CO2 densities and temperatures from MAVEN/IUVS between 80-150 km: Simultaneously probing the middle and upper atmosphere
Abstract
Dayglow observations of Mars' thermosphere made by the Imaging Ultraviolet Spectrograph (IUVS) aboard the MAVEN spacecraft show considerable variability over short time scales, which can't be explained solely by solar extreme ultraviolet (EUV, 10-120 nm) forcing. These thermospheric variations are indicative of strong dynamical coupling between the upper and lower atmosphere. Sandwiched between the lower and upper atmosphere, the middle atmosphere is an important system in the Martian atmosphere with observations showing the presence of strong global scale thermal tides along with smaller scale gravity waves. Ultraviolet emission from OI 297.2 nm and the CO2+ Ultraviolet Doublet (UVD) near 289 nm can together be used to retrieve CO2 densities and temperatures between 80 and 150 km. Use of O 297.2 nm emission to retrieve mesospheric CO2 densities has never been done before, because previous measurements of this emission at lower altitudes (< 100 km) were contaminated by the solar straylight. The OI 297.2 nm radiance profile exhibits a double peak; the upper emission peak (near 120 km) is produced by solar EUV photons, whereas the lower emission peak (near 85 km) is produced solely by solar Lyman α photons (121.6 nm). The relatively simple production mechanism of the lower peak, and a quantitative analysis of the IUVS limb spectra enabled for the first time by careful removal of the relatively bright solar scattered background, allows for the retrieval of CO2 densities, pressure, and temperature down to ~80 km. We analyze the observed oscillations of density and temperatureto provide the first simultaneous measurements of tides in the thermosphere (~100-200 km) and mesosphere (~80-100 km) of Mars. Our preliminary study shows strong presence of non-migrating tides in both the mesosphere and thermosphere during aphelion, but weaker (in the mesosphere) and negligible (in the thermosphere) tidal amplitudes during perihelion. This difference could be due to the stronger solar forcing during perihelion, which dominates the temperature structure. By simultaneously measuring the temperatures and densities in the middle and upper atmospheres of Mars, our analysis quantifies the role of lower atmosphere coupling in the observed temperature variability and its implication for mesospheric physics (such as cloud formation).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P43A..06J
- Keywords:
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- 0343 Planetary atmospheres;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 6225 Mars;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 5405 Atmospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5445 Meteorology;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS