Abstract
Spatial and temporal variations in the Martian carbon monoxide (CO) cycle have been investigated through combining Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) retrievals of carbon monoxide mixing ratio and Mars Climate Sounder (MCS) temperature profiles with a Martian global circulation model (GCM) to produce the first global reanalysis of the Martian CO cycle.The reanalysis reduces the root mean square error between the forecast and CRISM CO retrievals by a factor of 2–4, dependent on the time of year. Forecasts initiated from the reanalysis show an improved match to standalone CRISM CO retrievals from northern winter solstice to northern summer solstice, indicating the benefit of data assimilation in simulating the CO abundance. The northern summer solstice CO minimum between 10∘S – 50∘S in the CRISM CO retrievals is found to be caused by a suppression of CO-enriched air leaking from the Hellas and Argyre basins, and is also strongly influenced by the amount of carbon dioxide condensing at the time. The GCM is the first reported to simulate the local CO minimum however it is weaker in strength, as CO-enriched air is also released northward in the area of Argyre basin in the GCM because of a shifted boundary between the southern polar vortex and mid-latitudes. The reanalysis, as a result of the assimilation of MCS temperature profiles, indicates that the polar vortex boundary is northward of Argyre basin and hence no northerly transport of CO-enriched air should be present over this location.Differences in local CO abundance between the reanalysis and GCM are also evident in spatio-temporal regions where no nearby CRISM CO retrievals are available as a result of alterations in local circulation and the sublimation/condensation of carbon dioxide through the combined assimilation of CRISM CO retrievals alongside MCS temperature profiles, illustrating how constraints can be imposed indirectly on the CO cycle through the powerful technique of data assimilation.
Highlights
Carbon monoxide plays an important role in the chemical stability of the martian atmosphere (McElroy and Donahue, 1972) and has been observed by a number of ground-based telescopes (Clancy et al, 1990; Lellouch et al, 1991; Krasnopolsky, 2007) and spacecraft in orbit around Mars (Billebaud et al, 2009; Encrenaz et al, 2006; Smith et al, 2009)
In this paper we investigate the effect of carbon monoxide (CO) assimilation using Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data and the inclusion of temperature profiles from the Mars Climate Sounder (MCS) instrument, both on the Mars Reconnaissance Orbiter (MRO) spacecraft, using a chemically active Mars global circulation model (GCM)
All simulations are started at LS =0◦ in Mars year (MY) 29 and finish at LS =332◦ in MY 29 to allow for a direct comparison between each different simulation
Summary
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Smithc aSchool of Physical Sciences, The Open University, Milton Keynes, MK7 6AA bSpace Science and Technology Department, Science and Technology Facilities Council, Rutherford.
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