Imaging of Martian Circulation Patterns and Atmospheric Tides Through MAVEN/IUVS Nightglow Observations

Abstract

We report results from a study of two consecutive Martian years of imaging observations of nitric oxide ultraviolet nightglow by the Imaging Ultraviolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile Evolution (MAVEN) mission spacecraft. The emission arises from recombination of N and O atoms in Mars' nightside mesosphere. The brightness traces the reaction rate as opposed to the abundance of constituents, revealing where circulation patterns concentrate N and O and enhance recombination. Emissions are brightest around the winter poles, with equatorial regions brightening around the equinoxes. These changes offer clear evidence of circulation patterns transitioning from a single cross‐equatorial cell operating during solstice periods to more symmetric equator‐to‐poles circulation around the equinoxes. Prominent atmospheric tides intensify the emissions at different longitudes, latitude ranges, and seasons. We find a strong eastward‐propagating diurnal tide (DE2) near the equator during the equinoxes, with a remarkably bright spot narrowly confined near (0°, 0°). Wave features at the opposite winter poles are dissimilar, reflecting different circulation patterns at perihelion versus aphelion. LMD‐MGCM simulations agree with the patterns of most observed phenomena, confirming that the model captures the dominant physical processes. At the south winter pole, however, the model fails to match a strong wave‐1 spiral feature. Observed brightnesses exceed model predictions by a factor of 1.9 globally, probably due to an underestimation of the dayside production of N and O atoms. Further study of discrepancies between the model and observations offers opportunities to improve our understanding of chemical and transport processes controlling the emission.

Discrete Aurora on Mars: Insights Into Their Distribution and Activity From MAVEN/IUVS Observations

“…The observation files used in this work are identified as “periapse” version 13 of the Level 1B data available at the PDS IUVS repository under “Limb Scan … Processed Data.” The data processing methodology for nightside observations is described in detail in Schneider et al. (2020). Below we describe additional processing steps unique to this auroral study.…”

“…The instrumental fitted spectra were converted to kiloRayleighs (abbreviated kR) per nm using stellar calibration observations (Schneider et al., 2020), and then summed over the spectral feature to yield the emission brightness in kR. Random uncertainties in a pixel's fitted intensities were calculated based on the combination of photon statistics and detector background noise in the original spectrum.…”

Discrete Aurora on Mars: Spectral Properties, Vertical Profiles, and Electron Energies

“…The MUV brightness data carry an estimated systematic uncertainty of 30%. Level 1 C (L1C; Schneider et al., 2020; Schneider21) cleaned data, archived with the NASA Planetary Data System (PDS), have been used to detect auroral signatures (see Section 2.2) and quantify the auroral emissions (see Section 3).…”

Observations of Atmospheric Tides in the Middle and Upper Atmosphere of Mars From MAVEN and MRO

“…Schneider et al. (2020) identified the presence of wavenumber‐3 structure in the NO nightglow brightness derived from MAVEN‐IUVS in the middle atmosphere at low equatorial latitudes. On further examining the phase of the wave with local time, the authors found that the predominant tide underlying the wavenumber‐3 structure is the eastward moving diurnal tide with zonal wavenumber s = 2 (DE2).…”