BBC Workshop DeBilt, 18.–19. October 2004

1. Technische Universität Dresden Institute of Hydrology and Meteorology Department of Meteorology 01737 Tharandt, Germany Reconstruction of three dimensional cloud fields from two dimensional input datasets Klemens Barfus & Franz H. Berger Email:klemens.barfus@forst.tu-dresden.de BBC Workshop DeBilt, 18.–19. October 2004

2. BBC Workshop DeBilt, 18.–19. October 2004 Concept Data Modifications Reconstruction Concept 1. dataset: cloud parameters from satellite (liquid water path, cloud top height, cloud coverage) 2. dataset: time series of microwave radiometer and cloud radar from inside of satellite observed volume (profiles of liquid water content, cloud base height) • Reconstruction of three dimensional cloud fields from two input data sets of cloud parameters • Validate the reconstructed cloud field with radiative transfer modelling

3. BBC Workshop DeBilt, 18.–19. October 2004 Concept Data Modifications Reconstruction Example of input data Combined data from September, 23, 2001 area ~ 400 x 400 km 2 test areas

4. BBC Workshop DeBilt, 18.–19. October 2004 Concept Data Modifications Reconstruction Problems • measured three dimensional cloud fields does not exist ⇨ for the development of method modeled data are needed • data of Lokalmodell of the German Weather Service with a spatial resolution of 1 km and storage of subgrid cloud water are used ⇨ problem: liquid water is to low – modified with liquid water from satellite ⇨ problem: subgrid cloud structure is not known

5. Concept Data Modifications Reconstruction Liquid Water Path data from different sources Comparison of spatial averages of LWP data for Cabauw BBC Workshop DeBilt, 18.–19. October 2004

6. BBC Workshop DeBilt, 18.–19. October 2004 Concept Data Modifications Reconstruction Modifications of LM data • Scaling up liquid water path from satellite with liquid water path from microwave radiometer • Scaling up liquid water path from LM with scaled liquid water path from satellite (with conservation of lwc/lwp ratios of the different levels) • Erase liquid water path in columns, where satellite indicates cloud free conditions • Replace columns indicated as cloudy by satellite but in LM cloudfree with best fitting column from the neighbourhood

7. multiple linear regression from cloud top height and LWP cloud base height from nearest cloud base BBC Workshop DeBilt, 18.–19. October 2004 Concept Data Modifications Reconstruction Reconstruction of three dimensional cloud field • (first steps of reconstruction:) • approximation of cloud base height from nearest cloud base in vertical slice

8. BBC Workshop DeBilt, 18.–19. October 2004 Concept Data Modifications Reconstruction Reconstruction: open questions • distribution of cloud water according to lwc profile of best fitting cloud concerning cloud thickness from the vertical slice other lwc profiles ? • problem: subgrid cloud structure has to be defined which cloud mask ? • problem: parametrisation of effective radius ⇨ parametrisation from Bower et al. (1994) other parametrisations of effective radius ?

9. BBC Workshop DeBilt, 18.–19. October 2004 Concept Data Modifications Reconstruction Cloudmasks Assumptions of cloud field structure with very simple cloud masks Which more realistic assumptions about cloud field structure can be applied ?

10. BBC Workshop DeBilt, 18.–19. October 2004 Concept Data Modifications Reconstruction Cloudfields Reconstructed cloudfields

11. BBC Workshop DeBilt, 18.–19. October 2004 Data Modifications Reconstruction Simulation Radiative transfer modelling SHDOM cannot simulate the whole area at once - area has to be subdivided into individually simulated areas

12. BBC Workshop DeBilt, 18.–19. October 2004 next • other parametrisations of cloud field • differences in radiation field from different cloud field realizations • use mc-unik (Monte Carlo Code from Uni Kiel) • use surrogate cloud fields from Victor Modifications Reconstruction Simulation Next