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The Cirrus Parcel Model Comparison ProjectThe cirrus Parcel Model Comparison Project involves the systematic comparison of current models of ice crystal nucleation and growth for specified, typical, cirrus cloud environments. In Phase 1 of the project reported here, simulated cirrus cloud microphysical properties are compared for situations of "warm" (-40 C) and "cold" (-60 C) cirrus subject to updrafts of 4, 20 and 100 centimeters per second, respectively. Five models are participating in the project. These models employ explicit microphysical schemes wherein the size distribution of each class of particles (aerosols and ice crystals) is resolved into bins. Simulations are made including both homogeneous and heterogeneous ice nucleation mechanisms. A single initial aerosol population of sulfuric acid particles is prescribed for all simulations. To isolate the treatment of the homogeneous freezing (of haze drops) nucleation process, the heterogeneous nucleation mechanism is disabled for a second parallel set of simulations. Qualitative agreement is found amongst the models for the homogeneous-nucleation-only simulations, e.g., the number density of nucleated ice crystals increases with the strength of the prescribed updraft. However, non-negligible quantitative differences are found. Systematic bias exists between results of a model based on a modified classical theory approach and models using an effective freezing temperature approach to the treatment of nucleation. Each approach is constrained by critical freezing data from laboratory studies. This information is necessary, but not sufficient, to construct consistent formulae for the two approaches. Large haze particles may deviate considerably from equilibrium size in moderate to strong updrafts (20-100 centimeters per second) at -60 C when the commonly invoked equilibrium assumption is lifted. The resulting difference in particle-size-dependent solution concentration of haze particles may significantly affect the ice nucleation rate during the initial nucleation interval. The uptake rate for water vapor excess by ice crystals is another key component regulating the total number of nucleated ice crystals. This rate, the product of ice number concentration and ice crystal diffusional growth rate, partially controls the peak nucleation rate achieved in an air parcel and the duration of the active nucleation time period.
Document ID
20000074794
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Lin, Ruei-Fong
(Universities Space Research Association United States)
Starr, D.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
DeMott, P.
(CSU Unknown)
Cotten, R.
(Meteor. Res. Fl Unknown)
Jensen, E.
(NASA Ames Research Center Moffett Field, CA United States)
Sassen, K.
(Utah Univ. Salt Lake City, UT United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 2000
Subject Category
Meteorology And Climatology
Meeting Information
Meeting: 13th International Conference on Clouds and Precipitation
Location: Reno, NV
Country: United States
Start Date: August 14, 2000
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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