Micro pulse lidar observation of high altitude aerosol layers at Visakhapatnam located on the east coast of India

Abstract

Aerosol back scatter profiles obtained using a micro pulse lidar at Visakhapatnam, a station located on the east coast of peninsular India show certain high altitude aerosol layers during the months of March/ April 2005, 2006. Colocated aerosol optical depth measurements show an increase in AOD by 0.05 to 0.25 during the event when the layers were observed. The prevailing meteorology does not indicate any possible local entrainment of aerosol leading to the formation of elevated layers due to boundary layer dynamics. The 7 day back trajectory analysis shows that the possible origin of the layers could be from Arabia in 60% of the cases while it is from Indian sub-continent during the rest of the events. When the air mass flow is from the Indian sub-continent, there is a proportional increase in MODIS derived aerosol column fine mode fraction though it is not observed at the surface level. During the events when air mass flow is from Arabia, such an increase in column fine mode fraction was not observed but the angstrom size index which is a measure of the aerosol size distribution was low indicating that the elevated layers of Arabian origin could contain significant fraction of dust aerosol. Copyright 2007 by the American Geophysical Union.