Dynamical Heating in the Martian Thermosphere.

Autor: Pilinski, M. D.1 (AUTHOR) Marcin.Pilinski@lasp.colorado.edu, Roeten, K. J.2 (AUTHOR), Bougher, S. W.2 (AUTHOR), Benna, M.3,4 (AUTHOR)
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Zdroj: Journal of Geophysical Research. Planets. Jun2023, Vol. 128 Issue 6, p1-18. 18p.
Abstrakt: Dynamical heating and cooling are prominent features of planetary atmospheres resulting in thermospheric structures on Venus, Earth and Mars. The purpose of this study is to determine the location and amplitude of localized heating regions in the Martian thermosphere, confirm that they occur in regions of wind convergence and compare the observed dynamical heating with that predicted by a global thermospheric model. This investigation uses several years of data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission including observations made by the Neutral Gas and Ion Mass Spectrometer (NGIMS) as well as the Extreme Ultraviolet Monitor (EUVM). Specifically, the analysis focuses on several years of horizontal wind, temperature, and composition data. EUVM measurements provide a solar forcing context for the neutral thermosphere data sets and aid in the statistical analysis. Statistical results are compared with two versions of the Mars Global Ionosphere Thermosphere (M‐GITM) global circulation model: one that includes gravity wave parametrization and a version without gravity wave effects. Data analysis indicates that heating features exist around 2–3 and 17–18 local solar time. These locations coincide with regions of converging winds and are in better agreement with M‐GITM when a gravity wave parametrization is included in the model. An oscillation in the observed wind field also results in convergence and a density enhancement near 15 local time. While a similar oscillation is reproduced by the model, the amplitude is much lower than observed and may be a result of modeled zonal winds that are too low. Plain Language Summary: The upper reaches of planetary atmospheres act as the interface between the planet and the interplanetary space environment. On Mars, this region is responsible for aerodynamic drag on satellites orbiting the planet. It is also part of the pathway for molecules escaping to space and contributing to the loss of most of the Martian atmosphere and water over the course of billions of years. The motion and structure of the upper atmospheric region are important to understanding and predicting its behavior. We analyzed wind and temperature data collected in the upper atmosphere of Mars by a NASA satellite called the Mars Atmosphere and Volatile EvolutioN spacecraft and compared the results to a model of the Mars atmosphere. The results indicate that locations of converging and diverging winds exist throughout the atmosphere and contribute to its temperature and density structure. These locations of converging winds cause hot spots in the upper atmosphere, particularly on the night side. The wind pattern is also responsible for the presence of large ripples or wave‐like features in the dayside atmosphere. Key Points: Equinox analysis confirms the presence of dynamical heating post‐midnight and near the dusk terminatorIncluding gravity wave parametrization in the Mars Global Ionosphere Thermosphere Model improves the specification of dynamical heatingA global modulation of the thermospheric wind pattern leads to an oscillation in dynamical effects with a 4‐hr local time wavelength [ABSTRACT FROM AUTHOR]
Databáze: GreenFILE
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