THE ROLE OF HETEROGENEOUS FREEZING NUCLEATION IN UPPER TROPOSPHERIC CLOUDS - INFERENCES FROM SUCCESS

A temperature spectrum of heterogeneous freezing nuclei concentrations in continental air in the upper troposphere was determined based on a irborne measurements. Numerical model simulations incorporating ice fo rmation by heterogeneous and homogeneous freezing of deliquesced solub le aerosol particles were performed to investigate the effect of the h eterogeneous process on the microphysics of upper tropospheric clouds. Heterogeneous freezing nuclei were predicted to cause lower maximum c oncentrations of ice particles formed in clouds. These nuclei also ini tiate the first ice formation and act to broaden ice crystal size dist ributions in upper tropospheric clouds. Observations of ice formation in an orographic wave cloud supported these predictions.