On the retrieval of circumsolar radiation from satellite observations and weather model output Bernhard Reinhardt.

Munchen, Ludwig-Maximilians-Universitat, Diss., 2013

A method was developed to determine and map circumsolar radiation (cs.rad.) to close the gap between increased demand for data on cs. rad. with regard to concentrating solar technologies and their limited availability. the effective radius and optical thickness of cirrus clouds were used as input, as well as mass loadings of several aerosol components. The core of the method is a parameterization that allows to compute the cs. rad. from tabulated coefficients. The evaluated aerosol mass loadings were obtained from the Integrated Forecast System (IFS) of the European Centre for Medium-Range Weather Forecasts. The cirrus cloud properties were retrieved from Meteosat Second Generation (MSG) measurements. Considering cirrus clouds the prevailing ice particle shape is an uncertainty factor as it cannot be determined from MSG but must be assumed a priori. An uncertainty of up to 50% in the mean cs. rad. was determined by using several ice particle shapes or shape mixtures in the retrieval process. the developed method was validated with ground measurements of the circumsolar ratio (CRS). In the case of cirrus clouds the frequency distributions obtained from MSG data match the ground observations well. However, for aerosol the CSR is considerably underestimated if the IFS output is used head on.