Numerical simulations of the influence of solar zenith angle on properties of the M1 layer of the Mars ionosphere

Fallows, K.; Withers, Paul; Matta, Majd

doi:10.1002/2014ja020947

Cited by 11 publications

(22 citation statements)

References 45 publications

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“…The analysis was later extended by Mendillo et al () to incorporate as many as 215,818 peak electron density values from the years 2005–2015. Sánchez‐Cano et al () used the same parametrization and a combined data set of 1,200 MARSIS radar sounding profiles and 500 Mars Global Surveyor occultation profiles to construct a model of electron densities describing not only the main M2 ionospheric layer but also the lower M1 layer (Fallows et al, , ; Fox & Weber, ; Fox & Yeager, ). Němec et al () used 30,283 MARSIS radar sounding profiles and almost 200,000 local electron density measurements to develop an empirical model of electron densities above the peak altitude, which assumes a Chapman dependence at altitudes below about 200 km (photochemically controlled region) and smoothly transits to an exponential dependence at altitudes above about 325 km (diffusion‐controlled region).…”

Section: Introductionmentioning

confidence: 99%

Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere

et al. 2019

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We use more than 10 years of the Martian topside ionospheric data measured by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft to derive an empirical model of electron densities from the peak altitude up to 325 km. Altogether, 16,044 electron density profiles obtained at spacecraft altitudes lower than 425 km and at solar zenith angles lower than 80° are included in the analysis. Each of the measured electron density profiles is accurately characterized by the peak electron density, peak altitude, and three additional parameters describing the profile shape above the peak: (i) steepness at high altitudes, (ii) main layer thickness, and (iii) transition altitude. The dependence of these parameters on relevant controlling factors (solar zenith angle, solar irradiance, crustal magnetic field magnitude, and Sun‐Mars distance) is evaluated, allowing for a formulation of a simple empirical model. Mars Atmosphere and Volatile EvolutioN Extreme Ultraviolet monitor data are used to show that the solar ionizing flux can be accurately approximated by the F10.7 index when taking into account the solar rotation. Electron densities predicted by the resulting empirical model are compared with electron densities locally evaluated based on the Mars Advanced Radar for Subsurface and Ionosphere Sounding measurements, with the Langmuir Probe and Waves electron density measurements on board the Mars Atmosphere and Volatile EvolutioN spacecraft, and with electron densities obtained by radio occultation measurements. Although the electron densities measured by the Langmuir Probe and Waves instrument are systematically somewhat lower than the model electron densities, consistent with former findings, the model performs reasonably well.

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Section: Introductionmentioning

confidence: 99%

Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere

et al. 2019

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“…In addition, electron impact ionization (EII) from photoelectrons becomes more important below the main (M2) peak (Withers, 2009). Simulating EII can be achieved by employing either an electron transport model (e.g., Fox & Dalgarno, 1979) or a wavelength-dependent yield function to represent Geophysical Research Letters 10.1029/2018GL078524 multiple ion-electron pairs being created by a single photon (e.g., Bougher et al, 2001;Fallows et al, 2015a;Haider et al, 2012;Lollo et al, 2012;Mendillo et al, 2006). Solar EUV and X-ray fluxes vary strongly with solar activity.…”

Section: Introductionmentioning

confidence: 99%

Observations and Modeling of the Mars Low‐Altitude Ionospheric Response to the 10 September 2017 X‐Class Solar Flare

Thiemann

Mitchell

et al. 2018

Geophysical Research Letters

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Solar extreme ultraviolet and X‐ray photons are the main sources of ionization in the Martian ionosphere and can be enhanced significantly during a solar flare. On 10 September 2017, the Mars Atmosphere and Volatile EvolutioN orbiter observed an X8.2 solar flare, the largest it has encountered to date. Here we investigate the ionospheric response before, during, and after this event with the SuperThermal Electron Transport model. We find good agreement between modeled and measured photoelectron spectra. In addition, the high photoelectron fluxes during the flare provide adequate statistics to allow us to clearly and repeatedly identify the carbon Auger peak in the ionospheric photoelectron energy spectra at Mars for the first time. By applying photochemical equilibrium, O 2+ and CO 2+ densities are obtained and compared with Mars Atmosphere and Volatile EvolutioN observations. The variations in ion densities during this event due to the solar irradiance enhancement and the neutral atmosphere expansion are discussed.

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“…The rates of several geophysically important processes, such as the escape of energetic oxygen atoms produced by dissociative recombination of O 2 + , depend strongly on the plasma electron temperature (e.g., Andersson et al, 2010;Brecht et al, 2017;Ergun et al, 2016;Fox & Hac, 2009;Lillis et al, 2015, and others). Attempts to reconcile the Viking electron temperature profiles with models of the ionosphere required reasonable but unverified assumptions (e.g., Cui et al, 2015;Fallows et al, 2015aFallows et al, , 2015bFox & Yeager, 2006;Matta et al, 2014;Withers et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Martian Electron Temperatures in the Subsolar Region: MAVEN Observations Compared to a One‐Dimensional Model

et al. 2018

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Prior to the Mars Atmospheric Volatile EvolutioN (MAVEN) mission, altitude profiles of the electron temperature in the Martian thermosphere were measured only twice. Because the rates of several geophysically important processes depend strongly on the electron temperature, models of the Martian thermosphere and atmospheric escape rates have not been well constrained. In this paper, we use densities and temperatures measured by MAVEN instruments and the one‐dimensional model of Matta et al. (2014, https://doi.org/10.1016/j.icarus.2013.09.006) to test our understanding of the processes that determine the electron temperature. Our analysis is limited to inbound orbits where the magnetic field is within 30° of horizontal and the satellite is within 30° of the subsolar point at altitudes from 120 to 250 km. We introduce empirically adjusted electron temperatures below 180 km, where the MAVEN electron temperature measurements are known to be biased high. We introduce the concept of a local electron heating efficiency, which we define at a given altitude as the ratio of electron heating from photoionization to the total extreme ultraviolet energy deposited. Our analysis shows that MAVEN observations are consistent with the one‐dimensional model below ~210 km if the electron heating efficiency varies with altitude, and the electron temperature is within the empirical bounds below 180 km we introduced. It indicates that above ~210 km electron heat conduction dominates extreme ultraviolet heating in determining electron temperature. Our analysis also suggests that in the subsolar region electrons and neutrals are in thermal equilibrium below 120 km.

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Numerical simulations of the influence of solar zenith angle on properties of the M1 layer of the Mars ionosphere

Cited by 11 publications

References 45 publications

Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere

Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere

Observations and Modeling of the Mars Low‐Altitude Ionospheric Response to the 10 September 2017 X‐Class Solar Flare

Martian Electron Temperatures in the Subsolar Region: MAVEN Observations Compared to a One‐Dimensional Model

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