Study on Probability Distributions of Multi-Timescale Aerosol OpticalDepth Using AERONET Data

The probability distribution analysis is performedfor multi-timescale aerosol optical depth (AOD)using AErosol RObotic NETwork (AERONET) level 2.0data. The maximum likelihood estimation is employed todetermine the best-fit probability density function (PDF),and the statement that the fitting Weibull distribution willbe light-tailed is proved true for these AOD samples. Thebest-fit PDF results for multi-site data show that the PDFof AOD samples with longer timescale in most sites tendsto be stably represented by lognormal distribution, whileWeibull distribution is a better fit for AOD samples withshort timescales. The reason for this difference is analyzedthrough tail characteristics of the two distributions,and an indicator for the selection between Weibull andlognormal distributions is suggested and validated. Theresult of this research is helpful for determining the mostaccurate AOD statistics for a given site and a given timescaleand for validating the retrieved AOD through itsPDF.