Jahnke, Inger (2008) "Broken Cloud Effect" aus Beobachtung und Modell. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 77 pp.

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Abstract

This diploma thesis takes a look at the “Broken Cloud Effect” in different regions in the world and in a radiative transfer model. The “Broken Cloud Effect” describes the fact that there can get more shortwave radiation to the ground under broken cloud conditions than under clear sky conditions. At Sylt have been found absolute enhancements of the solar radiation with respect to clear sky conditions of 537W/m2. This is a record in measured enhancements in radiation at sylt. Out of the enhancements of solar radiation in percentage of the incoming radiation at clear sky conditions came the result that over water there were enhancements up to 50%, over green vegetation up to 70% and over snow up to 90%. So the surface albedo plays agreat role in enhancements of the solar radiation. Furthermore the Broken Cloud Effect in a radiative transfer model has been examined. The used model is called GRIMALDI (Scheirer und Macke (2001)) and is based on the monte carlo method. The clouds used in the model are from the nonhydrostatic cloud model GESIMA and a statistical cloud modell CLABAUTAIR. Additionally the case without a cloud has been simulated to make a look at the enhancements possible. In the model the dependency on the surface albedo could be seen too. So the enhancements with a surface albedo of 0.9 are much bigger than the enhancements with a surface albedo of 0.2. The enhancements in the model are much bigger than the enhancements out of observations. In addition the case has been found that the impact of clouds can differ in several spectralranges. If the radiation in the UV is increased the radiation in the visible or the IR can bedecreased. The same with the others.

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