An Investigation of the Elevated Aerosol Layer Using a Polarization Lidar Over a Tropical Rural Site in India

Polarization lidar observations were made to study the transport of an elevated aerosol layer over Gadanki, India (13.45° N, 79.17° E) during the pre-monsoon period of the year 2009. Observations show significant aerosol layering within and above the boundary layer. Coordinated observations with radiosondes were carried out from 2 to 10 April 2009. Temporal and spatial variations of the parameters are studied for the boundary layer (≈ 2.5 km) and up to 5 km. The backscattering coefficient and the depolarization ratio are observed to increase and decrease with an increase in humidity, respectively. Clouds are not formed, indicating less efficiency of the aerosol in acting as condensation nuclei. The transport of the elevated aerosol layer is investigated using a back-trajectory analysis, revealing that the transported layer originating from the central Indian region has a depolarization ratio of at least 0.05. From model analysis and satellite fire-count data, it is inferred that the source of the aerosol layer is wildfire events over the central Indian region. The elevated smoke-aerosol layer (not mixing with the boundary layer) has implications for the altering of the temperature profile of the atmosphere and the suppression of cloud formation.