Assimilation of Instrumental Observations, Historical Climate Indices and Tree-Ring Data into an Atmospheric General Circulation Model in the Period 1600 to 2000
One of the backbones of numerical weather prediction is the assimilation of all available observations into models to achieve initial conditions close to reality. The assimilation idea also revolutionized climate research with reanalysis becoming the most important dataset for the last century. Recently, paleo-climatologist began developing new methodologies with the intention to assimilate sparse and temporally averaged proxy information instead of satellite data and instrumental observations. EKF400 is the first monthly resolved paleo-reanalysis covering the period 1603 to 2003. Early instrumental temperature and surface pressure observations, temperature indices derived from historical documents and temperature and moisture sensitive tree-ring proxies were assimilated into an ensemble of atmospheric general circulation model using a Kalman-filtering technique. The resulting paleo-reanalysis combines the advantage of traditional reconstruction methods of being as close a possible to observations with the advantage of climate models of being physically consistent and having 3-dimensional information about the state of the atmosphere through time and for various variables.
We would like to thank the CSCS for their support in conducting the ECHAM simulations. The project was supported by the Swiss National Science Foundation Project REUSE and Stefan Brönnimann additionally by the EC FP7 project ERA-CLIM2.