Response of Mars's Topside Ionosphere to Changing Solar Activity and Comparisons to Venus

Hensley, Kerry; Withers, Paul

doi:10.1029/2020ja028913

Cited by 5 publications

(12 citation statements)

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“…These results bear similarities to those of Hensley and Withers (2021). In their study of 415 electron density profiles between 76° and 78° SZA, they found that the ratio of electron densities from high to low solar irradiance was roughly constant between 135 and 165 km.…”

Section: Datasupporting

confidence: 90%

“…The changes seen in the photochemically controlled region of a planetary ionosphere during periods of increased solar irradiance represent the combined effects of changes in the spectrum of the incident solar radiation, the neutral atmosphere (including composition and temperature), and the electron temperature. Previous work (e.g., Hensley & Withers, 2021) has shown that the influence of the electron temperature is negligible, and analysis of the electron temperatures at Mars reveals a weak dependence on solar irradiance (e.g., at 165 km, a doubling of the incident solar irradiance leads to a 26% increase in the electron temperature; Marcin Pilinski, pers. comm.…”

Section: Interpretation Of Modeling Resultsmentioning

confidence: 99%

“…The observed trends in electron density were reproduced at Venus by Hensley et al. (2020) and at Mars by Hensley and Withers (2021) using photochemical models. They found that these behaviors are controlled by changes in the O/CO 2 ratio of the neutral atmosphere with solar irradiance.…”

Section: Introductionmentioning

confidence: 81%

“…These data are augmented by a proxy for time‐varying solar ionizing irradiance. Following Hensley and Withers (2021), we use values of the Sun's flux at the radio wavelength of 10.7 cm, F 10.7 . Specifically, we use an averaged flux value, F 10.7 P , shifted in date and heliocentric distance from Earth to Mars.…”

Section: Datamentioning

confidence: 99%

“…Many previous studies (e.g., Breus et al., 2004; Fox & Yeager, 2009; Zou et al., 2006) have quantified how electron density values at the ionospheric peak increase with increasing ionizing irradiance. Hensley and Withers (2021) extended such analyses to altitudes above the ionospheric peak in the upper regions of the photochemical ionosphere. Using a set of 415 electron density profiles acquired by the MGS radio occultation experiment at solar zenith angles between 76° and 78° at local solar times around dawn, they found that changes in electron density with solar irradiance were uniform between 135 and 160 km altitude.…”

Section: Introductionmentioning

confidence: 99%

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Composition of Mars's Dayside Ionosphere Under Changing Solar Irradiance Conditions

2022

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The response of the Mars ionosphere to changes in solar irradiance is an important aspect of how conditions on Mars are shaped by our dynamic Sun. Changes in the composition of ionospheric plasma with changes in solar irradiance will affect how the ionosphere mediates the interaction of the neutral atmosphere with the surrounding space environment. Here we use MAVEN ion and neutral density measurements acquired at low (Deep Dip 8) and high (Deep Dip 2) solar irradiance conditions to determine how ion and neutral densities change when the ionizing solar irradiance doubles. We find that the neutral composition does not change significantly when examined at fixed total neutral number density. Furthermore, we find that normalCnormalO2+ ${\mathrm{C}\mathrm{O}}_{2}^{+}$ and O+ densities increase by a factor of 2, but O2+ ${\mathrm{O}}_{2}^{+}$ densities increase by a factor of 1.5. The relative abundance of O2+ ${\mathrm{O}}_{2}^{+}$ decreases as solar irradiance increases. These results are explained by straightforward theoretical considerations of changes in ion production and loss rates. However, a photochemical model fails to reproduce these results with its default set of inputs. Consistent with previous modeling efforts, normalCnormalO2+ ${\mathrm{C}\mathrm{O}}_{2}^{+}$ densities are over‐predicted. Acceptable model–data agreement requires significant adjustments to important model inputs, such as reduction in irradiance by 15%, reduction in CO2 density by a factor of 2, and increase in O density by a factor of 2. These large adjustments are suggestive of the need for improvements to the state of Mars ionosphere models based on MAVEN inputs rather than issues with the underlying data.

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Section: Datasupporting

confidence: 90%

Section: Interpretation Of Modeling Resultsmentioning

confidence: 99%