Rickert, Tilman (2010) Eiszeiten in einem einfachen Klimamodell. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 99 pp.

Preview

Text TRickert_Dipl_2010.pdf - Published Version Available under License German copyright act UrhG. Download (21MB)

Abstract

This study reports on further development of the Globally Resolved Energy Balance Model (GREB) [Dommenget, Floeter, 2010 submitted] for paleoanalysis on timescales between millennia and hundred thousands of years. For that purpose, the incoming solar radiation and its underlying Milankovitch theory [Milankovitch, 1941] have been analyzed. Subsequently, various experiments have been carried out, forced by different, fictitious and real insolation patterns. The outcomes have been analyzed by statistical methods in order to judge the model by its capacities and possibilities. The conceptual GREB-Model reduces the Earth’s climate to a hand full of its most important processes, such as incoming shortwave and outgoing long-wave radiation, sea ice, ice albedo and water vapor feedbacks, etc pp. These processes are described by a set of highly reduced bulk formulas and result in an efficient and fast, conceptual model. It don’t feature ice sheet dynamics and has only a fix atmospheric carbon dioxide concentration. The Milankovitch cycles of eccentricity, obliquity and precession are statistically examined based on the insolation patterns calculated as Berger [1978] for the last 3 million years. They has been individually analyzed by EOF- and spectral Analysis, both individually and altogether. Hence, the most variance is explained by precession and eccentricity, the obliquity only explains 2.5% of the variance. Furthermore, the effects of global, zonal and annual averaging on the frequencies of the insolation variations are studied. The experimental part contains model runs with divers insolation forcings varying from simple reductions of the solar constant via chaotic strengths in seasonality to the real time serie of real insolation patterns, calculated as Berger [1978] and Berger and Loutre [1991]. For the last glacial maximum (22 kyr BP, i. e. 22.000 years before present), REB calculates a weak global cooling, that is stronger at the poles. Otherwise there are no more similarities to the calculation of a complex circulation model [Kutzbach et al., 1998]. In comparison to temperature data from a paleo-reconstruction of the past 400 kyr [Petit et al., 1999], the accordingly GREB-simulated curve shows a too high sensitivity, a periodicity of 40 instead of 100 kyr, but nevertheless a quite good correlation of 0.65 at low frequencies (periods above 70 kyr). Further topics are the linkage between seasonality and global mean temperature and the dominance of the summer insolation at 65° N.

Actions (login required)

View Item