HR: 13:40h
AN: GC43B-01 INVITED    [Abstracts]
TI: Data assimilation over the last millennium using a large ensemble of simulations
AU: * Goosse, H
EM: hgs@astr.ucl.ac.be
AF: Institut d'Astronomie et de Geophysique, Universite catholique de Louvain 2 Chemin du Cyclotron, Louvain-la-Neuve, 1348, Belgium
AU: Mann, M E
EM: mann@psu.edu
AF: Department of Meteorology and Earth and Environmental Systems Institute, Pennsylvania State University Department of Meteorology 503 Walker Building, University Park, PA 16802-5013, United States
AU: Renssen, H
EM: hans.renssen@geo.falw.vu.nl
AF: Faculty of Earth and Life Sciences, Vrije Universiteit , De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands
AU: Timmermann, A
EM: axel@hawaii.edu
AF: IPRC, SOEST, University of Hawaii Pacific Ocean Science and Technology Bldg., Room 401, 1680 East-West Road, Honolulu, 96822, United States
AB: A simulation is performed over the past millennium using a three-dimensional climate model of intermediate complexity that is forced to follow temperature histories obtained from a recent compilation of well-calibrated surface temperature proxies. This is achieved using a simple data assimilation technique that could be briefly described as follows. For each year, a large ensemble of simulation is performed (96 here). The member of the ensemble that is the closest to observations is then selected as representative for this particular year and used as the initial condition for the subsequent year. The distance between the model results and the proxy record is measured by a cost function using reconstructed and simulated temperatures at the locations where the proxies are available. The best simulation retained is the one that minimizes this cost function. The simulation obtained by this technique provides a continuous record over the past millennium that is compatible with model physics, with the forcing applied and with the available proxy-records. In a first step, the simulated temperatures over the last 150 years are compared to estimates obtained using only information from thermometers in order to demonstrate the validity of the techniques as well as to provide estimates of the errors bars on this new reconstruction. In a second step, the simulated temperatures over the whole millennium are compared at quasi- hemispheric-scales with the reconstructions based on statistical techniques. The simulated pattern of anomalies are then analyzed as well as the mechanisms responsible for the regional changes, with a particular focus over Europe and North America. The results are then compared to the ones of other data assimilation techniques used to study the climate of the last millennium.
UR: http://www.astr.ucl.ac.be/index.php?page=Wokshop_assim
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1622 Earth system modeling (1225)
DE: 3315 Data assimilation
DE: 3344 Paleoclimatology (0473, 4900)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting