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Communication Dans Un Congrès Année : 2019

Seasonal and Diurnal Variation in Vertical Profiles of the Martian Nitric Oxide Nightglow Layer

Résumé

The nitric oxide (NO) nightglow is a reaction rate which traces flux between from the nightside Martian thermosphere to the mesosphere. The process begins in the dayside thermosphere, where solar extreme ultraviolet radiation photo-dissociates atmospheric CO2and N2molecules. Upper-atmosphere Hadley circulation transports N and O atoms toward the nightside poles, where descending polar winds bring the atoms down into the mesosphere. The atoms combine to form an excited NO molecule, which nearly-instantaneously relaxes, emitting ultraviolet photons in the distinctive NO δ and γ bands. Brighter emission occurs where descending air brings molecules deeper into the mesosphere, so we use the reaction rate as a tracer of the dynamics between Mars' thermosphere and mesosphere. We use limb scan data from the Imaging Ultraviolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile Evolution (MAVEN) mission. These data have broad seasonal and latitudinal coverage, allowing us to characterize the behavior of the nightglow layer across a range of latitudes, local times, and solar longitudes. Figure 1 shows an example of a calibrated spectrum and the NO brightness derived from it. We report observational analysis of altitude and brightness variation in the NO nightglow layer on seasonal and diurnal timescales, extending the analysis in our previous limb scan study. Using an LMD-MGCM climatology simulation of the NO nightglow, we define arbitrary "seasons" as a function of latitude and solar longitude which we use to analyze how the layer changes with season. We compute the peak altitude and brightness of the seasonal average and compare across seasons. We also compute the brightness and peak altitude of the layer as a function of local time to determine how the vertical structure of the layer changes over the course of a night. We also report comparisons of our observations to simulations from the LMD-MGCM and corresponding insights into altitude- and temporal-dependence of temperature, downwelling wind velocity, and atomic N and O densities.
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insu-04404088 , version 1 (18-01-2024)

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Z. Milby, N. M. Schneider, S. Jain, F. Gonzalez-Galindo, E. M. Royer, et al.. Seasonal and Diurnal Variation in Vertical Profiles of the Martian Nitric Oxide Nightglow Layer. American Geophysical Union, Fall Meeting 2019, Dec 2019, San Francisco (CA), United States. ⟨insu-04404088⟩
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