Detailed modelling of cirrus clouds - an intercomparison of different approaches for homogeneous nucleation.
Abstract
We developed a cirrus model with detailed microphysics including homogeneous nucleation, deposition on ice crystal and riming of supercooled droplets on ice crystals. The model treats the particle distribution as two-dimensional, which allows to keep the information on the aerosol particles which act as CCN and determine the solute concentration of the droplet.To get accurately the number of crystals, homogeneous nucleation must be determined very carefully during the short period of cirrus formation. The formation period is limited by the consumption of water vapour by the strong depositional growth of the new small crystals. Therefore, these two processes should be treated closely. There are several approaches for the treatment of homogeneous nucleation. A comparison of those scheme have been published in Lin (JAS, 2002). A major problem in this intercomparison for homogeneous nucleation is that the models involved also use different description on ice particles. Thus this intercomparison does not allow a conclusion on which process " nucleation or deposition " is responsible for the different results. That's why we've implemented into our model three different schemes of nucleation for supercooled acid sulphuric solution droplets: the classical approach of Tabazadeh (GRL, 2000), the effective temperature model of DeMott (JGR, 1997), and the laboratory data set of Koop (Nature, 2000). With our detailed cirrus model for crystal growth we compared the three different parameterisation of nucleation, and tested the effect of solute concentration on the formation of cirrus clouds.We've also implemented a riming scheme based on the numerical solution of Bott (JAS, 2000) for two-dimensional particle distributions. We've seen that in pure cirrus conditions riming is negligible to explain ice particle size and also to explain the amount of residual aerosol mass.
- Publication:
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EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....5880M