bbc workshop debilt, 18.–19. october 2004 reconstruction of three dimensional cloud fields from...
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BBC Workshop DeBilt, 18.–19. October 2004
Reconstruction of three dimensional cloud fields from two dimensional input datasets
Klemens Barfus & Franz H. Berger
Email: [email protected]
Technische Universität DresdenInstitute of Hydrology and MeteorologyDepartment of Meteorology01737 Tharandt, Germany
I H M
BBC Workshop
DeBilt, 18.–19. October 2004
Concept
Concept Data Modifications Reconstruction
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
BBC Workshop
DeBilt, 18.–19. October 2004 Data Modifications ReconstructionConcept
Example of input data
Combined data from September, 23, 2001area ~ 400 x 400 km
2 test areas
Problems
BBC Workshop
DeBilt, 18.–19. October 2004 Data Modifications ReconstructionConcept
• 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
BBC Workshop
DeBilt, 18.–19. October 2004 Data Modifications ReconstructionConcept
Liquid Water Path data from different sources
Comparison of spatial averages of LWP data for Cabauw
BBC Workshop
DeBilt, 18.–19. October 2004
• 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
Data Modifications ReconstructionConcept
Modifications of LM data
BBC Workshop
DeBilt, 18.–19. October 2004 Data Modifications ReconstructionConcept
Reconstruction of three dimensional cloud field
multiple linear regression from cloud top heightand LWP
cloud base height from nearest cloud base
(first steps of reconstruction:)
approximation of cloud base height from nearest cloud base in vertical slice
BBC Workshop
DeBilt, 18.–19. October 2004 Data Modifications ReconstructionConcept
• 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 ?
Reconstruction: open questions
BBC Workshop
DeBilt, 18.–19. October 2004 Data Modifications ReconstructionConcept
Cloudmasks
Which more realistic assumptions about cloud field structure can be applied ?
Assumptions of cloud field structure with very simple cloud masks
BBC Workshop
DeBilt, 18.–19. October 2004 Data Modifications ReconstructionConcept
Cloudfields
Reconstructed cloudfields
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 intoindividually simulated areas
BBC Workshop
DeBilt, 18.–19. October 2004 NextModifications Reconstruction Simulation
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