IMPACT OF PRIMARY ICE NUCLEATION PARAMETERIZATIONS ON THE FORMATION AND MAINTENANCE OF CIRRUS

Different ice nucleation algorithms are implemented in a cloud microph ysical scheme and numerical simulations of clouds are performed using a three-dimensional mesoscale model. The predicted ice crystal fields are found to be sensitive to the different modes of calculation of the number of deposition/condensation freezing nuclei and contact freezin g nuclei. Also a time and supercooling dependence of this sensitivity is established. The general features of the cirrus clouds observed by the research aircraft Falcon during the 1989 ICE (International Cirrus Experiment) mission ICE212 are compared to those of the cirrus clouds generated by the model. The cloud top height, the cloud ice content a nd the ice number concentrations seem to be reproduced well.