Accurate Retrieval of Asymmetry Parameter for Large and Complex Ice Crystals From In-Situ Polar Nephelometer Measurements

The retrieval of the asymmetry parameter from nephelometer measurements can be challenging due to the inability to detect the whole angular range. Here, we present a new method for retrieving the asymmetry parameter of ice crystals with relatively large size parameters (>50) from polar nephelometer measurements. We propose to fit the angular scattering measurement with a series of Legendre polynomials and the best fitted coefficients give the asymmetry parameter. The accuracy of the retrieval is analyzed by accessing the smoothness of the phase function, which is closely linked to the complexity of ice particle. It is found that the uncertainty of retrieval could be smaller than 0.01, provided the measured intensity profile is smooth enough. As an application, we report an case study on Arctic cirrus, which shows a mean value for the asymmetry parameter of 0.72.