Chapter 6 ENSO Forcing of Climate Variability over the North Atlantic/European Region in a Warmer Climate Conditions

摘要

Changes in winter climate variability in the North Atlantic European (NAE) region associated with El Nino-Southern Oscillation (ENSO) forcing in a warmer climate are investigated. The study is based on two 20-member ensembles of numerical integrations by utilizing an atmospheric general circulation model (AGCM) of intermediate complexity. Current climate experiment is based on simulations forced with observed sea-surface temperatures (SST) for the period 1855-2002. The warmer climate corresponds to the doubled CO, concentration with SST forcing represented by the same SST anomalies as in the current climate experiment superimposed on the climatological SST that was obtained from a complex atmosphere-ocean general circulation model forced with the doubled CO_2. A composite analysis of atmospheric response is based on categorization into warm and cold composites according to the strength of SST anomalies in the Nino3.4 region. In the current climate, ENSO impact on the winter interannual variability in the NAE region is rather weak, but is still discernible and statistically significant. Over the south-western part of Europe warm (cold) ENSO events are mainly associated with warmer (colder) and dryer (wetter) conditions than usual. According to the results of numerical simulations in the climate with doubled CO, concentrations, substantial modifications of ENSO influence on the NAE region are found. The spatial pattern of the ENSO impact on the NAE precipitation projects onto the distribution of differences between the warmer climate and the current climate precipitation climatology fields. Therefore, a considerable ENSO impact on temperature and precipitation may be expected in warmer climate conditions implying a possibility of greater importance of tropical-extratropical teleconnections for future climate variability in the NAE region. Since temperature and precipitation are the variables of great interest of policy makers for adaptation and mitigation purposes, their proper representation is essential for climate projections.