In this seminar, I present recent results on the structure, variability and energetics of the far upper atmosphere found by the method of solar occultation, where atmospheric properties are inferred using sunlight as it passes through an atmosphere. The extreme ultraviolet (EUV) band is strongly absorbed in the thermosphere, enabling EUV occultations to provide a unique window into a sparsely observed region of the atmosphere. I begin with new findings that clearly distinguish the roles of Mars’s large orbital eccentricity and the Sun’s 11-year solar cycle in driving the climatology of Mars’s thermosphere. I then turn my attention to Earth, where I show EUV occultations can be used to help improve a long-standing miscounting of the EUV energy input to the thermosphere as well as for quantifying energy dissipated by gravity waves in the thermosphere. Finally, I show results found using solar occultations at the 121.6 nm H Lyman-alpha transition to measure the variability of the inner geocorona, which has been inaccessible to past remote sensing techniques. Students have been a major contributor to these results and their participation is highlighted. This presentation also features future missions, including the upcoming Occultation Wave Limb Sounder (OWLS) mission, of which I am Principal Investigator (PI), planned for launch in early 2027 to measure the relation between gravity wave energy and thermospheric temperature, as well as a NASA-funded vacuum ultraviolet Fourier Transform Spectrometer technology development program, of which I’m also PI, intended for the Earth Coronal Hot Hydrogen Observatory (ECHHO) mission to measure the energetics of the geocorona.
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