HR: 08:30h
AN: PP51A-03    [PDF]
TI: Centennial scale climate variations and their spatial dimensions in coupled GCM simulations of the last millennium
AU: * Ammann, C M
EM: ammann@ucar.edu
AF: Climate and Global Dynamics Division, National Center for Atmospheric Research 1850 Table Mesa Drive, Boulder, CO 80307-3000 United States
AU: Joos, F
EM: joos@climate.unibe.ch
AF: Institute of Climate and Environmental Physics, University of Bern Sidlerstrasse 9, Bern, BE 3012 Switzerland
AU: Tomas, R A
EM: tomas@ucar.edu
AF: Climate and Global Dynamics Division, National Center for Atmospheric Research 1850 Table Mesa Drive, Boulder, CO 80307-3000 United States
AB: Multi-decadal and century scale climate variations have been proposed to occur either purely internal to the climate system or in response to external perturbations. The separation between these different sources is not only important for our understanding of past climates but it also bears significant implications for what we have to expect from the future. External forcing, such as solar irradiance variations and explosive volcanism, has recently been found to behave surprisingly linear both in terms of response to individual forcings as well as in combination of each other. But it is unclear if this also holds back in time. In particular, when including the most significant natural climate variations during the last millennium, namely the episodes of the Little Ice Age, it remains to be demonstrated that no low-frequency variation from inside of the climate system could be the main driver. In fact, such an internal cause has been proposed using global ocean circulation changes as the primary mechanism. In order to identify contributions to climatic variations resulting from both external and internal sources, both temporal and spatial scales might hold valuable information. It is crucial in this context to study the system in a framework that allows all climate components to interact and respond. Here, we use the fully coupled NCAR Paleo-CSM to present climate variation on centennial time scales as simulated in fully forced experiments of the last millennium. We compare both temporal and spatial patterns to fingerprints that would be expected from internal modes as well as from external forcing. The question is addressed if internally caused fluctuations can be systematically separated from external influences through characteristic imprints on global or hemispheric climate, and to what degree models that can be run for 1000 years can be useful, selectively, even on the regional scale.
DE: 0370 Volcanic effects (8409)
DE: 1600 GLOBAL CHANGE (New category)
DE: 3337 Numerical modeling and data assimilation
DE: 3344 Paleoclimatology
DE: 7536 Solar activity cycle (2162)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting