The variations of the Martian exobase altitude

Solar control of CO₂ ⁺ ultraviolet doublet emission on Mars

“…The SZA variation in peak emission altitude could be interpreted by the fact that the emission is peaked where the optical depth at relevant wavelengths reaches unity in the Martian upper atmosphere, also analogous to the interpretation of the established SZA variation in peak electron altitude according to the idealized Chapman theory (e.g., Fox and Weber, 2012). Finally, the solar cycle variation in peak altitude is driven by the expansion of the atmosphere with increasing solar activity, similar to the observed solar cycle variation in exobase altitude at Mars (Fu MH et al, 2020).…”

“…Finally, we emphasize that in obtaining the best‐fit linear relations, those measurements made with are excluded. This is because under such a condition, the MAVEN IUVS was coincidently observing the Martian upper atmosphere during global dust storms (Fu MH et al, 2020), which would elevate the entire brightness profile, including the emission peak, to higher altitudes (see also Section 4).…”

Species‐dependent Response of the Martian Ionosphere to the 2018 Global Dust Event

“…The response of the Martian upper atmosphere during the same GDS has also been reported by Chaufray et al (2020) using the MAVEN Imaging Ultraviolet Spectrograph (Gröller et al, 2015(Gröller et al, , 2018 observations, revealing an increase in CO 2 density by a factor of ∼ 2 at 110 km due to the heating of the lower atmosphere. Important consequences of the dust storms also include the rise of the mesospheric and thermospheric water content (e.g., Heavens et al, 2011;Stone et al, 2020;Vandaele et al, 2019;, the enhancement of hydrogen escape (e.g., Chaffin et al, 2014;Heavens et al, 2018), as well as the elevation of the exobase altitude (e.g., Fu et al, 2020).…”

Solar and Magnetic Control of Minor Ion Peaks in the Dayside Martian Ionosphere

“…A higher abundance of the parent neutrals likely makes a further contribution to the observed solar cycle variation, which is driven by enhanced photolysis of neutrals in the dayside Martian upper atmosphere. Meanwhile, the Martian atmosphere expands in response to increasing solar EUV and X‐ray irradiance as indicated by a rising exobase altitude (Fu et al, 2020). This naturally moves the ionosphere to higher altitudes and causes the elevation of all minor ion peak altitudes, a mechanism that also accounts for the known effect of planet‐encircling dust storms on the Martian ionospheric structure (e.g., Wang & Nielsen, 2003).…”