Evolução do Clima do Atlântico Norte; o papel dos Bloqueios e ciclones no clima do Sul da Europa Passado, Presente e Futuro (ENAC)

It is now widely accepted that the emission into the atmosphere of large amounts of greenhouse gases of anthropogenic origin is partially responsible for recent climate trends at the global scale (1). However, the capacity to separate the roles of natural and human influences on climate change has only recently been elucidated at the global (or hemispheric) scales for surface air temperature, precipitation or sea level pressure as shown on the recent report of IPCC (2). Climate change at a regional level can be
more difficult to understand than changes occurring at the global or hemispheric scales. Recent trends in temperature and precipitation as well as climate change scenarios under a warmer planet can be amplified or partially offset at the regional scale by changes of atmospheric circulation (2). It is therefore important to understand the role of several large-scale patterns that produce relevant climatic impact on a given region and to provide an assessment of their changes (patterns, trends variability) over the
historical period. General Circulation Models (GCMs) provide a powerful tool to explore the behaviour of the synoptic and large-scale phenomena in the past and future, where no detailed observations exist. Among these large-scale patterns two exert a significant role on the precipitation regime of southern Europe and the Mediterranean basin (3); the North Atlantic Oscillation (NAO) and the Scandinavian Pattern (SCAN). The NAO, the most important large-scale variability mode of the northern hemisphere, modulates considerably the atmospheric flow from the west by shifting the polar jet and the associated preferred paths of storm-tracks (4, 5).
The SCAN pattern has a more regional spatial extent and is usually associated with the occurrence of blocking patterns (with typical durations of 5-20 days) which influence the passage of cyclones and moisture to western Europe, often shifting systems towards the Mediterranean basin (6), or promoting the occurrence of extreme cold (winter) and warm (summer) extremes over Iberia. Persistent strong phases of the SCAN or the NAO have huge impact on storm-tracks and blocking events, and therefore on the climate of southern Europe and Mediterranean, particularly in Iberia (3) and are one of the primary causes of extreme events occurrence over the region (7, 8).

The ultimate goal of this proposal is to evaluate the behaviour of extra-tropical cyclones and blocking events and their linkages with extreme events (i) throughout the last millennium; and (ii) in future climate change scenarios by using climate simulations of several state-of-the-art GCMs. Project ENAC will apply state-of-the-art blocking (9) and storm tracking (10) techniques to the last generation of GCMs available. Among them, millennial simulations of the Max-Planck ECHO-G model and ECMWF-based EC-EARTH model will be used. Besides the standard Reanalyses databases provided by NCEP/NCAR and ECMWF the team will have soon access to the 20th century reanalysis dataset, developed by CIRES/NOAA, and to which the IDL team contributed through a digitalization project funded by FCT (SIGN). Diagnosis will be performed for the entire Northern Hemisphere, but with particular emphasis over the Euro-Atlantic sector. Concerning the past climate, particular attention will be devoted to evaluate these associations during specific anomalous periods such as the Little Ice Age (LIA), or the Medieval Warm period. Regarding extreme events, major emphasis will be placed in long-lasting precipitation (droughts) and temperature (heat waves) extremes over Europe.
The IDL team has acquired a large experience in developing automatic methods to identify and track specific weather systems, or circulation patterns including weather types (11,12), NAO and associated storm-tracks (4, 5, 12); blocking (6, 9), SCAN pattern (3, 13) and extratropical cyclones (10, 14). Moreover, the team has also a large experience to link unusual circulation patterns with extreme events such as heatwaves (7, 15), wet and dry periods (5) or severe droughts (8). Some of these publications correspond to the deliverables obtained in a previous project also funded by FCT (VAST).