Longitudinal structures in Mars' upper atmosphere as observed by MAVEN/NGIMS

Abstract

Here we report the first comprehensive study of longitudinal structures in Mars' neutral upper atmosphere associated with atmospheric tides in composition, density and temperature using the Mars Atmosphere and Volatile Evolution Mission/Neutral Gas Ion Mass Spectrometer observations during 2015. These are in situ measurements of number densities of atmospheric species (including CO2, Ar, N2, and CO) in the altitude range from 120 to 200 km above the areoid (corresponding to a total density range from ~108–1011 cm−3), providing a data set that is larger than all previous measurements of these waves combined. These observations span from ±70° latitude and cover a wide range of local times and solar longitudes (Ls), allowing for the study of longitudinal structures under various conditions. Furthermore, the data in May and November 2015 are at similar latitudes and local times but different Ls (~340° in May, close to northern spring equinox, and 70° in November, close to northern summer solstice and aphelion), ideal for studying the seasonal effects of tides. Our analysis shows that in each month the Ar density varies with longitude having a large wave structure. It is dominated by wave 2 and 3, accounting for 8–16% of the change of the mean density. Comparison shows that the longitudinal structures at a constant CO2 density level have different amplitudes at different seasons, although their patterns are similar. The temperature structure has a phase difference from the density variation, indicating the dissipation of tides in this altitude region. The longitudinal structure is seen in all species, including major and minor species, consistent with the tidal signatures.

Martian mesospheric cloud observations by IUVS on MAVEN: Thermal tides coupled to the upper atmosphere

“…Based upon previous observations and model results [e.g., Bougher et al, ; Forbes et al, ; Withers et al, ; Kleinböhl et al, ; Moudden and Forbes , ; Medvedev et al , ; Liu et al, ], it is plausible to expect that the temperature perturbations affecting the mesosphere propagate to the upper atmosphere. IUVS measures the scale heights in the upper atmosphere from radiance profiles of the CO 2 + Ultraviolet Doublet [ Lo et al, ], which are diagnostic of temperature variations between 150 and 180 km [ Bougher et al, ].…”

“…A fit using equation reveals that wave 3 is the strongest component (5%), followed by wave 2 (4%), and wave 1 (3%). The wave 3 contribution is therefore prominent in both the thermosphere [ Liu et al, ] and mesosphere. We expect the relative contributions of these components to vary with LT and latitude [ England et al, ].…”

Seminal Evidence of a 2.5‐Sol Ultra‐Fast Kelvin Wave in Mars' Middle and Upper Atmosphere

“…These atmospheric waves transport momentum and energy from the lower atmosphere to the middle and upper atmosphere, where they are a primary driver of sol-to-sol, intraseasonal, and seasonal variability. Evidence for wave coupling into the upper atmosphere of Mars was previously diagnosed in atmospheric density measurements in the 100to 150-km region derived from accelerometer data (e.g., Moudden & Forbes, 2015;Wang et al, 2006;Withers et al, 2003), numerical modeling studies (e.g., Angelats i Coll et al, 2004;Forbes et al, 2002;Moudden & Forbes, 2008), Mars Global Surveyor radio occultation data (e.g., Cahoy et al, 2006), and Mars Atmosphere and Volatile EvolutioN (MAVEN) measurements (e.g., England et al, 2016;Liu et al, 2017).…”

Mars Thermospheric Variability Revealed by MAVEN EUVM Solar Occultations: Structure at Aphelion and Perihelion and Response to EUV Forcing

“…In addition to EUV radiation, other factors, including energy transport from global circulation and upward propagating atmospheric waves, contribute to the thermospheric thermal balance (Bougher et al, 2000(Bougher et al, , 2009Medvedev et al, 2011Medvedev et al, , 2015. These factors can result in seemingly random fluctuations in thermospheric temperature and density, as can occur from gravity waves (e.g., Yiğit, England, et al, 2015) or quasi-periodic fluctuations as can occur from atmospheric tides (e.g., Liu et al, 2017;Lo et al, 2015), or more gradual variations as can occur from large-scale circulation patterns occurring in the Mars upper atmosphere (e.g., Bougher et al, 2006). CO 2 15-μm radiative cooling is significant in the lower thermosphere, near the EUV absorption peak, but is believed to be a secondary cooling mechanism, locally, in the middle and upper thermosphere (Bougher et al, 1999;Medvedev et al, 2015).…”