Clim. Past Discuss., 9, 3371-3398, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper is under review for the journal Climate of the Past (CP).
Statistical downscaling of a climate simulation of the last glacial cycle: temperature and precipitation over Northern Europe
N. Korhonen1,3, A. Venäläinen1, H. Seppä2, and H. Järvinen3
1Finnish Meteorological Institute, Climate Change Research Unit, Helsinki, Finland
2University of Helsinki, Department of Geosciences and Geography, Helsinki, Finland
3University of Helsinki, Department of Physics, Helsinki, Finland

Abstract. Earth System Models of Intermediate Complexity (EMICs) have proven to be able to simulate the large-scale features of glacial-interglacial climate evolution. For many climatic applications the spatial resolution of the EMICs' output is, however, too coarse, and downscaling methods are needed. We used Generalized Additive Models (GAMs) for downscaling the large-scale output of an EMIC. GAMs are regression models in which a combination of explanatory variables are related to the response through a sum of spline functions. We calibrated the GAMs using observations of the recent past climate and the results of short time-slice simulations of glacial climate performed by the relatively high-resolution general circulation model CCSM and the regional climate model RCA3. As explanatory variables we used the output of a simulation by CLIMBER-2 EMIC of the last glacial cycle, coupled with the SICOPOLIS ice sheet model, i.e., the large-scale temperature and precipitation data of CLIMBER-2, and the elevation, distance to ice sheet, slope direction and slope angle from SICOPOLIS. The fitted GAMs were able to explain more than 96% of the temperature response with a correlation of > 0.98 and more than 59% of the precipitation response with a correlation of >0.72. The first comparison with two pollen-based reconstructions of temperature for Northern Europe showed that CLIMBER-2 data downscaled by GAMs corresponded better with the reconstructions than did the bi-linearly interpolated CLIMBER-2 surface temperature.

Citation: Korhonen, N., Venäläinen, A., Seppä, H., and Järvinen, H.: Statistical downscaling of a climate simulation of the last glacial cycle: temperature and precipitation over Northern Europe, Clim. Past Discuss., 9, 3371-3398, doi:10.5194/cpd-9-3371-2013, 2013.
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