LONG-TERM VARIABILITY OF MODIS 3 KM AEROSOL OPTICAL DEPTH OVER INDIAN REGION

Abstract. The study examined the spatio-temporal variability, validation and climatological trend of MODIS Terra and Aqua level-2 Dark Target retrieval algorithms 3-km AOD over India region during 2001–2017. Analysis reveal the MODIS AOD shows significant variability in spatial extent; Indo-Gangetic plane having high aerosol loading and Southern peninsula shows relatively low aerosol loading in all seasons. The climatological zonal averaged (throughout India) AOD₅₀₀ are 0.401 ± 0.23 and 0.324 ± 0.64 for Terra and Aqua respectively whereas the ground measured all stations averaged AOD₅₀₀ is 0.43 ± 1.2 during study period. For validation we obtained daily AOD data from nine ground network stations across India. MODIS 3-km AOD shows good agreement with ground measurements. A total of 5646 and 4920 data points are utilized for validation of MODIS Terra and Aqua AODs respectively and the overall correlation coefficients and RMSE values are 0.94 & 0.08 and 0.72 & 0.17 for Terra and Aqua over the Indian region. However, during monsoon season, both the MODIS AODs are highly overestimated because of atmospheric noise and turbidity. Trend slopes and significances were calculated using Mann-Kendell test at nine selected stations and whole region. AOD shows a significant positive trend (99.9% confidence level) over India with an increasing rate of 2.35 yr⁻¹ and 2.03 yr⁻¹ for Terra and Aqua respectively. All stations annual AODs shows the increasing trend with different significance levels except Patiala. This study reveals the potential applications of the 3-km AOD product in aerosol climatology over Indian region.