The Effect of Calibration of the Forward-Scattering Spectrometer Probe on the Sizing of Cloud Droplets

Abstract Cloud droplets were measured from an aircraft with an FSSP in summer cloud and in winter cloud. For 70 cloud penetrations, three cloud droplet volume spectra were derived using three different calibration schemes. The spectra were parameterized by the mean volume diameter, the effective diameter, the effective dispersion, the skewness and the kurtosis. These parameters were statistically intercompared using the Mann-Whitney test. The results show that, for the clouds studied, the mean volume diameter and the effective diameter are not significantly affected by the choice of the calibration scheme. However, the dispersion of the volume distribution, the skewness and the kurtosis are quite sensitive to the details of the calibration scheme and possibly to oscillations in the intensity of the scattered light signal, as described by Mie theory.