Spatio-temporal trend and variability of MODIS and MISR Aerosol Optical Depth (AOD) and their relationship with prevailing meteorology and surface conditions during pre-monsoon period (2007-2016) over the Indian sub-continent

Abstract:

The pre-monsoon aerosol concentration plays a significant role in modifying precipitation amount over the Indian sub-continent. A large variety aerosol from different sources produces a complex radiative and climate response through the interaction with the hydrometeorological parameters. In this study, we analysed the space time dynamics of aerosol optical depth (AOD) in relation with the meteorological and surface parameters over Indian sub-continent during pre-monsoon season from 2007 to 2016. The Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging Spectroradiometer (MISR) derived level-3 aerosol products were used. The IMD gridded rainfall and temperature, ECMWF derived RH and wind velocity, and GLADS derived soil moisture data were also used. For space-time model, a pixel based linear model including anomaly detection and Mann-Kendall trend test were used, while, wavelet transformation was done for time series analysis of AOD. The results show a high concentration of AOD (~ 0.5) in the Indo-Gangetic basin (IGP) in MODIS and MISR data. The IGP and north-western India experienced high positive anomaly most of the years. The linear modelling shows increase of AOD with an increase of rainfall (β ~ 0.4), temperature (β ~ 0.03), RH (β ~0.02) and wind velocity (β ~ 0.2) most of the parts of India, however, decrease of AOD is observed with an increase of soil moisture (β < -0.04). Wavelet power spectrum in AOD time series trends and wavelet coherency test between AOD and all meteorology and surface parameters show significant power concentrated in higher band of 32-128 days throughout the study period. Although, diverse physiographic conditions, different climatic region, heterogenetic of spatial anthropogenic activities, etc are important in causing spatio-temporal variability of AOD. Meteorology and surface conditions are significant controlling factors in AOD concentration over this study period.