Improved algorithms to generate 3-dimensional cloud fields for use in radiative transfer modelling
Zusammenfassung der Projektergebnisse
For solving multidimensional radiative transfer problems in the cloudy atmosphere, one needs not only a good Radiative Transfer (RT) model, but also realistic 2D or 3D cloud fields. The most used 3D cloud fields for research into cloud structure are fields from cloud models or fractal cloud fields. We have developed algorithms to generate surrogate fields where the power spectrum and the shape of the distribution can be chosen freely and independently. This facilitates sensitivity studies and allows generating fields that have a close fit with measurements. The latter is important as clouds have such a complicated structure that it cannot be measured fully. Therefore, methods to generate surrogate fields based on measurements are needed for empirical studies, such as closure studies or studies that need to bring measurements, made at different scales, together. In this project we have developed constrained stochastic simulation algorithms that including spatial information, e.g. the liquid water path of a scan of a ground-based scanning microwave radiometer. This makes the standard Iterative Amplitude Adjusted Fourier Transform (IAAFT) algorithm an interpolation method that preserves structure and allows for closure studies with radiation point-measurements. Furthermore we have worked on a version of the IAAFT algorithm where the Fourier transform is replaced by a continuous wavelet transform. This allows the additional stochastic modelling of the intermittence, in the sense of the variance of the variance, of the cloud fields. In the field of climate research, the IAAFT algorithm has been used for downscaling of precipitation and to generate a benchmark dataset for homogenisation algorithms.
Projektbezogene Publikationen (Auswahl)
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Combining surrogate clouds with geostatistics to ease the comparisons of point radiation measurements with cloud measurements. ISTP2009, 18-23 October, 2009, Delft University of Technology, The Netherlands
Venema, V., R. Lindau, T. Varnai, and C. Simmer
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Multi-stationäre Simulationen von täglichen Niederschlagssummen mit einem neuen auf Surrogate basierenden Wettergenerator und Selbstorganisierenden Merkmalskarten. 8. Deutsche Klimatagung, Universitätsclub Bonn, Deutschland, 5. bis 8. Oktober 2009
Sauter, T. and V. Venema
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A new algorithm for the downscaling of cloud fields. Quart. J. Royal. Meteorol. Soc., 2010
Venema, V., S. Gimeno García, and C. Simmer
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irst results from the COST-HOME monthly benchmark dataset with temperature and precipitation data for testing homogenisation algorithms. European Geosciences Union, General Assembly 2010, Vienna, Austria, 02- 07 May 2010
Venema, V. O.Mestre, E. Aguilar, I. Auer, J.A. Guijarro, P. Domonkos, P. Stepanek, P. Zahradnicek, J. Viarre, G. Müller-Westermeier, T. Szentimrey, M. Lakatos, C.N. Williams, M. Menne, D. Rasol, E. Rustemeier, G. Vertacnik, K. Kolokythas, T. Marinova, L. Andresen, F. Acquaotta, S. Fratianni, T. Likso, S. Cheval, M. Klancar, M. Brunetti, Ch. Gruber, M.P. Duran, and Th. Brandsma
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Precipitation downscaling under climate change. Recent developments to bridge the gap between dynamical models and the end user. Reviews in Geophysics, 2010
Maraun, D., F. Wetterhall, A. M. Ireson, R. E. Chandler, E. J. Kendon, M. Widmann, S. Brienen, H. W. Rust, T. Sauter, M. Themeßl, V. K. C. Venema, K. P. Chun, C. M. Goodess, R. G. Jones, C. Onof, M. Vrac, and I. Thiele-Eich
