HR: 1340h
AN: P23A-1086    [Abstracts]
TI: Laboratory Measurements for Ice Cloud Nucleation Under Martian Atmospheric Conditions on Various Dust Analogs
AU: * Phebus, B D
EM: phebuscouple@hotmail.com
AF: NASA Ames Research Center, N-245, Moffett Field, CA 94035, United States
AU: * Phebus, B D
EM: phebuscouple@hotmail.com
AF: San Jose State University, One Washington Square, San Jose, CA 95192, United States
AU: Iraci, L T
EM: Laura.T.Iraci@nasa.gov
AF: NASA Ames Research Center, N-245, Moffett Field, CA 94035, United States
AU: Colaprete, A
EM: Anthony.Colaprete-1@nasa.gov
AF: NASA Ames Research Center, N-245, Moffett Field, CA 94035, United States
AB: Understanding the role of water ice clouds in the Martian water cycle and climate as observed by Mars Global Surveyor, Mars Reconnaissance Orbiter, and Mars Odyssey depends on cloud properties such as particle size and number distributions. These, in turn, depend on poorly understood heterogeneous nucleation properties. Using classical nucleation theory, we have investigated the effect of substrate mineralogy and other parameters on model variables such as the contact parameter, m, and critical saturation ratio, S, defined as the partial pressure at nucleation divided by the equilibrium vapor pressure at the same temperature. Laboratory experiments have been performed under Martian temperature and water partial pressure conditions to determine S as a function of temperature and dust composition. Using infrared spectroscopy to monitor ice nucleation and growth, we find values of S ranging from 1 to 7 for water pressures between 5x10^-7 and 1x10^-4 torr and temperatures between 155 and 185 K. Below 175 K, significant supersaturation conditions may be required to nucleate water ice clouds on dust particles. The physical basis for this temperature dependence will be discussed, and simulations using the NASA Ames Mars General Circulation Model will examine the implications of these findings for the cycling of water between the surface and atmosphere.
DE: 3311 Clouds and aerosols
DE: 3337 Global climate models (1626, 4928)
DE: 5405 Atmospheres (0343, 1060)
DE: 5422 Ices
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting