The joint project 4DWOLKEN aims to improve our understanding of radiative transfer processes in realistic clouds in order to more accurately perform simulations of transport and exchange processes in dynamic atmospheric models. The joint project consists of the 4 parts "Coordination" (WP1000), "Measurements" (WP2000), "Radiative Transfer Modelling", (WP3000) and "Dynamic Atmospheric Modelling" (WP4000), all of them closely linked to each other. The main goal of the here described sub-project "Development of Exact 3D Radiative Transfer Models" is to further develop existing 3D radiative transfer models in order to 1) enable the simulation of radiative flux and radiance measurements performed in WP2000 and 2) to enable solar and thermal narrow- and broadband radiative transfer calculations that are suitable for the development of 2a) cloud radiative flux parameterizations and 2b) cloud remote sensing algorithms for realistically structured clouds fields. The results of these model developments will be used by other project partners: part 1) in WP 3200 "Validation and Improvement of Radiative Transfer Models", part 2a) in WP3300 "Development of Radiative Transfer Parameterizations" and WP4200 "3D Radiative Transfer Parameterization in Dynamical Models", and part 2b) in WP4200 "Validation of Radiative Effects". See the joint project plan and the work package project plans for details.
Within WP3100, the following existing radiative transfer models will be applied/improved: The forward Monte Carlo 3D solar radiative transfer models MC-IfMK and MC-IPA developed at the Institut für Meereskunde, Kiel (IfMK) and at the Institut für Physik der Atmosph&aunl;re, Heildelberg (IPA) and a backward 3D Monte Carlo microwave radiative transfer model 3RAD developed at IfMK and at the Meteorologisches Institut, Uni Bonn (MIUB). MC-IfMK and MC-IPA will be improved in order to better simulate radiance fields with high spectral resolution. To this end, the so-called Local Estimate method needs to be incorporated into both models. Results will be compared to 3D radiative transfer calculations from the Intercomparison of 3D Radiation Codes Project I3RC. The radiative transfer model input will be adapted to the spectral and directional properties of the radiation measurement devices in WP 2000 (radiometer, albedometer, spectrometer). This also implies the construction of spectrally high resolved atmospheric and cloud scattering and absorption properties. 3RAD will be extended to the thermal spectral range in order to simulate thermal radiance for 3D clouds. Furthermore, scattering and absorption at nonspherical raindrops will be incorporated into 3RAD in order to render possible a distinction between cloud droplets and precipitation from ground based measurements of polarized downward microwave emission from clouds.
Parallel to the model development, interfaces between the required radiative transfer input data and the available cloud data will be constructed. Cloud data will be provided from microwave radiometer and radar measurements obtained in WP2000, and from meso- to microscale atmospheric models (external partner: Andreas Chlond, MPI-Hamburg).
The model development is a joint action between the project partners MIUB, IPA and IfMK. Additional cooperation with the external partners Bernhard Mayer (DLR) and Stefan Bühler (Uni Bremen) will explore the applicability of more complex cloud and surface structures, and the extension of microwave radiative transfer models to the submillimeter spectral range.
Institute of Marine Research,
University of Kiel, IfM
Düsternbrooker Weg 20,
24105 Kiel, Germany