Spectral and temporal characteristics of aerosol optical depth over a wet tropical location in North East India

A network of multi wavelength solar radiometer (MWR) stations has been in operation since the 1980s in India for measurement of aerosol optical depth (AOD). This network was augmented recently with the addition of a large number of stations located across the length and breath of India covering a variety of climate regimes. The spectral and temporal variations of aerosol optical depths observed over Dibrugarh located in the North East of India (27.3°N, 94.5°E) are investigated by analyzing the data obtained from a MWR during October 2001–September 2003 using the Langley technique. AOD varies with time of the day, month of the year and season. From January to April and October to December, aerosol optical depth decreases with wavelength whereas during May–September aerosol optical depth has been found to be nearly independent of wavelengths. AOD is higher during pre-monsoon season (March–May) and lower in the monsoon (June–September) season at about all wavelengths. The temporal variation of AOD over Dibrugarh have also been compared with those reported from selected locations in India.