| Autor: |
Laurent Vuilleumier, Julian Gröbner, Christine Aebi, Niklaus Kämpfer |
| Rok vydání: |
2017 |
| Předmět: |
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| DOI: |
10.5194/amt-2017-184 |
| Popis: |
The current study analyses time series of cloud radiative effect during daytime depending on cloud fraction and cloud type at two stations in Switzerland. Information about fractional cloud coverage and cloud type is retrieved from images taken by visible all-sky cameras. The longwave cloud radiative effect (LCE) for low-level clouds and a cloud coverage of 8 octas has a median value between 57 and 71 Wm−2. For mid- and high-level clouds the LCE is significantly lower. It is shown that the fractional cloud coverage, the cloud base height (CBH) and integrated water vapour (IWV) all have an influence on the magnitude of the LCE. These observed dependences have also been modelled with the radiative transfer model MODTRAN5. The relative values of the shortwave cloud radiative effect (SCErel) for low-level clouds and a cloud coverage of 8 octas are between −88 to −61 %. Also here the higher the cloud is, the less negative the SCErel values are. In cases where the measured direct radiation value is below the threshold of 120 Wm−2 the SCErel decreases substantially, while cases where the measured direct radiation value is larger than 120 Wm−2 lead to a SCErel of around 0 %. In 13 % and 8 % of the cases in Davos and Payerne respectively a cloud enhancement has been observed with a maximum in the cloud class cirrocumulus-altocumulus at both stations. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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