Aerosol plumes in a coastal environment revealed by lidar

A scanning backscatter lidar, operating at a wavelength of 1.06 μm, was used to measure the volume backscatter coefficient of coastal aerosol at the Mace Head Research Station on the west coast of Ireland during the PARFORCE experiments in September 1998 and June 1999. Lidar measurements under a fixed elevation angle at fixed time intervals provided the depth and evolution of the boundary layer throughout the day. Horizontal scans over the bay near the station indicate that waves breaking on the small islands and rocks in the bay near the station generate coherent plumes of a few hundred meters wide that propagate over distances of more than 5 km. Vertical scans have shown that the initial height of these plumes is a few tens of meters, rising to several hundreds of meters while advected over several kilometers. The backscatter coefficient in the plumes was between a factor of 2 and 10 higher than outside the plume. Large series of consecutive vertical cross sections showed that patches of aerosol plumes are taken aloft in the boundary layer to altitudes of more than one kilometer. So far, no relation was found between the horizontal and/or the vertical extent of the aerosol plumes and the air-to-sea temperature difference. The lidar measurements indicate that in situations that the wind is from over one of the islands the ambient aerosol concentrations can be enhanced by more than a factor 2 due to local aerosol sources