P040-03
The Martian Thermospheric Heat Islands: Dynamical Heating at Dawn and Dusk

Thursday, 10 December 2020: 20:38
Virtual
Marcin Pilinski1, Kali Roeten2, Stephen W Bougher2, Mehdi Benna3 and Laila Andersson4, (1)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (2)Climate and Space Sciences and Engineering Department, Ann Arbor, MI, United States, (3)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (4)Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, United States
Recorded Presentation
Abstract:
Dynamical heating and cooling are prominent features of planetary atmospheres manifesting in the night-time temperature of the Venus thermosphere, cooling in antibaric rotation cells in the Earth’s auroral thermosphere, and local “islands” of dynamical heating in the Martian thermosphere. On Mars, these features were first postulated by Bougher et al. (1990) who predicted their existence using early models of the Martian thermosphere and coined the term “heat island”. In-situ temperature and composition data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission provided the first evidence for the existence of these features (Pilinski et al. 2018).

In this paper, we analyze the Martian heat islands using wind and composition data collected between August 2016 and December 2019. The data was predominately collected by the MAVEN Neutral Gas and Ion Mass Spectrometer (NGIMS) and temperatures were inferred from the altitude structure of measured compositions. The data is analyzed for both aphelion (Northern Summer) and perihelion (Southern Summer) conditions. We also compare the data with the Mars Global Ionosphere-Thermosphere (M-GITM) global circulation model (Bougher et al. 2015). The model allows for a detailed investigation of the major heating and cooling terms in the thermosphere.

We find evidence of dynamical heating features in the models and data near both the dusk and dawn terminators by analyzing the horizontal wind, temperature, and composition structures above 150 km altitude. These features correlate with the location of converging winds (both observed and modeled). The model indicates that the hottest thermospheric temperatures above 150 km occur in the location of the heat islands at both aphelion and perihelion. MAVEN data confirms that this is the case at aphelion. Analysis of the model heating terms confirms that the predominant heating results from wind convergence.

The Mars heat islands can provide useful diagnostic into the physics captured by global circulation models by examining their ability to reproduce the observed magnitude and location of dynamical heating. The heat islands are also relevant when estimating the aerodynamic drag forces on satellites in elliptical Mars orbits.

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