile was observed on DOY017, 2008, by the Venus Express 1 Other researchers call the lower and the main layer E and F1 layer, respectively, in order to compare with similar formations in the Earth ionosphere (e.g.…”

Section: The Venus Ionosphere In the Pre-vex Eramentioning

confidence: 99%

Aeronomy of the Venus Upper Atmosphere

et al. 2017

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We present aeronomical observations collected using remote sensing instruments on board Venus Express, complemented with ground-based observations and numerical modeling. They are mostly based on VIRTIS and SPICAV measurements of airglow obtained in the nadir mode and at the limb above 90 km. They complement our understanding of the behavior of Venus' upper atmosphere that was largely based on Pioneer Venus observations mostly performed over thirty years earlier. Following a summary of recent spectral data from the EUV to the infrared, we examine how these observations have improved our knowledge of the composition, thermal structure, dynamics and transport of the Venus upper atmosphere. We then synthesize progress in three-dimensional modeling of the upper atmosphere which is largely based on global mapping and observations of time variations of the nitric oxide and O 2 nightglow emissions. Processes controlling the escape flux of atoms to space are described. Results based on the VeRA radio propagation experiment are summarized and compared to ionospheric measurements collected during earlier space missions. Finally, we point out some unsolved and open questions generated by these recent datasets and model comparisons.

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An empirical model of the extreme ultraviolet solar spectrum as a function of F_10.7

Girazian

Withers

2015

JGR Space Physics

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The F10.7 solar index is frequently used as a proxy for the solar extreme ultraviolet (EUV) irradiance. However, the relationship between F10.7 and the EUV spectrum has not been quantified in great detail for Solar Cycles 23 and 24. We use more than 2800 spectra (2003–2010) from the Solar EUV Experiment (SEE) to construct an empirical model of the EUV spectrum as a function of F10.7P = 12(F10.7+F10.7A) where F10.7A is the 81 day average. We compare our spectra to the HEUVAC model and find the HEUVAC soft X‐ray irradiance is ∼65% larger than SEE during solar minimum and HEUVAC H Lymann continuum fluxes are ∼30% smaller. We derive power law relationships between F10.7P and the ionizing irradiance—the integrated flux within some EUV wavelength band—in units of energy flux (FE) and photon flux (FP) for five neutral species and show that the relationship between F10.7P and FE is more linear than that of FP and that the magnitude of FP and its solar cycle variation is species dependent. In addition, we derive power law relationships between F10.7P and the ionization frequencies of these species and confirm that F10.7P is a better EUV proxy than F10.7. Finally, we investigate the hardening of the spectrum and its consequences for the Venus, Earth, and Mars ionospheres; the ratio of the soft X‐ray to EUV irradiance appropriate for Earth's E and F layers stayed constant during the prolonged solar minimum. Our results can elucidate ionospheric processes such as the saturation effect.

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Characterization of the lower layer in the dayside Venus ionosphere and comparisons with Mars

Cited by 20 publications

References 49 publications

Dependence of Dayside Electron Densities at Venus on Solar Irradiance

Dependence of Dayside Electron Densities at Venus on Solar Irradiance

Aeronomy of the Venus Upper Atmosphere

An empirical model of the extreme ultraviolet solar spectrum as a function of F_10.7

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Characterization of the lower layer in the dayside Venus ionosphere and comparisons with Mars

Cited by 20 publications

References 49 publications

Dependence of Dayside Electron Densities at Venus on Solar Irradiance

Dependence of Dayside Electron Densities at Venus on Solar Irradiance

Aeronomy of the Venus Upper Atmosphere

An empirical model of the extreme ultraviolet solar spectrum as a function of F10.7

Contact Info

Product

Resources

About

An empirical model of the extreme ultraviolet solar spectrum as a function of F_10.7