Solar signals in tropospheric re-analysis data: Comparing NCEP/NCAR and ERA40

In this paper we present the results of identical analyses of the NCEP/NCAR and ERA40 re-analysis data sets and show that the detected Sun-climate relations are substantially weaker in the ERA40 data than in the NCEP data. We argue that this largely is due to the presence of temporal inhomogeneities in ERA40 having a substantial impact on decadal signals, which strongly affects the observed Sun-climate relations as well as climate trends. The nature of the NCEP-ERA40 differences, their influence on the detection of Sun-climate relations, and their possible causes are discussed.