Clouds are the main energy modulators and regulate exchange processes between the Earth's surface and the atmosphere. These exchange processes are characterized by a strong coupling between dynamics, thermodynamics and atmospheric radiative transfer. There are many findings which indicate that the widely employed classical 1D radiative transfer models are completely inappropriate to treat realistic, horizontally and vertically inhomogeneous cloudiness.
In this project methods will be employed which are based on 3D extensions of the so-called discrete ordinate method for radiative transfer as well as on Monte Carlo methods to tackle radiative transfer problems in realistic media. These methods will be employed to determine radiative flux densities and radiative heating/cooling rates.
The exact radiative transfer models require information on cloud morphology and on the microphysics of aerosol particles and cloud drops. Two avenues will be explored to supply this information: i) Cloud-resolving models, such as GESIMA, LM and LES, will be employed to generate 3D cloud liquid water fields , and , ii) dedicated observations by radar and microwave techniques, in-situ measurements of both spectral radiative flux densities as well as aerosol and cloud microphysical variables, spectroscopic nadir radiance observations and satellite derived observations will be used to generate consistent input information for the radiation models. The observations will be used to validate the 3D radiative transfer models on a thorough basis.
The following scientific issues will be investigated: 1) Simulation of reflection, transmission and absorption for selected wavelength intervals in boundary layer and cumulus clouds. Comparison of simulations with radiation measurements. 2) Investigation of the variability of cloud water/ice and its consequence for the radiative budget of the cloud. Which parameters can be used to express this variability? 3) Identification of spectral regions which show enhanced cloud absorption. Does this enhancement depend on the type of cloud and its inhomogeneity? 4) What can be learned from the radiation balance and from 3D radiative effects in the longwave region? 5) Development of parameterizations to improve radiative transfer in cloud-resolving (LM, GESIMA) and non-cloud-resolving (HRM, hydrostatic regional model) mesoscale models.
University of Leipzig
Leipzig, 04103 Germany