Probabilistic model of shattering effect on in-cloud measurements

Abstract. A probabilistic model of the ice shattering effects on in-cloud measurements performed with instruments designed with inlets, which have the circular cross-section, is presented. Applications are made for the Polar Nephelometer and PMS FSSP instruments. The model provides rough estimates of the effects on microphysical measurements and assigns the key parameters that govern the efficiency of ice shattering. It is shown that experimental data are less affected by the shattering for clouds that have a lower proportion of large particles. The effects on derived integral microphysical parameters are shown to be very sensitive to the effective diameter of the ice fragments. The smaller the fragments from a given cloud particle are, the higher their effects are. Errors on Polar Nephelometer measurements were evaluated. It is shown that the ice particle shattering leads to the overestimation of the extinction coefficient. For example, for a given distribution with the effective diameter of 68 μm and with fragment effective diameters of 10 μm the extinction is overestimated by 25%. With larger particles having an effective diameter of 89 μm, the error increases up to 37%. As for the FSSP-300 instrument, under the same conditions the extinction coefficient is overrated by 17% and the number particle concentration is overestimated by 30%. The discussion of the results points out the main hypothesis which may seriously limit the reliability of the modelling results. Nevertheless, the magnitudes of the errors on extinction and particle concentration are of the same orders of those reported in the literature from experimental assessments.