Bernhard Lee Lindner

Ozone on Mars: The effects of clouds and airborne dust

Abstract Photochemistry in the winter polar atmosphere of Mars is examined for several latitudes, cloud types and dust abundances. Variations in cloud opacities and cloud types change O3 abundances only a few percent. However, typical dust abundances induce 10–50% increases in O3 abundances, primarily because photodissociation rates are drastically reduced by dust absorption. Furthermore, annual, latitudinal and seasonal cycles in dust opacity cause variations of 50% or greater in the corresponding cycles in O3 abundances. The reflectance spectroscopy technique that has been used to measure the O3 abundance may have difficulty detecting these variations.

Ozone heating in the Martian atmosphere

Abstract Ozone is shown to be a minor, although nonnegligible, heat source in the martian atmosphere, in contradiction to earlier reports which had suggested a larger contribution to the atmospheric heat budget by ozone. It is further shown that the observed hemispherical asymmetry in ozone abundance is unlikely to be a significant factor in the observed hemispherical asymmetry in the permanent polar caps. Ozone heating may still be an important consideration in the formation and decay of clouds and snowfall, although not as important as previously suggested.

The hemispherical asymmetry in the Martian polar caps

An energy balance model is used to study the behavior of CO2 ice on Mars. The effect of the solar zenith angle dependence of albedo is to lengthen CO2 ice lifetimes at the poles. Hemispherical asymmetries in cloud and dust abundance could result in the survival of seasonal CO2 ice through summer in the south and not in the north, in agreement with observations. CO2 ice observed in the summertime polar cap in the south could be of recent origin, although a permanent CO2 polar cap cannot be ruled out.

Sunlight penetration through the Martian polar caps: Effects on the thermal and frost budgets

An energy balance model of the seasonal polar caps on Mars is modified to include penetration of solar radiation into and through the ice. Penetration of solar radiation has no effect on subsurface temperature or total frost sublimation if seasonal ice overlies a dust surface. An effect is noted for seasonal ice which overlies the residual polar caps. For the case of an exposed water-ice residual polar cap, the temperature at depth is calculated to be up to several degrees warmer, and the calculated lifetime of seasonal CO2 frost is slightly lower when penetration of sunlight is properly treated in the model. For the case of a residual polar cap which is perennially covered by CO2 frost, the calculated lifetime of seasonal CO2 frost is very slightly increased as a result of sunlight penetration through the ice. Hence, penetration of sunlight into the ice helps to stabilize the observed dichotomy in the residual polar caps on Mars, although it is a small effect.

Remote sensing of clouds by multispectral sensors

A multispectral minimization approach that uses the wavelength dependence of the radiance rather than the magnitude of the radiance is advocated for the retrieval of cloud optical thickness, phase, and particle size by future sensors.

In situ Mars ozone detector

Abstract A balloon-borne UV photometer sensor package is proposed for measure atmospheric ozone on Mars. The instrument has been used on a balloon in the terrestrial stratosphere, and is possibly a Discovery Program sensor candidate. The objectives for this instrument are to observe O3 variability with cloud and dust amount, to measure the altitude dependence of O3, and to measure diurnal fluctuations in O3. There are no measurements to date of any of these variations. In-situ ozone measurements would significantly improve our understanding of Mars atmospheric chemistry and composition and the interaction of atmospheric chemistry with atmospheric radiation and dynamics. Measurements to date are highly uncertain, perhaps a factor of 3 or so uncertain23,26, due primarily to interference and masking by cloud and dust In-situ balloon measurements would avoid these problems, and would provide ‘ground truth’ which remote sensing techniques cannot Much interest has been generated over the past 5 years for a Mars Aeronomy Mission. This is a low cost alternative which in many respects will learn more information. This mission would also complement a proposed Japanese mission to study the chemistry of the Martian upper atmosphere41.

Cooling the Martian atmosphere: the spectral overlap of the CO2 15 μm band and dust

Abstract Careful consideration must be given to the simultaneous treatment of the radiative transfer of the CO2 15 μm band and dust. Calculations for the Martian winter polar region show that a simple sum of separately calculated CO2 cooling rates and dust cooling rates can easily result in a 30% error in the net cooling, particularly near the surface. CO2 and dust hinder each others ability to cool the atmosphere. Even during periods of low dust opacity, dust still reduces the efficacy of CO2 at cooling the atmosphere. At the other extreme when dust storms occur, CO2 still significantly impedes the ability of dust to cool the atmosphere. Hence, both CO2 and dust must be considered in radiative transfer models.