Diploma Thesis

Behandlung der Energiebilanzgleichung in drei verschiedenen SVAT-Modellen

Daniela Kracher (10/2005-05/2006)

Support: Thomas Foken

Usually current measuring methods are only enabled to close the energy balance on the earth’s surface by using a residual. Models demand an entirely closed energy balance, which is done in different ways. This thesis examines the effect of the residual on the results of models and in how far that depends on the methods utilized for closing the energy balance in the models, the optimization of the parameters and the equations used. Therefore the 1D versions REMO, SEWAB and TERRA, which were provided from the GKSS institute in Geesthacht, are examined and compared with measured data from the LITFASS-2003 experiment, which was conducted during May and June 2003 in the experimental fields of the Meteorological Observatory Lindenberg (MOL). The Parameters optimized for the turbulent fluxes yield better results, but are often not consistent with local characteristics and differ between the models. Consequently the models are performed with optimized and a set of selected parameters, which correspond to the respective sites. SEWAB closes the energy balance by using an iteration of the surface temperature, through which the influence of the residual is divided up to all fluxes. Concerning REMO and TERRA, the closing is done by balancing the soil heat flux from the other components of the energy balance equation. The result is an extreme overestimation of this heat flux. The optimization of the parameters has an impact on the splitting of the energy available and its distribution to the turbulent heat fluxes. It does not influence the effect of the residual on the results. Due to the current state of knowledge the energy balance at the surface can not be closed because of the underestimation of the turbulent fluxes. Therefore, the method SEWAB uses gives better results than the one used in REMO and TERRA. SEWAB’s parameters regarding the characteristics of the soil work out more properly because of the specific calculation of the soil heat flux. REMO and TERRA do not demand such complex parameterization of the soil. This is one of several reasons which might lead to an apparent time loss in the results. The procedures of closing the energy balance are more decisive for the results than the parameterization. For this reason it is not possible to attribute the differences in the calculated heat fluxes to differences in the equations and parameters. The simulation with optimized parameters leads to better results; however this fact is not depending on specific modifications of the parameters either.

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last modified 2006-10-16