Reconstruction of Upper-Level Temperature and Geopotential Height Fields for the Northern Extratropics back to 1920 Technical report Thomas Griesser, Stefan Brönnimann, Andrea Grant, Tracy Ewen, Alexander Stickler Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland Institute for Atmospheric and Climate Science ETH Zurich Universitätstr. 16 CH-8092 Zurich Switzerland 8 June 2008