Water Vapor Saturation And Ice Cloud Occurrence In The
Atmosphere Of Mars
L. Poncin1,2, A. Kleinböhl1, D. M. Kass1, R. T. Clancy3, S. Aoki4, A. C. Vandaele5, 1jet Propulsion Laboratory, California Institute Of Technology, Pasadena, Ca, Usa (Armin.Kleinboehl@Jpl.Nasa.Gov), 2École
Supérieure Des Techniques Aéronautiques Et De Construction Automobile, Paris, France, 3space Science Institute, Boulder, Co, Usa, 4graduate School Of Frontier Sciences, The University Of Tokyo, Kashiwa, Japan
5
Royal Belgian Institute For Space Aeronomy, Brussels, Belgium.

Introduction:
The Vertical Distribution Of Water Vapor And Its
Relation To Ice Cloud Occurrence In The Martian Atmosphere Has Been A Longstanding Question. Saturation And Cloud Formation Are Major Factors That Constrain The Vertical Distribution Of Water Vapor. The
Altitude At Which Water Vapor Saturation Occurs Is
Largely Controlled By The Thermal Structure Of The Atmosphere And Varies With Season And In Response To
Dust Storm Occurrence. The Vertical Distribution Of
Water Vapor Has Recently Gained Additional Interest
With The Recognition That Middle Atmospheric Water
Vapor Can Photolyze, Leading To The Formation Of Hydrogen, Which In Turn Can Propagate To The Upper
Atmosphere And Escape. Hence The Transport Of Water
Vapor To The Middle Atmosphere Influences The Hydrogen Escape Rate And Quantifying Its Variation
Might Help Explain This Contribution To Hydrogen Escape And Consequently Water Loss From Mars.
The Saturation State Of Water Vapor In The Martian