The structure and variability of Mars dayside thermosphere from MAVEN NGIMS and IUVS measurements: Seasonal and solar activity trends in scale heights and temperatures

Abstract

Mars dayside thermospheric temperature and scale height trends were examined using measurements from the Neutral Gas Ion Mass Spectrometer (NGIMS) and the Imaging Ultraviolet Spectrograph (IUVS) on the Mars Atmosphere Volatile EvolutioN (MAVEN) spacecraft. Average scale heights (over 150–180 km for solar zenith angles ≤75°) from several different sampling periods were obtained from each instrument. NGIMS and IUVS scale height trends were found to be in good agreement, with both showing scale heights decreasing after perihelion and reaching a low value near aphelion (13.6 to 9.4 km). Between these two seasonal extremes, the temperature decreased by ∼70 K (from 240 to 170 K). These trends were also analyzed with respect to the changing solar flux reaching the planet, using the Lyman alpha irradiance measured by the Extreme Ultraviolet Monitor (EUVM) on MAVEN. Scale heights responded strongly to the changing solar flux. During this part of the MAVEN mission (October 2014 to May 2016), it was concluded that over longer timescales (at least several months), dayside thermospheric temperatures are chiefly driven by changing solar forcing, although it is the effects of changing heliocentric distance rather than changing solar activity which seem to have the greatest impact. Furthermore, effects of solar forcing were not observed on shorter timescales (less than a month), suggesting local wave effects may dominate solar forcing on these timescales. Finally, temperatures from two NGIMS sampling periods were compared to temperatures from the Mars Global Ionosphere‐Thermosphere Model (M‐GITM) and found to be in good agreement.

The Global-Scale Observations of the Limb and Disk (GOLD) Mission

“…This algorithm has been extensively documented (e.g., Strickland et al 2004aStrickland et al , 2004bMeier et al 2005;Crowley et al 2006;Paxton 2011, 2012). Exospheric temperatures (Texo) are derived by fitting a three-parameter Chapman type function (Lo et al 2015;Bougher et al 2017) to the LBH radiance profile above 200 km. The QEUV algorithm, which CPI originated, is based on the well-proven airglow modeling capabilities (AURIC and GLOW) that have been applied to previous missions, such as TIMED (Strickland et al , 2004a(Strickland et al , 2004b(Strickland et al , 2007.…”

Nightside ionosphere of Mars: Composition, vertical structure, and variability

“…Throughout this period the EUV irradiance at Mars changed by a factor of about 2, primarily owing to the varying Mars‐Sun distance rather than solar cycle variability. The EUV irradiance was highest during the beginning of the mission, when Mars was near perihelion [ Bougher et al , ; Lee et al , ].…”

The Impact of Crustal Magnetic Fields on the Thermal Structure of the Martian Upper Atmosphere

“…The role of solar forcing has been confirmed by a number of authors using the data from the drag experiments made on board Mars Global Surveyor (Forbes et al 2008;Krasnopolsky 2010), and the data acquired by the Neutral Gas and Ion Mass Spectrometer (NGIMS), the Accelerometer, as well as the Imaging Ultraviolet Spectrograph on board the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft (Jain et al 2015;Mahaffy et al 2015a;Bougher et al 2017;Zurek et al 2017).…”

“…Table 1 shows that SZA, L s , and F 10.7 are constrained within limited ranges for each campaign, implying that the observed temperature difference is unlikely caused by solar cycle, diurnal, and seasonal variations (e.g., Forbes et al 2008;Jain et al 2015;Bougher et al 2017;Zurek et al 2017). Meanwhile, the difference in relative O abundance is negligible in most cases based on the NGIMS measurements, which implies comparable CO 2 cooling between CF and NCF.…”