Bachelor Thesis

Untersuchung des Mikroklimas des EVENT-Experimentes mittels eines horizontal beweglichen Messsystems

Carsten Schaller (05/2012-09/2012)

Support: Jörg Hübner, Thomas Foken

The anthropogenic climate change increases the mean of meteorological parameters like air temperatures. Thus, it increases the probability of occurrence of known extreme events. Simultaneously, the variance rises, so that events at the lower end of the scale continue to be possible. However, the probability of occurrence of new, unknown extremes increases. The consequences for ecosystems resulting from this are unknown. In the experiment EVENT II, the impacts of extreme drought on semi-natural grassland are tested. For that purpose, rain-out shelters are used to keep o the precipitation from the blocks to be examined by a membrane roo ng. However, the installation of this construction leads to changes in size of further meteorological parameters, a fact which is experimentally investigated in this study. A horizontal mobile measuring system, which runs on a railway track 1.20 m above the ground, is applied for that. It crosses the covered areas and the spaces of open land between them. The data acquisition was carried out between May, 29 to June 30, 2012. Due to the in uence of the dynamic error, spatial gradients can only be proved qualitatively without a further data correction. However, stationary thermometers show a gradient of a minimum temperature near the ground of up to 0.8 Km-1. Thus, it can be assumed that the conditions at the edges of the shelter do not necessarily have to correspond to those in the middle of it. The data of the measuring points, gained in the driving direction from the middle of the shelter to the point 1 m before the edge of the shelter, are not signi cantly a ected by the dynamic error. Hence it is no problem to determine the di erences between outdoor spaces and the shelters. Relevant times for measurement were 4 a.m. - 8 a.m., 11 a.m. - 3 p.m. and 6 p.m. - 10 p.m. (CET) at cloudless and clouded skies respectively. The membrane of the shelter reduces global radiation by 22 % approx., the re ected irradiance does not decrease proportional to that. Thus, the albedo under the shelter increases by about 5 - 6 %. Due to a long-wave incoming radiation, which is up to 17 % higher, as well as the long-wave outgoing radiation, which is up to 1.5 % higher, the long-wave net radiation is more equalized. By day, the mean air temperature increases by up to 0.4 K, whereas in the late evenings, it decreases by up to 0.3 K. During the day the relative air humidity is up to 1 % higher, in the late evenings this value is at 1.8 %. The CO2-concentration does not show any relevant changes.

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last modified 2012-09-20