Sulfur Dioxide Variability in the Venus Atmosphere




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Recent observations of sulfur oxides (SO2, SO, OCS, and H2SO4) in Venus’ mesosphere have generated controversy and great interest in the scientific community. These observations revealed unexpected spatial patterns and spatial/temporal variability that have not been satisfactorily explained by models. Particularly intriguing are the layer of enhanced gas-phase SO2 and SO in the upper mesosphere, and variability in the maximum observed SO2 abundance and the equator-to-pole SO2 abundance gradient, seemingly on multi-year cycles, that is not uniquely linked to local time variations. Sulfur oxide chemistry on Venus is closely linked to the global-scale cloud and haze layers, which are composed primarily of concentrated sulfuric acid. Consequently, sulfur oxide observations provide important insight into the ongoing chemical evolution of Venus’ atmosphere, atmospheric dynamics, and possible volcanism.

Existing observations have been obtained using multiple platforms, observing techniques, and wavelengths. Each has its own unique strengths and limitations. Although there is strong agreement on some features, there are significant unresolved apparent disagreements among current observations and between observations and models. These apparent disagreements need to be analyzed and assessed carefully to synthesize a clear understanding of sulfur oxide chemistry on Venus. This requires bringing together observers and modelers from research groups in Europe, Russia, the United States, and Australia. The team of experts that we propose will investigate different aspects linked to the presence of SO2 on Venus. These investigations will be performed via
  1. the comparison and validation of observations, from past missions, Venus Express, Earth-based telescopes, and the Earth-orbiting Hubble Space Telescope;
  2. modeling of the SO2 and sulfur-oxide family photochemistry; and
  3. modeling of other processes involving SO2 and the sulfur-oxide family such as cloud formation.
The proposed International Team activity is timed to take advantage of a planned scientific observing campaign focusing on measurements of SO2 and related sulfur cycle compounds, which is scheduled to take place in September-October 2013. Several of the key sulfur-oxide family species will be directly observed including: SO2, SO, OCS, H2SO4 and aerosols. The coordinated observation campaign provides an unprecedented opportunity for comparisons among the observational and theoretical modeling techniques involved in defining the past and current variability of SO2 and related gases.

Two separate proposals entitled "Towards a Self Consistent Thermal Structure Model of the Venus Atmosphere from Venus Express Observations [+LINK]" and "Improved models of Venus clouds [+LINK]" are also being submitted to ISSI at the same time by Dr. S. Limaye and Dr. C. Wilson respectively. All three proposals are complementary in many aspects. We propose to coordinate our meetings to provide overlap for some of the respective participants (and team leaders) to enable cross-fertilization.