HR: 10:20h
AN: A11H-01    [PDF]
TI: The role of cubic ice in dehydration of cold clouds
AU: * Murphy, D M
EM: dmurphy@al.noaa.gov
AF: Aeronomy Laboratory, NOAA, 325 Broadway, Boulder, CO 80305 United States
AB: Cubic ice is a metastable form of ice with very similar physical properties but different crystal symmetry than normal, hexagonal ice. Below 200 K, water preferentially nucleates to Ic, then transforms to the more stable Ih in minutes to days. As a metastable phase, cubic ice will necessarily have a higher vapor pressure than hexagonal ice. A cloud parcel model shows that nucleation to cubic ice, conversion to hexagonal ice, and the vapor pressure differential together produce larger ice crystals that can more effectively dehydrate air. The modeled effect is largest at 180 to 200 K, just the range most important for the tropical tropopause and polar stratospheric clouds. The cloud model also produces a wider size distribution when cubic ice is included, in agreement with observations. Past observations of cubic ice in the atmosphere are consistent with the modeled behavior.
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting