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Discrimination between thin cirrus and and tropospheric aerosol using multiple measurements from Darwin ARCS

Mitchell, Ross CSIRO

Category: Aerosols

Thin cirrus cloud occurs frequently in the tropics, and is often difficult to distinguish from tropospheric aerosol on the basis of temporal variations in ground based measurements, since both can be rather spatially uniform. In this study we investigate their discrimination by combining data from three instruments at the Darwin Atmospheric Radiation and Cloud Station (ARCS): the Cimel sun photometer (CSP), the micropulse lidar (MPL), and the total sky imager (TSI). The study was carried out over the dry season of 2005, with the usual widespread burning of tropical savanna leading to extensive smoke plumes. It is shown that the locus of data in plots of Angstrom exponent versus aerosol optical depth derived from the CSP provides clear discrimination between cirrus and smoke plumes, with the MPL and TSI used to identify the makeup of the atmosphere. In addition, the same method allows identification of cases where aged background aerosol is the dominant particulate species. The study provides a training set for algorithm development aimed at discrimination between thin cirrus and tropospheric aerosol on the basis of multi-spectral sun photometry alone.

This poster will be displayed at the ARM Science Team Meeting.