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| Simulated nadir radiance over a field of cumulus clouds. | |
Solar and thermal radiation is the main driving force of atmospheric circulation and chemistry. In addition, radiation reflected or emitted by the Earth's surface and atmosphere is utilised by remote sensing techniques to derive information about properties of the atmosphere and the surface from observations in space. A profound knowledge of radiation and its interaction with the atmosphere is therefore essential for many fields in atmospheric science.
Radiation is influenced by a wide range of parameters. These include the position of the sun, the reflectivity of the Earth's surface, profiles of air pressure, humidity, and trace gases concentrations, the abundance, composition, and shape of particles (aerosols), as well as water and ice clouds. Water and ice clouds are key components for the following reasons:
- the influence of clouds (reflecting solar radiation and trapping thermal radiation) is comparatively large compared to that of the other parameters;
- about 70% of the Earth's surface are covered by clouds on average;
- the temperal and spatial variability of clouds (cloud cover, liquid and ice water content, droplet and particle size) is high.
For the calculation of irradiance, radiance, and actinic flux in the Earth\u2019s atmosphere we are developing different tools, including the three-dimensional MYSTIC model. The image shows as an example the radiance reflected by convective clouds over inhomogeneous surface, as it would be observed by a satellite instrument from space. In this example the sun shines from the south under a zenith angle of 30° which is obvious from the shadows. The cloud was generated by a cloud-resolving model. Such simulated radiance distributions can be used for development and test of new remote sensing methods. MYSTIC correctly includes all relevant scattering and absorption processes in an inhomogeneous atmosphere and is used as a reference model. MYSTIC is part of the freely available radiative transfer package libRadtran, also developed by our group.
Concerning radiation in the atmosphere, our main research interests is focued on the basic understanding of the interaction of clouds and radiation:
- Development and test of remote sensing algorithms and cloud detection schemes
- Improvement of the parameterization of clouds in regional and global weather and climate models
- Quantification of the impact of radiation on atmospheric chemistry
- Calculation and prediction of solar radiation and ultraviolet radiation at the surface