Sband radio occultation measurements of the atmosphere and topography of Mars with Mariner 9: Extended mission coverage of polar and intermediate latitudes

Abstract

A set of significant S band radio occultation measurements was obtained with Mariner 9 during May and June of 1972, for the first time yielding extensive occultation data on the north and south polar regions. The daytime temperature profiles, representative of a clear atmosphere, exhibit gradients (averaging −2.3°K/km) far smaller than those expected under conditions of radiative‐convective balance. The measured gradients are in good agreement with those computed for Stone's radiative dynamical models. The near‐surface temperatures (180°–190°K) measured in the Martian spring daytime on the north polar cap indicate that it may, at least in part, consist of water ice. Temperatures in the south polar area, measured in nighttime, were low enough for condensation of carbon dioxide to take place. Measurements of the height of the daytime ionosphere at solar zenith angles greater than 72° are lower than the expected heights of the ionization peak, possibly indicating about 25% cooling of the lower atmosphere between November and December of 1971 and May and June of 1972. Planetary radii obtained at latitudes ranging from +86° to −80° indicate a pronounced north‐south asymmetry. The south polar region is higher than the north polar area by an average of about 3.4 km; the entire southern hemisphere is 3–4 km higher than the northern hemisphere. A measurement was obtained near the summit of Middle Spot (Pavonis Lacus) showing it to rise about 13.5 km above the surounding terrain.

Recovery and validation of Mars ionospheric electron density profiles from Mariner 9

“…Based on these samples, we requested data tables and plots of ionospheric properties as functions of radial distance for all occultations for which ionospheric peak properties were reported in Kliore et al (1972b) and Kliore et al (1973). We assumed that the absence of reported peak properties for a given occultation meant that no useful ionospheric profile was delivered to the archive.…”

“…Tables in Kliore et al (1972b) and Kliore et al (1973) report latitude, longitude, solar zenith angle, peak electron density, peak radial distance, and peak altitude for each occultation. We verified that the peak electron densities and peak radial distances reported by Kliore et al (1972b) and Kliore et al (1973) are consistent with the recovered electron density profiles.…”

“…Generally speaking, pre-MGS work tended to use areographic latitudes and post-MGS work has tended to use areocentric latitudes. However, Kliore et al (1973) define latitude in terms of a spherical planet, which leads to areocentric latitudes. Since the difference between latitudes defined with these two conventions is in any case always less than 1°, we have interpreted the reported latitudes as modernera areocentric values (Smith et al 2001).…”

“…At the main ionospheric peak, they have found that the peak electron density is proportional to the square root of the cosine of solar zenith angle (Hantsch and Bauer 1990;Kliore 1992;Kliore et al 1973;Luhmann and Brace 1991;Schunk and Nagy 1980;Stewart and Hanson 1982;Zhang et al 1990). They have found, with the support of additional datasets, that the peak electron density increases with increasing solar irradiance (Hantsch and Bauer 1990;Shinagawa 1996;Stewart and Hanson 1982).…”

“…They have found, with the support of additional datasets, that the altitude of the peak electron density increases with increasing solar zenith angle (Hantsch and Bauer 1990;Luhmann and Brace 1991;Shinagawa 1996;Stewart and Hanson 1982;Zhang et al 1990). They have discovered that the ionospheric peak altitude is elevated significantly during dust storms (Hantsch and Bauer 1990;Kliore et al 1973;Luhmann and Brace 1991;Shinagawa 1996;Stewart and Hanson 1982;Wang and Nielsen 2003;Withers and Pratt 2013;Zhang et al 1990). …”