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In this work we performed an analysis on the impacts of blocking episodes on seasonal and annual European precipitation and the associated physical mechanisms. Distinct domains were considered in detail taking into account different blocking center positions spanning between the Atlantic and western Russia. Significant positive precipitation anomalies are found for southernmost areas while generalized negative anomalies (up to 75 % in some areas) occur in large areas of central and northern Europe. This dipole of anomalies is reversed when compared to that observed during episodes of strong zonal flow conditions. We illustrate that the location of the maximum precipitation anomalies follows quite well the longitudinal positioning of the blocking centers and discuss regional and seasonal differences in the precipitation responses. To better understand the precipitation anomalies, we explore the blocking influence on cyclonic activity. The results indicate a split of the storm-tracks north and south of blocking systems, leading to an almost complete reduction of cyclonic centers in northern and central Europe and increases in southern areas, where cyclone frequency doubles during blocking episodes. However, the underlying processes conductive to the precipitation anomalies are distinct between northern and southern European regions, with a significant role of atmospheric instability in southern Europe, and moisture availability as the major driver at higher latitudes. This distinctive underlying process is coherent with the characteristic patterns of latent heat release from the ocean associated with blocked and strong zonal flow patterns. We also analyzed changes in the full range of the precipitation distribution of several regional sectors during blocked and zonal days. Results show that precipitation reductions in the areas under direct blocking influence are driven by a substantial drop in the frequency of moderate rainfall classes. Contrarily, southwards of blocking systems, frequency increases in moderate to extreme rainfall classes largely determine the precipitation anomaly in the accumulated totals. In this context, we show the close relationship between the more intrinsic torrential nature of Mediterranean precipitation regimes and the role of blocking systems in increasing the probability of extreme events. [ABSTRACT FROM AUTHOR]

The present work aims at evaluating the impacts of a climate change scenario on the hydrography and dynamics of the Iberian Upwelling System. Using regional ocean model configurations, the study domain is forced with three different sets of surface fields: a climatological dataset to provide the control run; a dataset obtained from averaging several global climate models (GCM) that integrate the Intergovernmental Panel for Climate Change (IPCC) models used in climate scenarios, for the same period as the climatological dataset; and this same dataset but for a future period, retrieved from the IPCC A2 climate scenario. After ascertaining that the ocean run forced with the GCM dataset for the present compared reasonably well with the climatologically forced run, the results for the future run (relative to the respective present run) show a general temperature increase (from +0.5 to +3 °C) and salinity decrease (from −0.1 to −0.3), particularly in the upper 100-200 m, although these differences depend strongly on season and distance to the coast. There is also strengthening of the SST cross-shore gradient associated to upwelling, which causes narrowing and shallowing of the upwelling jet. This effect is contrary to the meridional wind stress intensification that is also observed, which would tend to strengthen the upwelling jet. [ABSTRACT FROM AUTHOR]

In this work we reassess the impacts of blocking patterns on precipitation regimes in the Iberian Peninsula, distinguishing between north Atlantic and European blocking. For this we take full advantage of the recently developed high-resolution datasets for the Iberian countries. Precipitation anomalies during blocking events obtained with this dataset allow a much finer regional characterization of the impacts in both average and extreme daily precipitation, particularly when compared to widely used low-resolution reanalysis datasets. Blocked patterns induce a negative-positive dipole of precipitation anomalies from northwest to southeast Iberia. Increases are widespread during Atlantic blocks and pronounced in southern and eastern areas of Iberia, while during European blocks they are more spatially restricted, with increases above 50 % in coastal Mediterranean areas, which represents a considerable fraction of the annual precipitation. Blocking impacts in precipitation are nearly opposite to those found during strong zonal flow situations, but there are also some asymmetries in the precipitation responses. A significant increase in cyclones and cut-off lows frequency southwards of blocking structures is related to precipitation excesses over southern and eastern areas, where dynamical factors and local processes play a crucial role. On the contrary, precipitation deficits in northwest Iberia during blocking episodes are better explained by a reduction in north Atlantic frontal activity and simultaneous decreases in large-scale moisture advection towards northern Iberia. We show that these anomalies during blocking result from changes in precipitation amount rather than from increases in rainy days, pointing to more extreme rainfall regimes, particularly in southeastern Iberia. Finally, an Extreme Value Analysis was performed, fitting Generalized Pareto Distributions to precipitation extremes. Results show that the different extreme precipitation regimes of northwest and Mediterranean regions are partially determined by opposite anomalies of the zonal flow. Thus, heavy precipitation events in Mediterranean areas are usually short-lived and frequently associated with blocking conditions, while in northwest Iberia the total accumulations during rainfall episodes are more important for triggering extreme events and they are mainly related to strong westerly flows. [ABSTRACT FROM AUTHOR]