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Minimizing Instrumental Broadening of the Drop Size Distribution with the M-Fast-FSSP

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  • 1 Leibniz-Institute for Tropospheric Research, Leipzig, Germany
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Abstract

A modified version of the Fast-FSSP (the so-called M-Fast-FSSP) is introduced. It allows minimization of the instrumental broadening of measured cloud drop size distributions caused by laser beam inhomogeneities. This is achieved by applying a new technique based on a postexperiment stepwise reduction of the probe's sampling volume. For monodisperse glass bead samples it is shown that the width of the measured size distribution is considerably reduced when applying this technique, especially for large glass bead diameters. The instrumental broadening may exceed a factor of about 4 for a mean glass bead diameter of 30 μm. The M-Fast-FSSP was applied in two cloud measurement campaigns. For two specific cloud cases, the profile of the width of the measured drop size distribution changes significantly when applying the method.

Current affiliation: National Aeronautics and Space Administration Ames Research Center, Moffett Field, California

Corresponding author address: Sebastian Schmidt, Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany. Email: schmidt@tropos.de

Abstract

A modified version of the Fast-FSSP (the so-called M-Fast-FSSP) is introduced. It allows minimization of the instrumental broadening of measured cloud drop size distributions caused by laser beam inhomogeneities. This is achieved by applying a new technique based on a postexperiment stepwise reduction of the probe's sampling volume. For monodisperse glass bead samples it is shown that the width of the measured size distribution is considerably reduced when applying this technique, especially for large glass bead diameters. The instrumental broadening may exceed a factor of about 4 for a mean glass bead diameter of 30 μm. The M-Fast-FSSP was applied in two cloud measurement campaigns. For two specific cloud cases, the profile of the width of the measured drop size distribution changes significantly when applying the method.

Current affiliation: National Aeronautics and Space Administration Ames Research Center, Moffett Field, California

Corresponding author address: Sebastian Schmidt, Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany. Email: schmidt@tropos.de

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