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Copyright 2008 by the American Geophysical Union. This research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Atlantic Innovation Fund (ACOA), and project CGL2005-06097 of the Spanish MEC. M.B.S. was partially funded by a graduate fellowship from the Atlantic Computing Excellence Network (ACEnet). Part of this work was carried out while J.F.G.R. was a James Chair Professor at STFX. J.F.G.R. was additionally funded by a Ramón y Cajal grant. Special thanks to Lisa Kellman, Asfaw Bekele, Dave Risk, and Nick Nickerson for insightful conversations and to Louise Bodri and Robert Harris for their thoughtful reviews of an earlier version of the manuscript., General circulation models (GCMs) are currently able to provide physically consistent simulations of millennial climate variability in which estimations of external forcing factors are incorporated as boundary conditions. Climate reconstruction attempts to recover as faithfully as possible past climate variability using a variety of independent and climate-sensitive sources of information. By deriving strategies of comparison between GCM simulations and proxy data, or directly recorded data such as subsurface thermal profiles, the agreement between model and observations can be assessed. Thermal profiles obtained from the boreholes of North America were grouped into eight geographically discrete ensembles and averaged to form robust, representative profiles. The gridded output from the three distinct integrations of the GCM ECHO-g were similarly averaged by region. These simulated, millennial, paleoclimatic histories were then forward modeled to arrive at the subsurface thermal profiles that would result from the temperature trends at the surface. These forward modeled profiles were then compared with the borehole average thermal anomaly profile in each region. In most of the regions studied, the externally forced runs from ECHO-g are in better agreement with underground temperature anomalies than with the control run, suggesting that boreholes are sensitive to external forcing. Not only do ECHO-g simulations demonstrate better agreement with borehole data when considering variable external forcing factors, but ECHO-g also appears to broadly describe qualitative aspects of long-term climatic trends at a regional scale., Natural Sciences and Engineering Research Council of Canada (NSERC), Atlantic Innovation Fund (ACOA), Ministerio de Educación y Ciencia (MEC), España, Atlantic Computing Excellence Network (ACEnet), Programa Ramón y Cajal (MEC), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

Copyright 2005 by the American Geophysical Union. We thank the two reviewers and Drs. D. Bray, J. Luterbacher, M. Montoya and E. Xoplaki for their comments and proof reading of this manuscript. This work was partially funded by the DEKLIM Program of the German BMBF, the EU project SO&P and by the project REN-2000-0786Cli of the Spanish CICYT., The spatial patterns of surface air-temperature variations in the period 1000 to 2100, simulated with the ECHO-G atmosphere-ocean coupled model, are analyzed. The model was driven by solar, volcanic and greenhouse gas forcing. The leading mode of temperature variability in the preindustrial period represents an almost global coherent variation of temperatures, with larger amplitudes over the continents and Northern Hemisphere. This mode also describes a large part of the spatial structure of the warming simulated in the 21st century. However, in the 21st century, regional departures from this spatial structure are also present and can be ascribed to atmospheric circulation responses to anthropogenic forcing in the last decades of the 21st century., DEKLIM Program (BMBF), Alemania, Unión Europea (UE), Comisión Interministerial de Ciencia y Tecnología (CICYT), España, Startseite des Webauftritts des Bundesministeriums für Bildung und Forschung (BMBF), Alemania, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

The record-low thermospheric density during the last solar minimum has been reported and it has been mainly explained as the consequence of the anomalously low solar extreme ultraviolet (EUV) irradiance. In this study, we examined the variation of the energy budget to the Earth's upper atmosphere during last solar cycle from both solar EUV irradiance and geomagnetic energy, including Joule heating and particle precipitation. The globally integrated solar EUV power was calculated from the EUV flux model for aeronomic calculations (EUVAC) driven by the MgII index. The annal average of solar power in 2008 was 33 GW lower than that in 1996. The decrease of the globally integrated geomagnetic energy from 1996 to 2008 was close to 29 GW including 13 GW for Joule heating from Weimer (2005b) and 16 GW for particle precipitation from NOAA Polar-Orbiting Environmental Satellites (POES) measurements. Although the estimate of the solar EUV power and geomagnetic energy vary from model to model, the reduction of the geomagnetic energy was comparable to the solar EUV power. The Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) simulations indicate that the solar irradiance and geomagnetic energy variations account for 3/4 and 1/4 of the total neutral density decrease in 2008, respectively.