The MAVEN EUVM model of solar spectral irradiance variability at Mars: Algorithms and results

Thiemann, E.; Chamberlin, Phillip C.; Eparvier, F.; Templeman, B.; Woods, Thomas N.; Bougher, S. W.; Jakosky, B. M.

doi:10.1002/2016ja023512

Cited by 140 publications

(184 citation statements)

References 51 publications

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“…The echelle observations shown here were made during the declining activity phase of Solar Cycle 24, when the Sun was less active at its maximum than in previous cycles. The solar Lyman α flux at Mars, measured by the MAVEN Extreme Ultraviolet Monitor (EUVM) instrument Lyman α channel (Eparvier et al, ), decreased by ~25%, during the mission observations shown here, when compared with consecutive times in Mars's orbit at similar L s (Thiemann et al, ).…”

Section: Resultsmentioning

confidence: 72%

The Variability of Atmospheric Deuterium Brightness at Mars: Evidence for Seasonal Dependence

et al. 2017

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The enhanced ratio of deuterium to hydrogen on Mars has been widely interpreted as indicating the loss of a large column of water into space, and the hydrogen content of the upper atmosphere is now known to be highly variable. The variation in the properties of both deuterium and hydrogen in the upper atmosphere of Mars is indicative of the dynamical processes that produce these species and propagate them to altitudes where they can escape the planet. Understanding the seasonal variability of D is key to understanding the variability of the escape rate of water from Mars. Data from a 15 month observing campaign, made by the Mars Atmosphere and Volatile Evolution Imaging Ultraviolet Spectrograph high‐resolution echelle channel, are used to determine the brightness of deuterium as observed at the limb of Mars. The D emission is highly variable, with a peak in brightness just after southern summer solstice. The trends of D brightness are examined against extrinsic as well as intrinsic sources. It is found that the fluctuations in deuterium brightness in the upper atmosphere of Mars (up to 400 km), corrected for periodic solar variations, vary on timescales that are similar to those of water vapor fluctuations lower in the atmosphere (20–80 km). The observed variability in deuterium may be attributed to seasonal factors such as regional dust storm activity and subsequent circulation lower in the atmosphere.

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Section: Resultsmentioning

confidence: 72%

The Variability of Atmospheric Deuterium Brightness at Mars: Evidence for Seasonal Dependence

et al. 2017

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“…The given flare classification is the magnitude irradiance increase in the NOAA GOES X-Ray Sensor (XRS) channel B instrument [Bornmann et al, 1996[Bornmann et al, , 1996. For the cases when the flare was only observed by MAVEN, a scaling is used that converts EUVM-B irradiance measurements to GOES XRS-B values that are determined from a set of flares when both instruments made simultaneous observations (Thiemann et al, 2017 ). Similarly, the reported flare peak time is the peak of the GOES XRS-B, when available, or the peak of the EUVM-B measurements.…”

Section: Overview Of the Mission-long Observationsmentioning

confidence: 99%

“…Such a comprehensive set of observations at Mars will allow the better characterization of the local EUV and solar wind conditions during active space weather periods and analysis of the response of the Martian system to the upstream disturbances. Some of the Mars-impacting space weather events observed by MAVEN include the heating of the neutral atmosphere triggered by large flares [Thiemann et al, 2017], the perturbation of the Martian system and ion escape enhancements due to the passage and interaction of an interplanetary coronal mass ejection (ICME) , and the triggering of diffuse auroral emission in the lower Martian atmosphere due to the precipitation of electrons during a SEP event [Schneider et al, 2015].…”

Section: Introductionmentioning

confidence: 99%

MAVEN observations of the solar cycle 24 space weather conditions at Mars

et al. 2017

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The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has been continuously observing the variability of solar soft X‐rays and EUV irradiance, monitoring the upstream solar wind and interplanetary magnetic field conditions and measuring the fluxes of solar energetic ions and electrons since its arrival to Mars. In this paper, we provide a comprehensive overview of the space weather events observed during the first ∼1.9 years of the science mission, which includes the description of the solar and heliospheric sources of the space weather activity. To illustrate the variety of upstream conditions observed, we characterize a subset of the event periods by describing the Sun‐to‐Mars details using observations from the MAVEN solar Extreme Ultraviolet Monitor, solar energetic particle (SEP) instrument, Solar Wind Ion Analyzer, and Magnetometer together with solar observations using near‐Earth assets and numerical solar wind simulation results from the Wang‐Sheeley‐Arge‐Enlil model for some global context of the event periods. The subset of events includes an extensive period of intense SEP electron particle fluxes triggered by a series of solar flares and coronal mass ejection (CME) activity in December 2014, the impact by a succession of interplanetary CMEs and their associated SEPs in March 2015, and the passage of a strong corotating interaction region (CIR) and arrival of the CIR shock‐accelerated energetic particles in June 2015. However, in the context of the weaker heliospheric conditions observed throughout solar cycle 24, these events were moderate in comparison to the stronger storms observed previously at Mars.

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“…From a preliminary examination of hundreds of orbits, Xu et al (2017) found that such nightside precipitations of photoelectrons are quite common. A convolution of a typical solar moderate EUV spectrum measured by the MAVEN Extreme Ultraviolet Monitor (Eparvier et al, 2015;Thiemann et al, 2017) with the transmission rate at the various wavelengths between 10 and 89 nm has been made, 89 nm being the longest wavelength which can still ionize CO 2 . Temperature-independent photoabsorption cross sections for N 2 , CO, Ar, and O were taken from the PHIDRATES database (https://phidrates.space.…”

Section: 1029/2018ja026336mentioning

confidence: 99%

Dawn/Dusk Asymmetry of the Martian UltraViolet Terminator Observed Through Suprathermal Electron Depletions

et al. 2019

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Suprathermal electron depletions are structures of the nightside ionosphere of Mars resulting from an equilibrium between electron loss and creation processes. Photoionization of oxygen and carbon dioxide by UV and EUV photons is the main ionization process of the Martian atmosphere. The observation of suprathermal electron depletions is strongly unexpected in the portion of the Martian environment where photoionization can occur. This region is delimited by the UltraViolet (UV) terminator, behind which no UV ionizing photons are detected. In this study suprathermal electron depletions are used to determine the position of the UV terminator thanks to MAVEN observations. The MAVEN spacecraft is now in its fourth year of data recording and has already covered more than one Martian year, a large range of latitude, local time, and solar zenith angle in the nightside down to 110‐km altitude. This coverage enables us to determine the approximate position of the UV terminator over one Martian year. We then investigate the variation of its position on the dawnside and duskside and depending on seasons. Our results are compared with models of the Martian atmosphere and in situ data of the atmospheric composition which all highlight an asymmetry between the duskside and the dawnside at equinox. However, models show an inversion in the position of the dusk and the dawn UV terminator at perihelion and aphelion, which cannot yet be confirmed or disproved by the data.

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The MAVEN EUVM model of solar spectral irradiance variability at Mars: Algorithms and results

Cited by 140 publications

References 51 publications

The Variability of Atmospheric Deuterium Brightness at Mars: Evidence for Seasonal Dependence

The Variability of Atmospheric Deuterium Brightness at Mars: Evidence for Seasonal Dependence

MAVEN observations of the solar cycle 24 space weather conditions at Mars

Dawn/Dusk Asymmetry of the Martian UltraViolet Terminator Observed Through Suprathermal Electron Depletions

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