MGS Radio Science electron density profiles: Interannual variability and implications for the Martian neutral atmosphere

Abstract

[1] Martian electron density profiles provided by the Mars Global Surveyor (MGS) Radio Science (RS) experiment over the 95-200 km altitude range indicate wthat the height of the electron peak and the longitudinal structure of the peak height are sensitive indicators of the physical state of the Mars lower and upper atmospheres. The present analysis is carried out on five sets of occultation profiles, all at high solar zenith angles (SZA). Variations spanning 2 Martian years are investigated near aphelion conditions at high northern latitudes (64.7-77.6N) making use of four of these data sets. A mean ionospheric peak height of 133.5-135 km is obtained near SZA = 78-82°; a corresponding mean peak density of 7.3-8.5 Â 10 4 cm À3 is also measured during solar moderate conditions at Mars. Strong wave number 2-3 oscillations in peak heights are consistently observed as a function of longitude over the 2 Martian years. These observed ionospheric features are remarkably similar during aphelion conditions 1 Martian year apart. This year-to-year repeatability in the thermosphere-ionosphere structure is consistent with that observed in multiyear aphelion temperature data of the Mars lower atmosphere [Clancy et al., 2000; Smith, 2004]. Coupled Mars general circulation model (MGCM) and Mars thermospheric general circulation model (MTGCM) codes are run for Mars aphelion conditions, yielding mean and longitude variable ionospheric peak heights that reasonably match RS observations. A tidal decomposition of MTGCM thermospheric densities shows that observed ionospheric wave number 3 features are linked to a nonmigrating tidal mode with semidiurnal period (s = 2) and zonal wave number 1 (s = À1) characteristics. The height of this photochemically determined ionospheric peak should be monitored regularly.

The Aeronomy of Mars: Characterization by MAVEN of the Upper Atmosphere Reservoir That Regulates Volatile Escape

“…The neutral thermospheric waves are also observed to have a corresponding impact on the ionosphere structure; e.g., the height of the main ionospheric peak varies in step with these longitude features (e.g. Bougher et al 2004Withers 2009;Haider et al 2011). Dust storm impacts on the upper atmosphere are only beginning to be observed and understood (see reviews by England and Lillis 2012;Withers and Pratt 2013).…”

“…And, of course the ionosphere responds to changes in the neutral atmosphere structure (e.g. Bougher et al 2004. The Mars TIE system constitutes the atmospheric reservoir (i.e.…”

Neutral Upper Atmosphere and Ionosphere Modeling

“…The Mars TGCM (MTGCM) is a finite difference primitive equation model that selfconsistently solves for time-dependent neutral temperatures, neutral-ion densities, and three component neutral winds over the Mars globe (e.g., Bougher et al 1999aBougher et al , 1999bBougher et al , 2000Bougher et al , 2002Bougher et al , 2004Bougher et al , 2006bBell et al 2007). The MTGCM code is adapted from the NCAR TGCM framework (see Sect.…”

Solar System Ionospheres

“…Follow-up studies of day-to-day solar forcing of both the M1 and M2 ionospheric layers at Mars and the E and F1 layers at Earth were described in Rishbeth and Mendillo (2004). Month-to-month periods of variability using MGS data were then examined for peak density by , and in the topside ionosphere by Breus et al (2004). Studies over solar cycle time periods were conducted prior to MGS at Mars (Bauer and Hantsch 1989;Hantsch and Bauer 1990), and at Venus and Mars by Kliore and Mullen (1989) and Kliore (1992).…”