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Abstract
During the last decades millimeter-wave radars have been established as useful systems to detect hydrometeors and to derive macro- and microphysical cloud parameters. In addition to the backscattered signals from cloud and precipitation droplets, there are also returns from non-hydrometeors like dust or insects. Especially the boundary layer is contaminated by these targets (plankton) which have to be removed before applying cloud-retrieval algorithms. The upper boundary of the insect contaminated range follows obviously quite well in its diurnal cycle the top of the mixed-layer height, leading to the idea to develop an algorithm for determination of the plankton layer and to compare it with mixed-layer height retrievals of other (well established) methods.
Since November 2003 the Richard-Aßmann Observatory Lindenberg of the German Meteorological Service (DWD) has been continuously operating a 35.5 GHz coherent and polarimetric cloud radar to measure vertical profiles of the reflectivity, Doppler velocity, spectral width and linear polarisation ratio (LDR) between 250 m and 15 km height. As part of the standard data processing the LDR is used to separate between hydrometeors and non-hydrometeors (particularly insects).
This contribution will present a method, deriving the top of the mixed-layer height on base of the plankton reflectivity gradients. An application to several days in summer 2007 shows promising results compared to radiosondes-derived mixed-layer heights as well as to model data.