Renkosik, Niko (2010) Energiebilanz arktischer Bewölkung aus Modell und Beobachtung. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 105 pp.

Preview

Text NRenkosik_Dipl_2010.pdf - Published Version Available under License German copyright act UrhG. Download (7MB)

Abstract

This diploma thesis discusses the effect of clouds under arctic conditions on the energy balance at ground and the impact on sea ice and snow conditions. To calculate the energy balance is used an one-dimensional sea ice model from Andreas Lehmann. He is a scientist at the IFM-GEOMAR in the field of research „theory and modelling “. The model for this thesis is taken from the threedimensional and dynamic ice model BSIOM(Jacob et al. (2006)). The energy balance is made up of incoming solar radiation with the surface albedo, the outgoing and incoming longwave radiation and the latent and sensible heat flux. The radiation flux dominate the energy balance in the Arctic. Therefore at first several parameterizations for incoming shortwave radiation and longwave counter-radiation are analysed with data from the expedition ARK-XXIV/3 of the research vessel Polarstern. For the analysis are put parameterizations for the global radiation from Zillman (1972), Shine (1984), Bennett (1982) and Shine/Bennett. Parameterizations by Maykut und Church (1973), Zillman (1972), König-Langlo und Augstein (1994), Konzelmann et al. (1994) and Zapadka et al. (2007) are used for the study of the longwave counter-radiation. The parameterizations of shortwave radiation can reflect the rough diurnal variations in global radiation. Nevertheless, there are considerable differences between observation and parameterization, if direct sunlight arrives ground under a high degree of cloud cover and it comes to short-term increase in radiation. These increases can not be reproduced by any of the parameterizations. In principle, the parameterizations tend to overestimate low values of shortwave radiation and to underestimate high values. The parameterizations of longwave counter-radiation have significant problems to reflect the diurnal variation of the measured values on some days. Especially after sunrise and before sunset are often the coverages of clouds from the cloud detection algorithms be misinterpreted on the sky imager photos. In these cases the differences between the values of parameterization and observation can be more than 100 W/m2. The analyses of the calculated energy balances with the one-dimensional sea ice model for three locations in the Arctic in the years 2006 to 2009 shows that clouds have a major influence on the radiation balance. Therefore several sensitivity studies are carried out. The sea ice and snow change under different cloud conditions, thus the surface albedo varies. Clouds effect a weakening of shortwave radiation in the Arctic summer. However they provide an all-season increase in longwave counter-radiation. The longwave radiation dominates the energy balance at ground in the Arctic, which is reflected in the model results of the ice thickness. The sea ice is thicker at the end of the year in case of an all-season cloudless sky as a continuous covered sky.

Actions (login required)

View Item