| The present study describes the climatology of extreme events of surface temperature. Using both data analysis and model simulations, we investigated the frequency, duration and structure of extreme events. After developing objective methods to identify "extreme events", we consistently applied them to all data used in this study, focusing mainly on two particular regions: Europe and North America. We utilized 54 years (1950--2003) of Reanalysis data and we compared and contrasted the space-time structure of extreme events during 1950--1976 and 1977--2003. We found that there has been an increase in the warm extremes in Europe and continental Canada and a general decrease of cold spells. Analyzing the spatial-temporal scale of their "structure" we found that an event, either warm or cold, that affects a larger area is expected to last longer, and longer and extended warm events are also more intense. The techniques and methods used for analysis of Reanalysis data were also applied to model simulations with increasing concentration of greenhouse gases to evaluate how the occurrence of extreme warm and cold events might change in the future. Even though the models agree in projecting a significant increase of warm events and decrease of cold events in the 21st century, they give different estimates of extreme events on regional scales.; We identified the Mediterranean SSTA as a common feature for major warm events in the central-western European region. The European heat wave of summer 2003 was then taken as a case study. After a detailed diagnosis of the event, AGCM simulations were performed to investigate the role of ocean and land boundary conditions. In particular we tested the influence of the global SST and local Mediterranean SST in creating and maintaining the heat wave. We successfully simulated the summer 2003 heat wave by using global observed SST. We also found that the local Mediterranean SSTA played an important role in the evolution of the heat wave, explaining more than half of the global SST effect. |
