HR: 08:30h
AN: A41F-01    [Abstracts]
TI: Understanding Cloud Processes in Midlatitude Storms
AU: * Del Genio, A D
EM: adelgenio@giss.nasa.gov
AF: NASA/GISS, 2880 Broadway, New York, NY 10025 United States
AU: Bauer, M
EM: mbauer@giss.nasa.gov
AF: NASA/GISS, 2880 Broadway, New York, NY 10025 United States
AU: Naud, C
EM: cnaud@giss.nasa.gov
AF: NASA/GISS, 2880 Broadway, New York, NY 10025 United States
AU: Jonas, J
EM: jjonas@giss.nasa.gov
AF: NASA/GISS, 2880 Broadway, New York, NY 10025 United States
AU: Yao, M
EM: myao@giss.nasa.gov
AF: NASA/GISS, 2880 Broadway, New York, NY 10025 United States
AB: Clouds associated with extratropical baroclinic storms are often neglected in global climate models despite their importance for regional cloud feedback and climate changes in water availability. We discuss several issues associated with the simulation of these cloud systems in climate GCMs. In general, GCMs overestimate the occurrence of optically thick high clouds and underestimate midlevel cloud occurrence in such storms. For the GISS GCM we show that this bias is likely to be related to underestimates of the storm ageostrophic circulation and tilt of frontal surfaces, which also cause the model to underestimate the dynamical transport of water vapor and occurrence of midlatitude cirrus. GCMs make different assumptions about the conditions under which liquid vs. ice is created above the freezing level, usually making this a function of temperature alone. We use MODIS satellite data to argue that the temperature range of transition from liquid to ice varies systematically along the midlatitude storm tracks due to varying intensity and maturity of storms. There is also a hint in the satellite data of the transition from heterogeneous to homogeneous nucleation of ice at temperatures near 240 K. Both of these have implications for parameterizations of mixed phase processes in GCMs.
DE: 0320 Cloud physics and chemistry
DE: 3364 Synoptic-scale meteorology
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly