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

The probability distribution analysis is performed for multi-timescale aerosol optical depth (AOD) using AErosol RObotic NETwork (AERONET) level 2.0 data. The maximum likelihood estimation is employed to determine the best-fit probability density function (PDF), and the statement that the fitting Weibull distribution will be light-tailed is proved true for these AOD samples. The best-fit PDF results for multi-site data show that the PDF of AOD samples with longer timescale in most sites tends to be stably represented by lognormal distribution, while Weibull distribution is a better fit for AOD samples with short timescales. The reason for this difference is analyzed through tail characteristics of the two distributions, and an indicator for the selection between Weibull and lognormal distributions is suggested and validated. The result of this research is helpful for determining the most accurate AOD statistics for a given site and a given timescale and for validating the retrieved AOD through its PDF.