Mercredi 7 mars (Guyancourt, amphithéâtre Gérard Mégie, 11h) Robert M. Haberle (NASA/Ames Research Center): "Orbital Climate Change on Mars: The Role of Clouds"

Variations in Mars’ orbit parameters have long been suspected of inducing changes in the planet’s climate system.  Published studies of this forcing mechanism have not included the role of clouds and how they alter the planet’s energy balance. In this seminar we will present results from the NASA/Ames Mars General Circulation Model that show the potential for a very strong cloud greenhouse effect at times in the past when summertime polar insolation was elevated with respect to present day. In some of our simulations the radiative effect of clouds increases global mean surface temperatures by over 30 Kelvins compared to the same simulation where the clouds are radiatively inert. The realism of this result depends on many factors, but among the most important is the model’s ability to accurately simulate the cloud formation process. We describe how this is done in the Ames model and discuss some preliminary simulations to assess its sensitivity to the dust cycle.