Thermospheric Structure and Variability of the Mars Terminator from
MAVEN/EUVM Solar Occultations
E. M. B. Thiemann, Laboratory for Atmospheric and Space Physics, U. of Colorado Boulder, USA
(thiemann@lasp.colorado.edu), F. Eparvier, S. Bougher, Department of Climate and Space Sciences and Engineering, U. of Michigan, Ann Arbor, USA., Collin Payne, Erdal Yiğit, Department of Physics, George Mason University, Fairfax, USA, F. Gasperini, Orion Space Solutions, Louisville, USA.

Abstract:
The Extreme Ultraviolet Monitor (EUVM)
onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter measures thermospheric density from about 110 to 200 km via solar occultations
using its 17-22 nm channel, in addition to EUVM’s
primary solar irradiance measurement. The EUVM
solar occultation data record ranges from late 2014
through 2021, spanning a large fraction of a solar
cycle and 3 Mars years. Features inherent to solar
occultations, namely their insensitivity to absolute
calibration and inherently fixed local time, allow for
the characterization of long-term variability of the
upper atmosphere. In this presentation, we show observed variations in thermospheric density and temperature with solar cycle and season. In particular,
we quantify the sensitivity of exospheric temperature
to solar EUV irradiance and show that the Dawn
terminator tends to be more sensitive to solar EUV
forcing than the Dusk terminator. We discuss possible causes of this feature and what insights it provides to the climatology of the Mars upper atmosphere. Additionally, we show how thermospheric
density varies with latitude at the terminator, and
how this structure changes with season and local
time. Underlying causes of prominent features, such
as higher density at high latitude dawn, are discussed.