Carbon monoxide told about the circulation in the atmosphere of Mars

(ORDO NEWS) — The orbiter of the European-Russian program “ExoMars” was able to build a map of the global circulation in the atmosphere of Mars. This was done by tracking the movement of carbon monoxide molecules. At the same time, scientists were able to identify changes in the atmosphere caused by global dust storms. The article was published in the journal Nature Geosciences, briefly about the work is described on the IKI RAS website.

Carbon monoxide (CO) plays an important role in the Martian atmosphere, participating in the chemical cycles of both hydrogen and oxygen. It is formed in the upper atmosphere (at altitudes of about 60 kilometers) during the photolysis of CO2, after which, moving with atmospheric masses to lower altitudes, the CO molecules are most likely to be captured by the hydroxyl radical OH and cease to exist, again turning into CO2 and water. Since the lifetime of one CO molecule is estimated at about 2.5 Earth years, then from changes in the concentration of carbon monoxide in the atmosphere of Mars, one can determine how the atmospheric masses move depending on the season and estimate how much water vapor is in the atmosphere and what is its oxidizing capacity.

A group of Russian, French and American planetary scientists led by Kevin S. Olsen from the University of Oxford has published the results of the analysis of data collected by the Russian Atmospheric Chemistry Suite (ACS), installed on board the TGO (Trace Gar Orbiter) probe, which has been studying the atmosphere of Mars since 2016. Scientists worked with data from the MIR spectrometer collected in April-June 2018, which also covered a global dust storm. This device monitors how various substances in the atmosphere absorb some of the solar radiation, which is reflected in the observed spectra.

The concentration of carbon monoxide in the atmosphere of Mars turned out to be heterogeneous. At altitudes up to 80 kilometers, the volume fraction of CO near the equator is about one thousand parts per million, and when moving south, it rises to 1260 parts per million. At altitudes above 80 kilometers, where CO2 photolysis occurs, the carbon monoxide content rises sharply to five thousand parts per million. However, the models predicted that the surge should start at an altitude of 60 kilometers, which indicates an underestimation of the rate of carbon monoxide transport upward. At high latitudes, the concentration of carbon monoxide began to rise as early as 40 kilometers, reaching values ​​of 2000-3000 parts per million, which is more than predicted by the models.

Thus, at the equator of Mars, ascending currents predominate, heating the atmosphere, and near the poles – downdrafts. The circulation of the atmosphere in the form of two Headley cells is fast enough and for one or two weeks, it mixes the atmosphere, while in the polar regions this process is slower.

As for the global dust storm that raged after the northern autumnal equinox, during the observation period the average concentration of carbon monoxide fell by about 20 percent, but the transport of CO from the lower atmosphere to the upper layers increased. In this case, the lower atmosphere heats up and expands more, the concentration of water vapor increases and clouds gather less often. Observations carried out after the dust storm showed that the concentration of carbon monoxide in the atmosphere remains approximately the same up to heights of about 100 kilometers.

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