Relationship between BGA and clouds

The frequency distribution for the probability of occurrence for BR higher than 6 is shown in Fig. 7. From these three-year cases, we found that most cases (BR > 6) occurred when RH was higher than 60%-70%. This can be one of the causative reasons that would lead to the growth of the aerosol particles by condensation, thus changing their optical properties. This result is similar to that of Hanel3 and Fitzerald et al.11

The correlation of maximum extinction coefficient and maximum DR of cloud cases is shown in Fig. 8. Most of the cloud layers (RH > 70%) have the maximum DR lower than 0.1. The cases, which have the maximum extinction coefficient higher than 1 (1/km), showed a sharp increasing trend with increasing DR. This may be possibly due to the multi-scattering effect or also can be due to the presence of large particles with nonspherical shapes that can produce large scattering which can be related to long-range transport of Asian dust storms with moisture and pollutants.12

Fig. 8. The relationship between maximum depolarization ratio and maximum extinction coefficient of cloud events with respect to RH in Spring from 2002 to 2004.

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