Kalisch, John (2011) Der Einfluss von Wolken auf den Strahlungsantrieb der Erde. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, Kiel, Germany, 147 pp.

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Abstract

The aim of this study is to estimate radiative budgets and radiative effects by clouds onto the radiation balance of the earth. The estimation was performed at the surface, the top of the atmosphere and for the atmospheric column. In addition, the surface radiative fluxes have been simulated by the single column model ECHAM5.
The robust data base of the radiative measurements was set up along five cruises of the icebreaker POLARSTERN and the corresponding satellite remote sensing by MSG. A full sky imager for a rough offshore application was developed to derive the total cloud amount and the cloud type. Utilizing a microwave radiometer, the atmospheric temperature and humidity profiles as well as the liquid water path were measured continuously. The surface net budget is dominated by the solar radiative component with a mean value of 144W/m2, whereas the solar impact is high for cirrus and low for stratus. At the top of the atmosphere the solar fluxes are predominantly within the daily net budgets at tropical latitudes.
This results in a radiative forcing of 37W/m2. The atmospheric column shows a strong thermal emittance and a slight solar absorption. Its net heat loss amounts to a total of −100W/m2. The strongest surface cloud longwave effectswere determined in the presence of low level clouds. Clouds with a high optical density induce strong negative solar effects when the solar altitude is high. The mean surface net effect is −34W/m2. For the purpose of calculating the mean surface net effect, a new parametrization was created, considering the total cloud amount and the solar zenith angle. At the top of the atmosphere the clear sky radiative fluxes are approached inaccurately. The average atmospheric cloud effect is −3W/m2. Cirrus clouds have little atmospheric solar effects and strong longwave effects, thus cirrus is the only cloud type causing a heating of the climate. The atmospheric longwave effects are highly negative for optical thick low level clouds. Mean atmospheric solar effects are positive for each cloud type. The atmospheric net effect is −4W/m2.
Based on ECHAM5 simulations, the surface solar effects are about 20W/m2 higher than the measured effects. Surface longwave effects are simulated well. Under existence of cirrus and stratus the model physics with its single cloud layer works exactly. The surface solar effects of convective clouds, especially stratocumulus, show a large overestimation of up to 120W/m2.

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